# Explanations of input files (polarizability and photoabsorption of C2H2 molecule)

## required and recommended variables

### &units

Mandatory: none

&units
unit_system='A_eV_fs'
/


This namelist specifies the unit system to be used in the input file. If you do not specify it, atomic unit will be used. See Input variables#&units for detail.

### &calculation

Mandatory: calc_mode

&calculation
calc_mode = 'RT'
/


This indicates that the real time (RT) calculation is carried out in the present job. See Input variables#&calculation for detail.

### &control

Mandatory: none

&control
sysname = 'C2H2'
/


'C2H2' defined by sysname = 'C2H2' will be used in the filenames of output files.

### &system

Mandatory: iperiodic, al, nstate, nelem, natom

&system
iperiodic = 0
al = 16d0, 16d0, 16d0
nstate = 5
nelem = 2
natom = 4
nelec = 10
/


These namelists and their values should be the same as those used in the ground state calculation. See Explanations of input files (ground state of C2H2 molecule)#&system.

### &pseudo

Mandatory: pseudo_file, izatom

&pseudo
izatom(1)=6
izatom(2)=1
pseudo_file(1)='C_rps.dat'
pseudo_file(2)='H_rps.dat'
lmax_ps(1)=1
lmax_ps(2)=0
lloc_ps(1)=1
lloc_ps(2)=0
/


These namelists and their values should be the same as those used in the ground state calculation. See Explanations of input files (ground state of C2H2 molecule)#&pseudo.

### &tgrid

Mandatory: dt, Nt

&tgrid
dt=1.25d-3
nt=5000
/


dt=1.25d-3 specifies the time step of the time evolution calculation. nt=5000 specifies the number of time steps in the calculation.

### &emfield

Mandatory: ae_shape1

&emfield
ae_shape1 = 'impulse'
epdir_re1 = 0.d0,0.d0,1.d0
/


ae_shape1 = 'impulse' indicates that a weak impulse is applied to all electrons at t=0 epdir_re1(3) specify a unit vector that indicates the direction of the impulse. See Input variables#&emfield for details.

### &atomic_coor

Mandatory: atomic_coor or atomic_red_coor (it may be provided as a separate file)

&atomic_coor
'C'    0.000000    0.000000    0.599672  1
'H'    0.000000    0.000000    1.662257  2
'C'    0.000000    0.000000   -0.599672  1
'H'    0.000000    0.000000   -1.662257  2
/


Cartesian coordinates of atoms. The first column indicates the element. Next three columns specify Cartesian coordinates of the atoms. The number in the last column labels the element. They must be the same as those in the ground state calculation.