Computational Quantum Chemistry

Analytic potentials are built for all four 2S+1Πu/g states of Li2 dissociating to Li(2S) + Li(3P): 3b(33Πu), 3B(31Πu), 3C(31Πg), and 3d(33Πg). These potentials include the effect of spin-orbit coupling for large internuclear distances, and include state of the art long-range constants. This is the first successful demonstration of fully analytic diatomic potentials that capture features that are usually considered too difficult to capture without a point-wise potential, such as multiple minima, and shelves. Vibrational energies for each potential are presented for the isotopologues 6,6Li2, 6,7Li2, 7,7Li2, and the elusive `halo nucleonic molecule' 11,11Li2. These energies are claimed to be accurate enough for new high-precision experimental setups such as the one presented in {[}Sebastian \emph{et al.} Phys. Rev. A, \textbf{90}, 033417 (2014){]} to measure and assign energy levels of these electronic states, all of which have not yet been explored in the long-range region. Measuring energies in the long-range region of these electronic states may be significant for studying the ab initio vs experiment discrepancy discussed in [Tang et al. Phys. Rev. A, 84, 052502 (2014)] for the C3 long-range constant of Lithium, which has significance for improving the SI definition of the second.

A superluminal quantum-vortex model of the electron and the positron is produced from a superluminal double-helix model of the photon during electron-positron pair production. The two oppositely-charged (with Q = ±e sqrt (2/α) = 16.6e) open-helix spin-½ half-photons compose the double-helix photon. These half-photons separate and curl up their separated superluminal single-helical trajectories to form an electrically-charged superluminal closed-helix spin-½ quantum-vortex electron model and a corresponding positron model. The helical radius and the Dirac equation's zitterbewegung angular frequency of the quantum vortex electron and positron models equal the helical radius and zitterbewegung angular frequency of the two spin-½ half-photons, each of energy E = mc^2 , that composed the double-helix photon model of energy E = 2mc^2 from which the electron and positron models were produced. The photon and electron models are also compatible when a photon of energy E > 2mc^2 produces a relativistic electron-positron pair. Implications of the quantum vortex electron model for electron stability are discussed.

We report re-optimization of a recently proposed long-range corrected (LC) hybrid density functional [J.-D. Chai and M. Head-Gordon, J. Chem. Phys., 2008, 128, 084106] to include empirical atom-atom dispersion corrections. The resulting functional, oB97X-D yields satisfactory accuracy for thermochemistry, kinetics, and non-covalent interactions. Tests show that for non-covalent systems, oB97X-D shows slight improvement over other empirical dispersion-corrected density functionals, while for covalent systems and kinetics it performs noticeably better. Relative to our previous functionals, such as oB97X, the new functional is significantly superior for non-bonded interactions, and very similar in performance for bonded interactions.

For a long time, one of my dreams was to describe the nature of uncertainty axiomatically, and it looks like I've finally done it in my co∼eventum mechanics! Now it remains for me to explain to everyone the co∼eventum mechanics in the most approachable way. This is what I'm trying to do in this work. The co∼eventum mechanics is another name for the co∼event theory, i.e., for the theory of experience and chance which I axiomatized in 2016 [1, 2]. In my opinion, this name best reflects the co∼event-based idea of the new dual theory of uncertainty, which combines the probability theory as a theory of chance, with its dual half, the believability theory as a theory of experience. In addition, I like this new name indicates a direct connection between the co∼event theory and quantum mechanics, which is intended for the physical explanation and description of the conict between quantum observers and quantum observations [4]. Since my theory of uncertainty satises the Kolmogorov axioms of probability theory, to explain this co∼eventum mechanics I will use a way analogous to the already tested one, which explains the theory of probability as a theory of chance describing the results of a random experiment. The simplest example of a random experiment in probability theory is the " tossing a coin ". Therefore, I decided to use this the simplest random experiment itself, as well as the two its analogies: the " "flipping a coin " and the " spinning a coin " to explain the co∼eventum mechanics, which describes the results of a combined experienced random experiment. I would like to resort to the usual for the probability theory " coin-based " analogy to explain (and first of all for myself) the logic of the co∼eventum mechanics as a logic of experience and chance. Of course, this analogy one may seem strange if not crazy. But I did not come up with a better way of tying the explanations of the logic of the co∼eventum mechanics to the coin-based explanations that are commonly used in probability theory to explain at least for myself the logic of the chance through a simple visual " coin-based " model that clarifies what occurs as a result of a combined experienced random experiment in which the experience of observer faces the chance of observation. I hope this analogy can be useful not only for me in understanding the co∼eventum mechanics.

In the present account the nature of aromaticity/antiaromaticity of fourteen metallic complexes/clusters are reexamined. These species were classified as aromatic by means of different nucleus independent chemical shift- (NICS) based approaches, previously. Visualization of the current density and magnetizability of atomic basins reveals that none of the studied systems are magnetic aromatic, i.e. sustain diamagnetic ring current. It is demonstrated that negative NICS values near the ring plane of the studied molecules originates from remarkably strong local paramagnetic current around their transition metal atom nuclei. This phenomenon has been observed only for Sc3– all-metal cluster but current study demonstrates that the influence of the local paramagnetic currents around transition metal atoms on NICS is a general phenomenon that must be carefully considered prior to classification of the metallic systems as aromatic. Furthermore, this study suggests that NICS is not a reliable aromaticity index for transition-metal clusters/molecules.

