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Real-time time dependent density functional theory

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Real-time time dependent density functional theory (rt-TDDFT) approaches, directly provide time domain evolution of electronic wave functions together with ionic movements, presenting a versatile way for the real time tracking of ultrafast dynamics and phenomena either in perturbative or non-perturbative regime.

To run Real-time TDDFT (Time-Dependent DFT) simulations with ABACUS, the KPT file and the STRU file should be set in the same way as in Sec. 4.7. A typical INPUT file for TDDFT simulation is given below, which contains additional keywords that need to be added.

INPUT_PARAMETERS
#Parameters (General)
pseudo_dir ./
ntype 1
nbands 12
calculation md

#Parameter (Accuracy)
ecutwfc 50
scf_nmax 30
smearing_method gaussian
smearing_sigma 0.02
basis_type lcao
out_chg 1
gamma_only 0
md_nstep 2000
scf_thr 1.0e-6
md_type 0
md_dt 0.01
md_tfirst 30
md_restart 0
md_tlast 30
md_dumpfreq 1
tddft 1
init_vel 1
ocp 1
ocp_set 6*2 6*0
val_elec_01 5
vext 1
vext_dire 2

Note: The TDDFT simulation is based on molecular dynamics in ABACUS. Accomplished with these MD parameters, TDDFT needs some new key words. The TDDFT simulation can be calculated only in lcao bases.

  • tddft : 1, calculate TDDFT; 0, no calculate TDDFT.
  • init_vel : 1, set the initial velocities of the atoms in STRU; 0, do not set the initial velocities.
  • ocp : 1, set initial occupations ; 0 , do not set initial occupations.
  • ocp_set : occupations multiplies the number of the bands. For example, 62 60 means that the occupations of the lower 6 bands are 2 and the occupations of the higer 6 bands are 0.
  • vext : 1, a laser material interaction is included; 0, no extern laser field.
  • vext_dire : 1, 2, 3, the direction of the extern laser field added x, y, z. The results of the TDDFT calculation are dependent on what you want. Dynamics, High-order harmonic generation and occupation could be achieved when you do TDDFT calculation. Users can also do some post-processing according to the basic TDDFT calculation.

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