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# Input

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:
• 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.

```Automatic mesh
0
G (M)
4 4 4
0.  0.  0.
```
• The description of each line is given as follows:
• 2: Specifies the k mesh generation type. ${\displaystyle N_{\overrightarrow {k}}=0}$: automatic generation scheme.
• 3: ${\displaystyle \Gamma }$-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 pseudo potentials that are necessary to run the calculation:

• Data that was required for generating the pseudo potentials.
• 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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