In the present account we investigate a theoretical link between bond length, electron sharing, and bond energy within the context of quantum chemical topology theories. The aromatic stabilization energy, ASE, was estimated from this theoretical link without using isodesmic reactions for the first time. The ASE values obtained from our method show a meaningful correlation with the number of electrons contributing in the aromaticity. This theoretical link demonstrates that structural, electronic, and energetic criteria of aromaticity –ground-state aromaticity– belong to the same class and guarantees that they assess the same property as aromaticity. Theory suggests that interatomic exchange-correlation potential, obtained from the theory of Interacting Quantum Atoms (IQA), is linearly connected to the delocalization index of Quantum Theory of Atoms in Molecules (QTAIM) and bond length through a first order approximation. Our study shows that the relationship between energy-structure-electron sharing marginally deviates from the ideal linear form expected from the first order approximation. The observed deviation from linearity was attributed to a different contribution of exchange-correlation into the bond energy for the σ- and π-frameworks. Finally, we proposed two-dimensional energy-structure-based aromaticity indices in analogy to the electron sharing indices of aromaticity.

The electronic spectrum of alizarin (AZ) in methanol solution was measured and used as reference data for color prediction. The visible part of the spectrum was modelled by different DFT functionals within the TD-DFT framework. The results of a broad range of functionals applied for theoretical spectrum prediction were compared against experimental data by a direct color comparison. The tristimulus model of color expressed in terms of CIE XYZ and CIE Lab parameters was applied both to experimental and predicted spectra. It was found that the HSE03 method along with the 6-31G(d,p) basis set provides the most accurate color prediction, much better than other commonly used functionals such as B3LYP, CAM-B3LYP or PBE0. Besides, the influence of potential errors, introduced by theoretical predictions on color estimation, was examined for different wavelengths. The obtained results showed that color prediction is significantly dependent on the type of basis set and functional applied. The proposed methodology provides a simple, straightforward and more reliable way of theoretical protocols validation than just a comparison of experimental and estimated values of maximum absorbance wavelength.

Abstract
A completely non-statistical non-linear non-unitary framework in which “God does not play dice …” (Einstein) that describes the physical foundations of consciousness is presented for the first time. At
its core is the insight that the missing link between current physical descriptions of reality and a credible physical framework for consciousness is provided by post-quantum mechanics (PQM): the
extension of statistical linear unitary quantum mechanics for closed systems to a locally-retrocausali non-statistical non-linear non-unitary theory for open systems through the introduction of a backreaction
potential and its implications. PQM is to orthodox QM as General Relativity (GR) is to Special Relativity (SR). PQM and GR both share the same metaphysical organizing principle that one-way actions without a compensating reaction or back-reaction means an incompleteness in the
theoretical model leaving out important physical phenomena. We gleaned the final piece in the puzzle of how consciousness arises from the material world from a result relating to long range collective excitations in microtubules described by Stuart Hameroff in a recent Fetzer Foundation conference in London. Herbert Frohlich suggested that almost any many-particle system when properly pumped far off thermodynamic equilibrium can be put into a robust macro-quantum coherent state immune from
environmental decoherence. Indeed, we suggest that all life forms are an example of Frohlich coherence that is intimately connected with locally-retrocausal PQM back-reaction’s violation of the de Broglie guidance equation that was assumed by Bohm in his 1952 pilot wave theory. Using nature as a guide combined with nano-technology points the way to the construction of naturally conscious artificial intelligence machines capable of hacking into current-day quantum cryptographic networks.
Furthermore, one can imagine attaining the transhumanist agenda. For example, the consciousness of a genius like Stephen Hawking could be uploaded to the post-quantum Cloud and then downloaded to
a healthy body or android.

Quantum chemical calculations using density functional theory and correlated ab initio methods of the 10 p-electron systems (N 6 H 6) 2 + and C 2 N 4 H 6 show that the planar forms are no minima on the potential energy surfaces. The twisted ring structures of the two species are energy minima, but acyclic isomers are much lower in energy. The planar geometries sustain strong diamagnetic ring current comparable with that of benzene. In contrast, the calculated multicenter normalized Giambiagi electron delocalization index I NG suggests that p-delocalization in planar (N 6 H 6) 2 + and C 2 N 4 H 6 is much weaker than in benzene. Since aromaticity is synonymous for a particular stability of cyclic delocalized systems, it may be stated that calculation or measurement of magnetic chemical shifts due to induced ring currents is not a reliable method to ascertain the aromatic character of a molecule. Aromatic compounds exhibit ring current induced magnetic shielding, but the reverse conclusion that ring current induced magnetic shielding identifies aroma-ticity is not justified. Furthermore, the 4n + 2 rule as indicator of aromatic stabilization should only be used in conjunction with the ring size; the nature of the occupied p orbitals must always be examined.

