Calculation of light absorption spectrum of Benzene $C_{6}H_{6}$ molecular using TDDFT.

TDDFT calculations in QE DO NOT support PAW.

You should go to Pseudo-dojo to download new PP.

We choose nc-sr-04/pbe/stringent/upf and then download.

STEP 1

Ionic relaxation.

 &CONTROL
    calculation = 'relax'
    prefix = 'C6H6'
    outdir = './outdir'
    pseudo_dir = '/BIGDATA1/ac_iphy_jrsun_1/soft/QE/pseudo_dojo'
    ! pseudo_dir = '/home/anonymous/quantumEspresso_2019/nc-sr-04_pbe_stringent_upf'
    etot_conv_thr = 1e-5
    forc_conv_thr = 1e-4
 /
 &SYSTEM
    ibrav = 6,
    celldm(1) = 32.0,
    celldm(3) = 0.83,
    nat = 12,
    ntyp = 2,
    ecutwfc = 30,
 /
 &ELECTRONS
    conv_thr =  1.0d-8
 /
 &IONS
 /

ATOMIC_SPECIES
 C  12.0107  C.upf
 H  1.00784  H.upf

ATOMIC_POSITIONS angstrom
C   5.633200899   6.320861303   5.000000000 1 1 0
C   6.847051545   8.422621957   5.000000000 1 1 0
C   8.060751351   7.721904557   5.000000000 1 1 0
C   8.060707879   6.320636665   5.000000000 1 1 0
C   6.846898786   5.620067381   5.000000000 1 1 0
C   5.633279551   7.722134449   5.000000000 1 1 0
H   6.847254360   9.512254789   5.000000000 1 1 0
H   9.004364510   8.266639340   5.000000000 1 1 0
H   9.004297495   5.775895755   5.000000000 1 1 0
H   6.846845929   4.530522778   5.000000000 1 1 0
H   4.689556006   5.776237709   5.000000000 1 1 0
H   4.689791688   8.267023318   5.000000000 1 1 0

K_POINTS gamma

New tags:

1. ibrav = 6:

ibrav = 6   Tetragonal P (st)   celldm(3)=c/a
      v1 = a(1,0,0),  v2 = a(0,1,0),  v3 = a(0,0,c/a)

and the unit is Bohr.
2. ecutwfc: if you use USPP, you should additionally set the ecutpho to be more than eight times the number of ecutwfc.

Result:

Begin final coordinates

ATOMIC_POSITIONS (angstrom)
C             5.6349072530        6.3219732663        5.0000000000    1   1   0
C             6.8471064692        8.4203756088        5.0000000000    1   1   0
C             8.0590688968        7.7208084975        5.0000000000    1   1   0
C             8.0589783279        6.3217775219        5.0000000000    1   1   0
C             6.8468944163        5.6223943554        5.0000000000    1   1   0
C             5.6350162132        7.7210074050        5.0000000000    1   1   0
H             6.8472239652        9.5241227823        5.0000000000    1   1   0
H             9.0149595312        8.2725861346        5.0000000000    1   1   0
H             9.0148270307        5.7699205361        5.0000000000    1   1   0
H             6.8468186394        4.5186488926        5.0000000000    1   1   0
H             4.6789926355        5.7702489027        5.0000000000    1   1   0
H             4.6792066205        8.2729360977        5.0000000000    1   1   0
End final coordinates

STEP 2

 &CONTROL
    calculation = 'scf'
    prefix = 'C6H6'
    outdir = './outdir'
    pseudo_dir = '/BIGDATA1/ac_iphy_jrsun_1/soft/QE/pseudo_dojo'
    ! pseudo_dir = '/home/anonymous/quantumEspresso_2019/nc-sr-04_pbe_stringent_upf'
 /
 &SYSTEM
    ibrav = 6,
    celldm(1) = 32.0,
    celldm(3) = 0.83,
    nat = 12,
    ntyp = 2,
    ecutwfc = 40,
    ecutrho = 320
 /
 &ELECTRONS
    conv_thr =  1.0d-10
 /

ATOMIC_SPECIES
 C  12.0107  C.upf
 H  1.00784  H.upf

ATOMIC_POSITIONS angstrom
C             5.6349072530        6.3219732663        5.0000000000    
C             6.8471064692        8.4203756088        5.0000000000    
C             8.0590688968        7.7208084975        5.0000000000    
C             8.0589783279        6.3217775219        5.0000000000   
C             6.8468944163        5.6223943554        5.0000000000    
C             5.6350162132        7.7210074050        5.0000000000    
H             6.8472239652        9.5241227823        5.0000000000   
H             9.0149595312        8.2725861346        5.0000000000    
H             9.0148270307        5.7699205361        5.0000000000    
H             6.8468186394        4.5186488926        5.0000000000    
H             4.6789926355        5.7702489027        5.0000000000    
H             4.6792066205        8.2729360977        5.0000000000    

K_POINTS gamma

STEP 3

TDDFT calculations.

Input file: C6H6.2_tl.in

&LR_INPUT
  prefix = 'C6H6'
  outdir = './outdir'
/

&LR_CONTROL
  itermax = 500 
  ipol = 4 
/

New tags:

1. itermax: Number of Lanczos iterations to be performed.
2. ipol： Determines the number of zeta coefficients to be calculated
   for a given polarization direction. 1 = x; 2 = y; 3 = z; 4 = x,y,z

Then we use yhbatch -N 1 -n 24 -p bigdata ./qe.sh turbo_lanczos.x

STEP 4

&LR_INPUT
  prefix = 'C6H6'
  outdir = './outdir'
  itermax0 = 500
  itermax = 10000
  extrapolation = 'osc'
  epsil = 0.01
  units = 1
  start = 0.0
  end = 50.0
  increment = 0.01
  ipol = 4
/

New Tags:

1. itermax0: Number of Lanczos coefficients to be read from the file. (Same with that of itermax in STEP 3)
2. itermax: The total number of Lanczos coefficients that will be considered in the calculation of the polarizability/absorption coefficient. If itermax > itermax0, the Lanczos coefficients in between itermax0+1 and itermax will be extrapolated.
3. extrapolation: Sets the extrapolation scheme. ‘osc’ = biconstant extrapolation, ‘constant’ = constant extrapolation and ‘no’ = no extrapolation.
4. epsil: The broadening/damping term (in Rydberg units).
5. units： The unit system used for the output and the start, end and increment input parameters.

   0 = Rydbergs, 1 = Electron volts and 2 = Nanometres per electron volts.

6. start/end: The polarizability and the absorption coefficient are computed starting from (/up to) this value.
7. increment: Incremental step used to define the mesh between start and end.
8. For the unit, the start/end/increment tag use the units set.

Then we use yhbatch -N 1 -n 24 -p bigdata ./qe.sh turbo_spectrum.x

We plot the C6H6.plot_S.data file: