# Explanations of input files (ground state of C2H2 molecule)

## required and recommened 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.

For isolated systems (specified by iperiodic = 0 in &system), the unit of 1/eV is used for the output files of DOS and PDOS if unit_system = 'A_eV_fs' is specified, while atomic unit is used if not. For other output files, the Angstrom/eV/fs units are used irrespective of the namelist value.

### &calculation

Mandatory: calc_mode

&calculation
calc_mode = 'GS'
/


This indicates that the ground state (GS) calculation is carried out in the present job. See Tutorial-v.1.0.0#&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
/


iperiodic = 0 indicates that the isolated boundary condition will be used in the calculation. al = 16d0, 16d0, 16d0 specifies the lengths of three sides of the rectangular parallelepiped where the grid points are prepared. nstate = 8 indicates the number of Kohn-Sham orbitals to be solved. nelec = 10 indicate the number of valence electrons in the system. Since the present code assumes that the system is spin saturated, nstate should be equal to or larger than nelec/2. nelem = 2 and natom = 4 indicate the number of elements and the number of atoms in the system, respectively. See Input variables#&system for more information.

### &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
/


Parameters related to atomic species and pseudopotentials. izatom(1) = 6 specifies the atomic number of the element #1. pseudo_file(1) = 'C_rps.dat' indicates the filename of the pseudopotential of element #1. lmax_ps(1) = 1 and lloc_ps(1) = 1 specify the maximum angular momentum of the pseudopotential projector and the angular momentum of the pseudopotential that will be treated as local, respectively.

### &rgrid

Mandatory: dl or num_rgrid

&rgrid
dl = 0.25d0, 0.25d0, 0.25d0
/


dl = 0.25d0, 0.25d0, 0.25d0 specifies the grid spacings in three Cartesian directions. See Input variables#&rgrid for more information.

### &scf

Mandatory: nscf

&scf
ncg = 4
nscf = 1000
convergence = 'norm_rho_dng'
threshold_norm_rho = 1.d-15
/


ncg is the number of CG iterations in solving the Khon-Sham equation. nscf is the number of scf iterations. For isolated systems specified by &system/iperiodic = 0, the scf loop in the ground state calculation ends before the number of the scf iterations reaches nscf, if a convergence criterion is satisfied. There are several options for the convergence check. If the value of norm_rho_dng is specified, the convergence is examined by the squared difference of the electron density,

### &analysis

The following namelists specify whether the output files are created or not after the calculation.

&analysis
out_psi = 'y'
out_dos = 'y'
out_pdos = 'y'
out_dns = 'y'
out_elf = 'y'
/


### &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.