CORRECTED 2ND DRAFT
The no-signaling arguments for orthodox quantum theory assume a violation of the general action-reaction principle that Einstein used to get from special relativity to general relativity. Special relativity had action of spacetime geometry on the geodesic motion of particles without any direct reaction of those particles back on the spacetime geometry. Similarly, Bohm and Hiley pointed out that the no-signaling property of orthodox quantum theory’s entanglement depended on the Schrodinger quantum information pilot field having “no sources.” The pilot field changed the classical world lines of particles without any direct reaction of those particles back on their quantum information pilot field. Such direct back-reaction would result in stand-alone entanglement signals. These entanglement signals seem to violate special relativity because they appear to be spacelike faster-than-the speed of light. However, R. I. Sutherland, building on the 1950’s work of O. Costa de Beauregard, I.J. Good and Fred Hoyle leading back to Wheeler and Feynman (1940 – 47) has shown that the violation of Bell’s inequality is best understood as local retrocausality that is completely relativistically invariant. John Bell knew about this, but rejected it because it seemed to him to contradict free will.  Yakir Aharonov and his students as well as John Cramer and Hoyle and Narlikar have developed these ideas further since the 1950s up to the present time. Of particular experimental interest is Aephraim Steinberg’s work on photon Bohmian trajectories in space using Aharonov’s post-selected “destiny” and pre-selected “history” “weak measurement” technique. The bottom line here is that real Bohmian particle trajectories can be observed – the variables are no longer “hidden” via Aharonov’s weak measurements. This is the most parsimonious understanding of the facts minimizing the algorithmic complexity in the space of possible interpretations of orthodox quantum theory.

Rod Sutherland has shown that the lack of direct back reaction from particle to wave enforcing the no-signaling property of entanglement is precisely the old de Broglie guidance constraint that Antony Valentini characterizes as “sub-quantal equilibrium” with “signal locality” as a limiting case of a more general post-quantum theory. Hagen Kleinert  has also shown that this limiting case is a WKB approximation. Violation of the de Broglie guidance constraint leads to entanglement signaling that may be equivalent to the super-computation around closed timelike curves discussed by Seth Lloyd and others.  These results also apply to the Dirac fermion and the boson gauge theories in Bohmian form.

The application of post-quantum theory’s violation of the de-Broglie guidance constraint corresponding to Antony Valentini’s “sub-quantum non-equilibrium” “signal nonlocality” to naturally conscious AI machines will also be considered.

This paper breaks new ground. It is first a commentary on the following paper by Rod Sutherland. However, second, I will also consider the extension of quantum theory to the more general post-quantum theory that is not considered except in passing in his paper below.  Post-quantum theory obeying Einstein’s general action-reaction principle corresponds to Antony Valentini’s “sub-quantum non-equilibrium” with entanglement signal nonlocality. That is, we do not need a classical signal key to locally decode a message at Bob’s receiver sub-system encoded in the distant sender Alice’s part of the entangled whole system. The message would be in non-equilibrium non-random statistics of the reduced density matrix of Bob’s receiver controlled by Alice even if Alice is inside Bob’s Lorentz invariant future light cone.

Developing a comprehensive method to compute bond orders is a problem that has eluded chemists since Lewis's pioneering work on chemical bonding a century ago. Here, a computationally efficient method solving this problem is introduced and demonstrated for diverse materials including elements from each chemical group and period. The method is applied to non-magnetic, collinear magnetic, and non-collinear magnetic materials with localized or delocalized bonding electrons. Examples studied include the stretched O 2 molecule, 26 diatomic molecules, 3d and 5d transition metal solids, periodic materials with 1 to 8748 atoms per unit cell, a biomolecule, a hypercoordinate molecule, an electron deficient molecule, hydrogen bound systems, transition states, Lewis acid–base complexes, aromatic compounds, magnetic systems, ionic materials, dispersion bound systems, nanostructures, and other materials. From near-zero to high-order bonds were studied. Both the bond orders and the sum of bond orders for each atom are accurate across various bonding types: metallic, covalent, polar-covalent, ionic, aromatic, dative, hypercoordinate, electron deficient multi-centered, agostic, and hydrogen bonding. The method yields similar results for correlated wavefunction and density functional theory inputs and for different S Z values of a spin multiplet. The method requires only the electron and spin magnetization density distributions as input and has a computational cost scaling linearly with increasing number of atoms in the unit cell. No prior approach is as general. The method does not apply to electrides, highly time-dependent states, some extremely high-energy excited states, and nuclear reactions.

Bond order quantifies the number of electrons dressed-exchanged between two atoms in a material and is important for understanding many chemical properties. Diatomic molecules are the smallest molecules possessing chemical bonds and play key roles in atmospheric chemistry, biochemistry, lab chemistry, and chemical manufacturing. Here we quantum-mechanically calculate bond orders for 288 diatomic molecules and ions. For homodiatomics, we show bond orders correlate to bond energies for elements within the same chemical group. We quantify and discuss how semicore electrons weaken bond orders for elements having diffuse semicore electrons. Lots of chemistry is effected by this. We introduce a first-principles method to represent orbital-independent bond order as a sum of orbital-dependent bond order components. This bond order component analysis (BOCA) applies to any spin-orbitals that are unitary transformations of the natural spin-orbitals, with or without periodic boundary conditions, and to non-magnetic and (collinear or non-collinear) magnetic materials. We use this BOCA to study all period 2 homodiatomics plus Mo 2 , Cr 2 , ClO, ClO À , and Mo 2 (acetate) 4. Using Manz's bond order equation with DDEC6 partitioning, the Mo-Mo bond order was 4.12 in Mo 2 and 1.46 in Mo 2 (acetate) 4 with a sum of bond orders for each Mo atom of $4. Our study informs both chemistry research and education. As a learning aid, we introduce an analogy between bond orders in materials and message transmission in computer networks. We also introduce the first working quantitative heuristic model for all period 2 homodiatomic bond orders. This heuristic model incorporates s-p mixing to give heuristic bond orders of 3 4 (Be 2), 1 3 4 (B 2), 2 3 4 (C 2), and whole number bond orders for the remaining period 2 homodiatomics.

In this study, an investigation was performed to understand the interaction between phosphine and (H2O)n clusters (n =1–6). The general interactions involving PH3 and H2O molecules include P-HO and P-OH with bond distances of 2.412–3.065 and 3.174–3.471 Å, respectively. A redshift of the vibrational modes corresponding to the phosphine-degenerated deformation and the symmetric deformation was observed. In addition, a blueshift of the vibrational modes corresponding to symmetric and asymmetric P–H stretching was predicted. A decrease in the dipole moments for the P–H bond contribution was also predicted. In addition, an increase in the phosphorous atom polarizability as well as a slight decrease in the phosphorous p population and an increase in the s population of the P–H bond were estimated. Based on analysis of the atomic charge distribution, the atomic charge distributions were dependent on the population analysis employed, and only some methods were able to characterize the correct behavior of these systems, while most of the population analysis failed to determine the phosphorous charge. The relative stability of the isomers and their dissociation energies were also predicted using Coupled Cluster and Møller–Plesset correlation energy correction. The efficiency of different Density Functional Theory (DFT) methods was evaluated using three basis sets [i.e., 6-311++G(2df, 2pd), 6-311++G(3df, 3pd) and aug-cc-pVTZ]. In these analyses, several functionals, including the generalized gradient approximation (GGA), hybrid-GGA, meta-hybrid-GGA, meta-GGA, double-hybrid-GGA, and functionals such as the empirical London dispersion correction were employed. Most of the functionals exhibited good performance, however the O3LYP, B97-2 and BHandH functionals exhibited the poorest performances.

In contrast to the original Kohn-Sham (KS) formalism, we propose a density functional theory (DFT) with fractional orbital occupations for the study of ground states of many-electron systems, wherein strong static correlation is shown to be described. Even at the simplest level represented by the local density approximation (LDA), our resulting DFT-LDA is shown to improve upon KS-LDA for multi-reference systems, such as dissociation of H 2 and N 2 , and twisted ethylene, while performing similar to KS-LDA for single-reference systems, such as reaction energies and equilibrium geometries. Because of its computational efficiency (similar to KS-LDA), this DFT-LDA is applied to the study of the singlet-triplet energy gaps (ST gaps) of acenes, which are "challenging problems" for conventional electronic structure methods due to the presence of strong static correlation effects. Our calculated ST gaps are in good agreement with the existing experimental and high-level ab initio data. The ST gaps are shown to decrease monotonically with the increase of chain length, and become vanishingly small (within 0.1 kcal/mol) in the limit of an infinitely large polyacene. In addition, based on our calculated active orbital occupation numbers, the ground states for large acenes are shown to be polyradical singlets.

The chemical mechanism of the 1PN formation was successfully studied by using the CCSD(T)/6-311++G(3df,3pd) level of theory. The 1NH3 + 3PH and 4P + NH3 reaction paths are not energetically favorable to form the 1PN molecule. However, the 3NH + 3PH, 4N + 3PH3, 4N + 3PH, 4P + 3NH, and 4P + 2NH2 reaction paths to form the 1PN molecule are only energetically favorable by taking place through specific
transition states to form the 1PN molecule. The NH3 + 3PH, 4N + 1PH3, NH3 + 4P, and 4N + 2PH2 reactions are spin-forbidden and the probability of hopping for these reactions was estimated to be 0 by the Landau–Zener theory. This is the first detailed study on the chemical mechanism for the 1PN formation

