Crystalline Si example

By using silicon in the diamond structure an example, short description on the basic input variables for solid is provided here.

nfinp_scf:

#
# Crystalline silicon in the diamond structure
#
WF_OPT    DAV
NTYP      1
NATM      2
TYPE      2
NSPG      227
GMAX      4.00
GMAXP     8.00
KPOINT_MESH    8   8   8
KPOINT_SHIFT   OFF OFF OFF
WIDTH     0.0002
EDELTA    0.5000D-09
NEG    8
CELL   10.30  10.30  10.30  90.00  90.00  90.00
&ATOMIC_SPECIES
 Si 28.0900 pot.Si_pbe1
&END
&ATOMIC_COORDINATES CRYSTAL
      0.000000000000      0.000000000000      0.000000000000    1    1    1
      0.250000000000      0.250000000000      0.250000000000    1    1    1
&END

Each input variables and blocks (&[BLOCK_NAME] … &) are explained below:

WF_OPT    DAV

WF_OPT is used to specify the wave function method. Default is DAV.

NTYP      1

NTYP defines the number of atomic species in the system.

NATM      2

NATM defines the number of atoms in the unit cell.

TYPE      2

TYPE defines the Bravis lattice 2 is for the face centered cubic. Default is 0 (Simple lattice).

NSPG      227

NSPG is the space group number. Default is 1. Note not all the space group operations are implemented.

GMAX      4.00

GMAX is the cutoff wave vector for the plane wave expansion of the wave functions. GMAX**2 corresponds to the cutoff energy in Rydberg.

GMAXP     8.00

GMAXP is the cutoff wave vector for the plane wave expansion of charge density. GMAXP**2 corresponds to the cutoff energy in Rydberg. When only the normconserving pseudopotentials are used, GMAXP should be twice as GMAX and can be omitted.

KPOINT_MESH    8   8   8

KPOINT_MESH is used to define the k-point mesh for the Brillouin zone sampling.

KPOINT_SHIFT   OFF OFF OFF

KPOINT_SHIFT is used to specify if the k-point is shifted or not. If shifted, the Gamma-point is _not_ included in the k-point set.

WIDTH     0.0002

WIDTH is the width of the broadening (in Hartree) to approximate the delta function. For systems with a gap, very small positive WIDTH is used. In such a case, it does not have a physical meaning and is used to determine the Fermi level.

EDELTA    0.5000D-09

EDELTA is the convergence threshold for the total energy in Hartree per atom for the SCF calculation.

NEG    8

NEG is the number of states/bands considered in the calculation. STATE does not allow an occupied-state only calculation, and therefore NEG should be large enough to include occupied states and some unoccupied states.

CELL   10.30  10.30  10.30  90.00  90.00  90.00

CELL defines the cell parameter \(a\), \(b\), \(c\), \(\alpha\), \(\beta\), and \(\gamma\), where \(a\), \(b\), \(c\), are the lengths (in Bohr) of the 1st, 2nd, and 3rd lattice vectors, respectively, and \(\alpha\), \(\beta\), and \(\gamma\), are the angles (in degree) between 2nd and 3rd, 3rd and 1st, and 1st and 2nd lattice vectors, respectively.

&ATOMIC_SPECIES
 Si 28.0900 pot.Si_pbe1
&END

The block &ATOMIC_SPECIES ... &END is used to define the atomic types. The syntax is similar to the one in Quantum-ESPRESSO.

Syntax:

&ATOMIC_SPECIES
 ATOMIC_NUMBER(1) ATOMIC_MASS(1) PSEUDOPOTENTIAL_FILE(1)
 ATOMIC_NUMBER(2) ATOMIC_MASS(2) PSEUDOPOTENTIAL_FILE(2)
 ...
 ATOMIC_NUMBER(NTYP) ATOMIC_MASS(NTYP) PSEUDOPOTENTIAL_FILE(NTYP)
&END

or:

&ATOMIC_SPECIES
 ATOMIC_SYMBOL(1) ATOMIC_MASS(1) PSEUDOPOTENTIAL_FILE(1)
 ATOMIC_SYMBOL(2) ATOMIC_MASS(2) PSEUDOPOTENTIAL_FILE(2)
 ...
 ATOMIC_SYMBOL(NTYP) ATOMIC_MASS(NTYP) PSEUDOPOTENTIAL_FILE(NTYP)
&END

where NTYP is the number of atomic species.

&ATOMIC_COORDINATES CRYSTAL
      0.000000000000      0.000000000000      0.000000000000    1    1    1
      0.250000000000      0.250000000000      0.250000000000    1    1    1
&END

The block &ATOMIC_COORDINATES ... &END is used to define the atomic coordinates in the legacy STATE format.

Syntax:
&ATOMIC_COORDINATES [CRYSTAL|CRYS|CARTESIAN|CART]
 CPS(1,1) CPS(1,2) CPS(1,3) IWEI(1) IMDTYP(1) ITYP(1)
 CPS(2,1) CPS(2,2) CPS(2,3) IWEI(2) IMDTYP(2) ITYP(2)
 ...
 CPS(NATM,1) CPS(NATM,2) CPS(NATM,3) IWEI(NATM) IMDTYP(NATM) ITYP(NATM)
&END
CARTESIAN/CART: If set, atomic coordinates are given in the cartesian coordinate

CRYSTAL/CRYS: If set, atomic coordinates are given in the crystal coordinate

CPS: Atomic coordinate in the cartesian (NCORD=1 or COORD=CARTESIAN) or in the crystal (NCORD=0 or COORD=CRYSTAL) coordinate

IWEI: number of equivalent atoms under the inversion symmetry (currently inversion symmetry is disabled and always IWEI is always set to 1).

IMDTYP:

1: Allow to move the ion

0: Fix the ion

Default coordinate system is CARTESIAN. This is chosen when &ATOMIC_COORDINATES without argument is used.