Input

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VASP basically needs 4 input files for standard production runs:

INCAR

The INCAR file holds the input parameters which "steer" the calculation.

• The default values set by VASP itself are a clever choice to do standard calculations.
• These standard settings can be modified to specify:
  • What do you want to do? (SCF calculation, DOS, dielectric properties ...)
  • You can give parameters to fulfill your requirements concerning required precision, requested convergence, calculation time ...

POSCAR

The POSCAR file contains the information on the structure.

• A simple POSCAR file may look like this:

fcc:  Ni
3.53
0.5 0.5 0.0
0.0 0.5 0.5
0.5 0.0 0.5
Ni
1
Selective Dyn
Cartesian
0 0 0  T T T

• The description of each line is given as follows:
  • 1: Header (comment).
  • 2: Overall scaling constant.
  • 3-6: Bravais matrix.
  • 4: Name(s) of the atom(s).
  • 5: Number of the atoms (of each atom type).
  • 6: (optional: selective dynamics).
  • 7: Specifies which coordinate system is used ("cartesian" or "direct").
  • 8-x: Positions of the atoms.

KPOINTS

The KPOINTS file determines the sampling of the 1st Brillouin zone.

• A typical KPOINTS file:

Automatic mesh
0
G (M)
4 4 4
0.  0.  0.

• The description of each line is given as follows:
  • 1: Header (comment).
  • 2: Specifies the k mesh generation type. $N_{\overrightarrow {k}}=0$: automatic generation scheme.
  • 3: $\Gamma$-centered (Monkhorst-Pack) grid.
  • 4: Number of subdivisions in each direction.
  • 5: Optional shift of the mesh.

POTCAR

The POTCAR file contains the relevant information concerning the pseudopotentials that are necessary to run the calculation:

• Data that was required for generating the pseudopotentials.
• Number of valence electrons.
• Atomic mass.
• Energy cut-off.

If the cell contains different atomic species, the corresponding POTCAR files have to be concatenated, in the same order as the atomic species are given in the POSCAR file.

N.B.: Different XC-types must not be mixed.

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