Quantum chemical calculations using the density functional theory (DFT) have been applied to the five kinds of polydentate Schiff base compounds (PSCs), act as inhibitors for iron in aerated 2.0 M HNO3 and 2.0 M NaOH media. The structural parameters, such as the frontier molecular orbital energy HOMO (highest occupied molecular orbital), LUMO (lowest unoccupied molecular orbital), energy gap ΔE (ELUMO - EHOMO), the charge distribution, the absolute electronegativity (χ), the fraction of electrons transfer (ΔN) from inhibitors to iron, the dipole moment (μ), the global hardness (η) and the total energy (Etotal) were also calculated and correlated with their inhibition efficiencies (%IE). The inhibition effects of (PSCs) may be explained in terms of electronic properties. The results showed that the (%IE) of PSCs increased with the increase in EHOMO and decrease in ELUMO - EHOMO. The inhibitor molecules were first adsorbed on the iron surface and blocking the reaction sites available for corrosive attack; and the areas containing N and O atoms are most possible sites for bonding by donating electrons to the iron surface through interaction with π-electrons of the aromatic rings, and the azo methine group. Also, the adsorbed Schiff base molecules interact with iron ions in the corrosive media leading to neutral and cationic iron-Schiff base complexes. Adsorption process is spontaneous, exothermic and obeyed Temkin isotherm and regarded as physical as chemical mechanism. The polarization studied indicated that the inhibitors act as a mixed type inhibitor in HNO3; cause only inhibition of the cathode process in NaOH, and the magnitude of the displacement of the Tafel plot is proportional to its concentration. Models for the inhibition corrosion behaviour were developed based upon statistical analyses of the experimental data. Some thermodynamic and kinetic parameters (Kads, ΔGads) were estimated. Both experimental and quantum theoretical calculations are in excellent agreement. The inhibition efficiency increase in the order of: PSC_1 > PSC_2 > PSC_3 > PSC_4>PSC_5. Thus, DFT study gave further insight into the mechanism of inhibition action of PSCs. This research might provide a theoretical inhibition performance evaluation approach for homologous inhibitors.

A general scheme for systematically modeling long-range corrected ͑LC͒ hybrid density functionals is proposed. Our resulting two LC hybrid functionals are shown to be accurate in thermochemistry, kinetics, and noncovalent interactions, when compared with common hybrid density functionals. The qualitative failures of the commonly used hybrid density functionals in some "difficult problems," such as dissociation of symmetric radical cations and long-range charge-transfer excitations, are significantly reduced by the present LC hybrid density functionals.

The DDEC6 method is one of the most accurate and broadly applicable atomic population analysis methods. It works for a broad range of periodic and non-periodic materials with no magnetism, collinear magnetism, and non-collinear magnetism irrespective of the basis set type. First, we show DDEC6 charge partitioning to assign net atomic charges corresponds to solving a series of 14 Lagrangians in order. Then, we provide flow diagrams for overall DDEC6 analysis, spin partitioning, and bond order calculations. We wrote an OpenMP parallelized Fortran code to provide efficient computations. We show that by storing large arrays as shared variables in cache line friendly order, memory requirements are independent of the number of parallel computing cores and false sharing is minimized. We show that both total memory required and the computational time scale linearly with increasing numbers of atoms in the unit cell. Using the presently chosen uniform grids, computational times of ~9 to 94 seconds per atom were required to perform DDEC6 analysis on a single computing core in an Intel Xeon E5 multi-processor unit. Parallelization efficiencies were usually >50% for computations performed on 2 to 16 cores of a cache coherent node. As examples we study a B-DNA decamer, nickel metal, supercells of hexagonal ice crystals, six X@C60 endohedral fullerene complexes, a water dimer, a Mn 12-acetate single molecule magnet exhibiting collinear magnetism, a Fe4O12N4C40H52 single molecule magnet exhibiting non-collinear magnetism, and several spin states of an ozone molecule. Efficient parallel computation was achieved for systems containing as few as one and as many as >8000 atoms in a unit cell. We varied many calculation factors (e.g., grid spacing, code design, thread arrangement, etc.) and report their effects on calculation speed and precision. We make recommendations for excellent performance.

Aloe barbadensis (aloe-vera) also famous as a first aid plant is a valuable natural medicine. Its leaves have parallel venation that contains a soothing thick gel inside it and is useful for treatment and curing of wounds and diseases. In this paper, investigations were carried out to study the effect of dc and ac resistances of the aloe barbadensis leaves. The resistance of the leaf measured shows a proportional change with the change in the length of the leaf. The resistance of the leaf tissue increases with the increased distance between the electrodes due to circumvent current path. Both, fresh and the dry leaf of a aloe barbadensis plant was taken for the investigations. For fresh leaf, the dc resistance increases steeply along the length of a leaf while ac resistance comparatively shows a very slow increase in resistance, where as the results verified some fascinating changes in resistance as the leaf dried up.

