The installation instructions are given at the end of this file.
The entire package ppp.tar.gz, in addition to this file (README), also
contains the following set of files:

I) Program files:

Total of 44 Fortran-90 Files

 ppp.f90
 bands.f90
 benperp.f90
 benzen.f90
 bond.f90
 c60_gen.f90
 ci_drv.f90
 delatm.f90
 delo_nlo.f90
 density.f90
 density_uhf.f90
 dipcal.f90
 dipint.f90
 dipmat.f90
 dipout.f90
 ecp.f90
 fockmat.f90
 fockmat_uhf.f90
 fourind.f90
 foutra_tb.f90
 ham_sci.f90
 matel.f90
 nlo.f90
 optics.f90
 orbden.f90
 printr.f90
 r_atom.f90
 read_ei.f90
 r_site.f90
 scf_rhf.f90
 scf_uhf.f90
 sci.f90
 spctrm_1ex.f90
 spctrm_a.f90
 stline.f90
 symsite.f90
 tij_gen.f90
 tij_readb.f90
 tij_read.f90
 twoind.f90
 vij_cal.f90
 write_1.f90
 write_2.f90
 writorb.f90


II) Choice of compiler:

  We have developed this program using the noncommercial version of
 the Intel Fortran compiler on the Linux operating system. Additionally,
 we have tested it using the gnu gfortran compiler. We expect it to work 
 with any Fortran 90 compiler. We are providing Makefiles both for Intel
 and gfortran compilers. We have not tested this program on the Windows
 operating system, but, we do not anticipate any problems.  
 

III) Libraries:

For the present program to work, it needs to link to LAPACK/BLAS libraries,
compiled with the same compiler which compiles this program. The location of
this library is specified by the variable LAPACK in the Makefile. For example,
with the Intel complier, we used the freely available ACML library of AMD,
Inc.  In case some other implementation 
of the library is used, the LAPACK variable in the Makefile should point to 
its location. Source files of LAPACK/BLAS library can be downloaded from
NETLIB (https://www.netlib.org), and then can be compiled using the 
compiler used for compiling our program. 

IV) Makefiles 

Makefile --- Makefile for PC based systems running linux and using
             Intel Fortran Compiler 
Makefile_gfort   -- Makefile for gfortran compiler 


V) Input preparation guide:

 Please read the file 'manual.pdf' (or 'manual.ps') 
 to understand how the input file is prepared for the program. 
 
 

VI) Input output files for example runs: 

The subdirectory 'Examples'  contains two subdirectories: (a) rhf and (b)
uhf. These sub-directories in turn contain example input and 
output files, corresponding to the restricted Hartree Fock and unrestricted 
Hartree Fock calculations discussed in the
paper. All the input files have extension .dat while the output ones have .out . 
Additionally some files with extension .xsf are there, which can be used to
visualize the system using the program XCrySDen. Moreover, there are  few more
files which are specialized outputs, described in the list below.


(A)rhf(subdirectory):

This subdirectory contains the following input files, and the corresponding
output files (with the extension .out). For example,

ppp8.dat   ---  Input file for total energy calculations of poly-para-phenylene with 
                eight repeat units.

ppp8.out   ---  Output file for total energy calculations of poly-para-phenylene with
                eight repeat units.
 
The convention we have adopted for naming the input files is system name, size of
the system, followed by the type of calculations. However, HF calculations and  
the standard parameters are taken as the genernal one and therefore, they are not 
specified in the filename, but in case of other type of calculations such as SCI 
or Hueckel model or calculations using screened (scr) parameters or something else, 
type of calculations is usually mentioned in the filename. 
    
For example, 
(i)   acene2_ciprep_orbden.dat => input file for oligoacene with two rings meant for
                                  performing just HF calculation, orbital density 
				  analysis, and generating output data for the subsequent 
				  correlated calculations.
		   
(ii)  tpa10_efield.dat => input file for a polyene with ten double bonds, HF
                          calculations were done in the presence of an external 
			  electric field.
			 
(iii) ppp8.dat => input file for HF calculations for oligo-PPP with eight repeat
                  units.
		   
