Calculation of atoms

The following files are needed for the calculation of atoms

• INCAR
• POSCAR
• POTCAR
• KPOINTS

Before using a pseudopotential intensively it is not only necessary to check it in different bulk phases but the pseudopotential should also reproduce exactly the eigenvalues and the total energy of the free atom for which it was created. If energy cutoff and cell size are sufficient, the agreement between the atomic reference calculation and a calculation using VASP is normally better than 1 meV. Calculations for an atom are relatively fast and unproblematic in most cases.

For the calculation only the $\Gamma$ point should be used i.e. the KPOINTS file should have the following contents:

Monkhorst Pack
0
Monkhorst Pack
 1  1  1
 0  0  0

The size of the cell depends on the element in question. Some values for reliable results are compiled in Tab. 1.

Tab. 1: Typical convenient settings for the cellsize for a calculation of atoms.

	Cellsize
Aluminum	14 $\mathrm {\AA}$
Potassium	12 $\mathrm {\AA}$
Copper, Rhodium, Palldium ...	10 $\mathrm {\AA}$
Nitrogen	7 $\mathrm {\AA}$
Carbon	8 $\mathrm {\AA}$

A simple cubic cell can be often enough but it is usually recommended to use nearly cubic cells with minimal orthorombic distortion. This can be important for some atoms due to higher degrees of freedom for relaxation. An example POSCAR file should look like:

atom
1
     10.00000    .00000    .00000
       .00000  10.00100    .00000
       .00000    .00000  10.00200
   1
cart
 0    0    0

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