The earth orbiting the sun, the electron bonded to a proton in the hydrogen atom are both manifestations of particles in motion bound by an inverse-square force and both are governed by the principle of least action (of all the possible paths the particles may take between two points in space and time, they take those paths for which the time integral of the Lagrangian or the difference, kinetic energy-potential energy, is the least) and shaped by the same Hamiltonian (or total energy) structure. For both types of motion, the invariants (or properties that are conserved) are the energy and angular momentum of the relative motion, and the symmetry is that of the rotational motion. Differences arise because the electric force bounding the electron to the proton is forty two orders of magnitude stronger than the gravitational force, and the smallness of the hydrogen atom brings about " quantum effects " : the mechanics of the microscopic particles which constitute the atom is wave-like. Yet the central concepts of mechanics are preserved in integrity: least action, invariants or conservation laws, symmetries, and the Hamiltonian structure. The discussion in the sections that follow on the quantum-mechanical treatment of molecular structures is based for the most part on the books by Pople and Murrell [2,3], and is by no means comprehensive but hopefully will elucidate the most relevant concepts for performing the estimation of thermochemical and kinetic properties of elementary reactions. The aim of quantum chemistry is to provide a qualitative and quantitative description of molecular structure and the chemical properties of molecules. The principal theories considered in quantum chemistry are valence bond theory and molecular orbital theory. Valence bond theory has been proven to be more difficult to apply and is seldom used, thus this discussion will deal only with the application of molecular orbital theory to molecular structures. In molecular orbital theory, the electrons belonging to the molecule are placed in orbitals that extend all the different nuclei making-up the molecule (the simplest approximation of a molecular orbital being a simple sum of the atomic orbitals with appropiate linear weighting coefficients, Figure 1 below for carbon Monoxide as example), in contrast to the approach of valence bond theory in which the orbitals are associated with the constituent atoms. The full analytical calculation of the molecular orbitals for most systems of interest may be reduced to a purely mathematical problem, the central feature of which is the calculation and diagonalization of an effective interaction energy matrix for the system. In ab initio molecular orbital calculations, the parameters that appear in such an energy matrix are exactly evaluated from theoretical considerations, while in semi-empirical methods experimental data on atoms and prototype molecular systems are used to approximate the atomic and molecular integrals entering the expression for the elements of the energy interaction matrix. Ab initio methods can be made as accurate as experiment for many purposes Zeener [4], the principal drawback to " high level " ab initio work is the cost in terms of computer resources which restrict it to systems of ten or fewer atoms even for the most experienced users. This is what draws the chemist to semi-empirical methods that can be easily applied to complex systems consisting of hundreds of atoms. Presently, useful semi-empirical methods are limited in execution by matrix multiplication and diagonalization, both requiring computer time proportional to N 3 where N is the number of atomic orbitals considered in the calculation or basis set.

A theoretical study of structures of the 1,7,1 l,17-tetraoxa-2,6,12,16-tetraaza-cycloeicosane ligand ([20] AneN 4 O 4) coordinated to Fe 2+ , Co 2+ , Ni 2+ , Ru 2+ , Rh 2+ , and Pd 2+ transition metals ions was carried out with the DFT/B3LYP method. Complexes were fully optimized in C s symmetry with the metal ions coordinated either to nitrogen (1a) or oxygen atoms (1b). For all the cases performed in this work, 1a was always more stable than 1b. Considering each row it is possible to see that the binding energy increases with the atomic number. The M 2+ cation binding energies increase in the following order: Fe 2+ <Ru 2+ <Co 2+ <Ni 2+ <Rh 2+ <Pd 2+. In addition, it was observed the preference of Pd 2+ and Rh 2+ complexes for a tetrahedral arrangement, while Fe 2+ , Ru 2+ , Co 2+ , Ni 2+ complexes had a preference for the octahedral arrangement. From the orbital representation results, it was seen that 1b unsymmetrical orbitals may influence the susceptibility over metal ions orientation toward heteroatoms orbitals.

Quantum  calculations  of  the  physical  properties  (electronic  and  vibrational),  based  on  density  functional  theory  (DFT) method at B3LYP/6-31G** level of theory, were performed, by means of the Gaussian 09 set of programs, to investigate the effect of the addition of the radical CN on pyridazine molecules. The best geometry, the total energy, frontier molecular orbital energies  (HOMO and HUMO),  energy  gap,  ionization  potential,  electron  affinity,  electronegativity,  chemical  hardness,  chemical  softness,  electrophilicity, dipole moment and the harmonic vibration frequencies were calculated and discussed for the study molecules. The electronic properties are computed by two different methods, a finite difference approximation and Koopman’s theorem. The study clearly shows that adding the radicals CN cause decreased the energy gap and the chemical hardness, and increase the electrophilicity. Therefore, the p resence of these  radicals  improves  the  conductivities  and  enhances  the  solubility  and  reactivity.  All  the  results  indicate  that  the  molecule 2,3-(CH) ₄N₂ (CN)2 is the best option for n-type organic semiconductors.