(iv)  ppv8_scr.dat => input file for HF calculations using the screened
                      parameters for oligo-PPV with eight repeat units.	   			 
                                                                               
 The input files in this subdirectory are
                             
acene2_ciprep_orbden.dat -- HF calculations + orbital density analysis + generation 
                            of output data for the subsequent correlated calculations
tpa10.dat -- HF calculations
tpa10_efield.dat -- Calculations in the presence of electric field
tpa10_sci.dat -- Single CI calculations to be performed
tpa10_nlo.dat -- HF calculations + generation of output data for the subsequent 
                 nonlinear optical properties calculations
tpa10_ciprep.dat -- HF calculations + generation of output data for the 
                    subsequent correlated calculations
tpa11.dat -- HF calculations
ppv8.dat -- HF calculations using the standard parameters
ppv8_scr.dat -- HF calculations using the screened parameters
ppp8.dat -- HF calculations 
ppp_band.dat -- Band structure calculations using the Hueckel model
ppp8_hueckel_linear_absorption.dat -- Linear optical absorption spectrum at the
                                      tight binding level
ppp8_hf_linear_absorption.dat -- Linear optical absorption spectrum at the
                                 HF level
ppp8_sci_linear_absorption.dat -- Linear optical absorption spectrum at the
                                  SCI level
ppp8_sci_linear_absorption_ef0.001.dat -- Linear optical absorption spectrum at the
                                          SCI level in the presence of electric
					  field
ppp8_sci_scr_linear_absorption.dat -- Linear optical absorption spectrum at the
                                      SCI level using the screened parameters


Apart from the above mentioned input and their correponding output files,
following additional specialized files are also there in the directory:

spec001_ppp8_hueckel_linear_absorption.dat -- linear optical absorption spectrum for PPP-8 using Hueckel model 
spec001_ppp8_hf_linear_absorption.dat -- linear optical absorption spectrum for PPP-8 at HF level, using P-P-P model
spec001_ppp8_sci_linear_absorption.dat -- linear optical absorption spectrum for PPP-8 at SCI level, using P-P-P model
spec001_ppp8_sci_linear_absorption_ef0.001.dat -- linear optical absorption spectrum computed in the presence of an external 
                                                  electric field of 0.001 V/Angstrom for PPP-8 at SCI level, using P-P-P model
spec001_ppp8_sci_scr_linear_absorption.dat -- linear optical absorption spectrum computed using screened parameters in the P-P-P 
                                              model Hamiltonian, for PPP-8, at SCI level
ppp_band_structure.plt -- band structure plot for PPP
acene2_strc.xsf -- XCrySDen input file for the structure of acene2
ppp8_strc.xsf -- XCrySDen input file for the structure of PPP-8
ppv8_strc.xsf -- XCrySDen input file for the structure of PPV-8
tpa11_strc.xsf -- XCrySDen input file for the structure of t-PA with 11 repeat units


(B) uhf subdirectory:

This subdirectory contains the following input files, and the corresponding
output files (with the extension .out). Additionally some files with extension .xsf are there, which can be used to
visualize the system using the program XCrySDen. As the name of the subdirectory 
indicates, the files inside it use unrestricted Hartree Fock method for the calculations.

This subdirecory contains some sample input and structure (.xsf) files listed bellow.

trigonal_zigzag_benzo3_uhf.dat -- UHF calculations for the system containing odd number of electrons
trigonal_zigzag_benzo3_uhf_efield.dat -- UHF calculations in the presence of an external electric field
trigonal_zigzag_benzo3_uhf_scr.dat -- UHF calculations using screened parameters
trigonal_zigzag_benzo6_uhf.dat -- UHF calcualtions for the system containing even number of electrons
trigonal_zigzag_benzo3_strc.xsf -- structure file for the trigonal zigzag graphene nanodisk with three
                                   benzene rings
trigonal_zigzag_benzo6_strc.xsf -- structure file for the trigonal zigzag graphene nanodisk with six 
                                   benzene rings

Installation Instructions:

  i) Untar and unzip the archive ppp.tar.gz.

  ii) Make sure that your default directory has a subdirectory bin. It should
      also be in your path.

  iii) Install some version of the LAPACK/BLAS libraries. Either obtain the
       noncommercial versions from AMD or INTEL, or download the source code
       from www.netlib.org, and compile and install those libraries using the
       compiler which you intend to use to compile ppp.x on your system. 

  iv) Modify the makefiles provided with this program so that it will compile
      with the LAPACK/BLAS libraries installed in step (iii).

   v) To compile the ppp.x program, enter subdirectory src and then

      a) type 'make' if you want to use the intel Fortran compiler
                  
                OR   

      b) type 'make -f Makefile_gfort' if you want to use the GNU gfortran
         compiler.

     If the compilation is successful, your bin directory will contain
     the program ppp.x.


  vi) To test the program go to a subdirectory (rhf or uhf) of the 
      directory Examples 
      

    In case you want to test the HF calculation for naphthalene using
    the RHF method, issue command

    ppp.x < ppv8.dat > x.out 

    Upon completion of the program, compare the contents of x.out to
    the file ppv8.out. They should be very similar to each other.