BeH is one of the most important benchmark systems for ab initio methods and for studying Born-Oppenheimer breakdown. However the best empirical potential and best ab initio potential for the ground electronic state to date give drastically different predictions in the long-range region beyond which measurements have been made, which is about ~1000 cm-1 for 9BeH, ~ 3000 cm-1 for 9BeD, and ~ 13000 cm-1 for 9BeT. Improved empirical potentials and Born-Oppenheimer breakdown corrections have now been built for the ground electronic states X(1^2 Sigma^+) of all three isotopologues. The predicted dissociation energy for 9BeH from the new empirical potential is now closer to the current best ab initio prediction by more than 66% of the discrepancy between the latter and the previous best empirical potential. The previous best empirical potential predicted the existence of unobserved vibrational levels for all three isotopologues, and the current best ab initio study also predicted the existence of all of these levels, and four more. The present empirical potential agrees with the ab initio prediction of all of these extra levels not predicted by the earlier empirical potential. With one exception, all energy spacings between vibrational energy levels for which measurements have been made, are predicted with an agreement of better than 1 cm^{-1} between the new empirical potential and the current best ab initio potential, but some predictions for unobserved levels are still in great disagreement, and the equilibrium bond lengths are different by orders of magnitude.

En el siguiente trabajo se utiliza el método Hartree Fock para el cálculo de energías de reacción, potencial de ionización y afinidad electrónica, analizando en cada caso que funciones permiten modelar mejor el sistema, teniendo en cuenta el principio variacional. Se consideran efectos como el error por superposición de base BBSE y el teorema de Koopmans. Dentro del estudio de los cambios energéticos, se observa que, aunque con el método es posible encontrar una base que modele bien cada sistema, se debe considerar el efecto de correlación electrónica.
Palabras clave: Principio variacional, BBSE, teorema de Koopmans, funciones base.

The influence of presence of counter ions and π-complexation with benzene on the bonding and
magnetic properties of Al4
2, the most studied all-metal cluster, is studied here. It is shown that
complexation by either counter ions or benzene decreases the delocalization index between
Al atoms and the magnitude of bond magnetizability, that is a Quantum Theory of Atoms in
Molecules, QTAIM, -based magnetic index of aromaticity. Benzene forms two types of π-complexes
with the Al4 framework; CH–π (T-shaped) complexes and parallel π–π stacking (PPS) complexes.
It is shown that variation in the p-charge of the Al4 framework affects the relative stability of the
T-shaped/PPS complexes. Free Al4
2 forms a stable T-shaped anion–π complex with benzene but
in the presence of cations, formation of PPS complexes is more favourable, energetically. It is
suggested that this property could be used for designing molecular switches and tuneable anion
sensors.

In an attempt to eradicate the challenges of fungi infections confronting Nigeria health sector by identification of novel anti-fungi agents, this study was embarked on to evaluate the antifungal activity of Garcinia kola seed against Candida albican, Aspergillus flaws, Fusarium oxysperium and Aspergilus niger using experimental and theoretical approaches. Garcinia kola seeds were bought from Okitipupa local market in Ondo State. It was authenticated, dehusked, sliced and air dried. The air dried sample was pulverized and extracted with methanol. The antifungal activity of the Garcinia kola seed extract at different concentrations were investigated using standard method. The zones of inhibition of the extract against test fungi ranges from 6 to 23mm while that of the control (amphotericin B) ranges from 17 to 29 mm. The broad spectrum of inhibition against test fungi exhibited by Garcinia kola seed revealed Garcinia kola seed as an important ingredient needed in pharmaceutical industry for the design of novel antifungal agent. The order of potency of Garcinia kola seed extract against test fungal at 75mg/ml was Candida albican, >Aspergilus niger > Aspergillus flaws > Fusarium oxysperium. Judging from the broad spectrum of inhibition and potency of Garcinia kola seed against test fungi, this study therefore ascertain Int. 42 that Garcinia kola seed could be used as a good therapeutic agent for the prevention or cure of fungi infections.

Net atomic charges (NACs) are widely used in all chemical sciences to concisely summarize key information about the partitioning of electrons among atoms in materials. The objective of this article is to develop an atomic population analysis method that is suitable to be used as a default method in quantum chemistry programs irrespective of the kind of basis sets employed. To address this challenge, we introduce a new atoms-in-materials method with the following nine properties: (1) exactly one electron distribution is assigned to each atom, (2) core electrons are assigned to the correct host atom, (3) NACs are formally independent of the basis set type because they are functionals of the total electron distribution, (4) the assigned atomic electron distributions give an efficiently converging polyatomic multipole expansion, (5) the assigned NACs usually follow Pauling scale electronegativity trends, (6) NACs for a particular element have good transferability among different conformations that are equivalently bonded, (7) the assigned NACs are chemically consistent with the assigned atomic spin moments, (8) the method has predictably rapid and robust convergence to a unique solution, and (9) the computational cost of charge partitioning scales linearly with increasing system size. We study numerous materials as examples: (a) a series of endohedral C 60 complexes, (b) high-pressure compressed sodium chloride crystals with unusual stoichiometries, (c) metal–organic frameworks, (d) large and small molecules, (e) organometallic complexes, (f) various solids, and (g) solid surfaces. Due to non-nuclear attractors, Bader's quantum chemical topology could not assign NACs for some of these materials. We show for the first time that the Iterative Hirshfeld and DDEC3 methods do not always converge to a unique solution independent of the initial guess, and this sometimes causes those methods to assign dramatically different NACs on symmetry-equivalent atoms. By using a fixed number of charge partitioning steps with well-defined reference ion charges, the DDEC6 method avoids this problem by always converging to a unique solution. These characteristics make the DDEC6 method ideally suited for use as a default charge assignment method in quantum chemistry programs.

Polarizabilities and London dispersion forces are important to many chemical processes. Force fields for classical atomistic simulations can be constructed using atom-in-material polarizabilities and C n (n ¼ 6, 8, 9, 10.) dispersion coefficients. This article addresses the key question of how to efficiently assign these parameters to constituent atoms in a material so that properties of the whole material are better reproduced. We develop a new set of scaling laws and computational algorithms (called MCLF) to do this in an accurate and computationally efficient manner across diverse material types. We introduce a conduction limit upper bound and m-scaling to describe the different behaviors of surface and buried atoms. We validate MCLF by comparing results to high-level benchmarks for isolated neutral and charged atoms, diverse diatomic molecules, various polyatomic molecules (e.g., polyacenes, fullerenes, and small organic and inorganic molecules), and dense solids (including metallic, covalent, and ionic). We also present results for the HIV reverse transcriptase enzyme complexed with an inhibitor molecule. MCLF provides the non-directionally screened polarizabilities required to construct force fields, the directionally-screened static polarizability tensor components and eigenvalues, and environmentally screened C 6 coefficients. Overall, MCLF has improved accuracy compared to the TS-SCS method. For TS-SCS, we compared charge partitioning methods and show DDEC6 partitioning yields more accurate results than Hirshfeld partitioning. MCLF also gives approximations for C 8 , C 9 , and C 10 dispersion coefficients and quantum Drude oscillator parameters. This method should find widespread applications to parameterize classical force fields and density functional theory (DFT) + dispersion methods.

Molecular structure, spectral investigation (1 H NMR, 13 C NMR, UV–Visible, FT-IR, FT-Raman), NBO, intramolecular hydrogen bonding, chemical reactivity and first hyperpolarizability analysis of formononetin [7-hydroxy-3(4-methoxyphenyl)chromone]: A quantum chemical study A combined theoretical and experimental approach is used to study the properties of formononetin. FT-Raman and FT-IR spectra were recorded in the solid phase, and interpreted in terms of PED analysis. The computational results diagnose the most stable conformer of formononetin. Chemical reactivity has been measured by reactivity descriptors and MEP. The existence of intramolecular H-bonds is investigated on the basis of AIM theory and NBO analysis. g r a p h i c a l a b s t r a c t a b s t r a c t Formononetin [7-hydroxy-3(4-methoxyphenyl)chromone or 4 0-methoxy daidzein] is a soy isoflavonoid that is found abundantly in traditional Chinese medicine Astragalus mongholicus (Bunge) and Trifolium pretense L. (red clover), and in an Indian medicinal plant, Butea (B.) monosperma. Crude extract of B. mono-sperma is used for rapid healing of fracture in Indian traditional medicine. In this study, a combined theoretical and experimental approach is used to study the properties of formononetin. The optimized geometry was calculated by B3LYP method using 6-311++G(d,p) as a large basis set. The FT-Raman and FT-IR spectra were recorded in the solid phase, and interpreted in terms of potential energy distribution (PED) analysis. Density functional theory (DFT) is applied to explore the nonlinear optical properties of the molecule. Good consistency is found between the calculated results and observed data for the electronic absorption, IR and Raman spectra. The solvent effects have been calculated using time-dependent density functional theory in combination with the integral equation formalism polarized continuum model, and the results are in good agreement with observed measurements. The double well potential energy curve of the molecule about the respective bonds, have been plotted, as obtained from DFT/6-31G basis set. The computational results diagnose the most stable conformer of formononetin. The HOMO–LUMO energy gap of possible conformers has been calculated for comparing their chemical activity. Chemical reactivity has been measured by reactivity descriptors and molecular electrostatic potential

We proposed and implemented a combined molecular dynamics and coordinate driving (MD/CD) method for automatically searching multistep reaction pathways of chemical reactions. In this approach, the molecular dynamic (MD) method at the molecular mechanics (MM) or semiempirical quantum mechanical (QM) level is employed to explore the conformational space of the minimum structures, and the modified coordinate driving (CD) method is used to build reaction pathways for representative conformers. The MD/CD method is first applied to two model reactions (the Claisen rearrangement and the intermolecular aldol reaction). By comparing the obtained results with those of the existing methods, we found that the MD/CD method has a comparable performance in searching low-energy reaction pathways. Then, the MD/CD method is further applied to investigate two reactions: the electrocyclic reaction of benzocyclobutene-7-carboxaldehyde and the intramolecular Diels−Alder reaction of ketothioester with 11 effectively rotatable single bonds. For the first reaction, our results can correctly account for its torquoselectivity. For the second one, our method predicts eight reaction channels, leading to eight different stereo-and regioselective products. The MD/CD method is expected to become an efficient and cost-effective theoretical tool for automatically searching low-energy reaction pathways for relatively complex chemical reactions.