ICHARG-tag

$$ICHARG = 0 \vert 1 \vert 2 \vert 4$$

Default:
if ISTART=0	2
else	0

This flag determines how to construct the 'initial' charge density.

0

Calculate charge density from initial wave functions.

Mind: if ISTART is internally reset due to an invalid WAVECAR-file the parameter ICHARGwill be set to ICHARG=2.

1

Read the charge density from file CHGCAR, and extrapolate from the old positions (on CHCGAR) to the new positions using a linear combination of atomic charge densities. In the PAW method, there is however one important point to keep in mind. For the on-site densities (that is the densities within the PAW sphere) only l-decomposed charge densities up to LMAXMIX are written. Upon restart the energies might therefore differ slightly from the fully converged energies. The discrepancies can be large for the L(S)AD+U method. In this case, one might need to increase LMAXMIX to 4 (d-elements) or even 6 (f-elements) (see Section 6.56).

2

Take superposition of atomic charge densities

4

VASP.5.1 only: read potential from file POT. The local potential on the file POT is written by the optimized effective potential methods (OEP), if the flag LVTOT=.TRUE. is supplied in the INCAR file.

+10

non-selfconsistent calculation

Adding ten to the value of ICHARG(e.g. using 11,12 or the less convenient value 10) means that the charge density will be kept constant during the whole electronic minimization.

There are several reasons why to use this flag:

• ICHARG=11: To obtain the eigenvalues (for band structure plots) or the DOS for a given charge density read from CHGCAR. The selfconsistent CHGCAR file must be determined beforehand doing by a fully selfconsistent calculation with a k-point grid spanning the entire Brillouin zone.9.3.

• ICHARG=12: Non-selfconsistent calculations for a superposition of atomic charge densities. This is in the spirit of the non-selfconsistent Harris-Foulkes functional. The stress and the forces calculated by VASP are correct, and it is absolutely possible to perform an ab-initio MD for the non-selfconsistent Harris-Foulkes functional (see section 7.3).

If ICHARGist set to 11 or 12, it is strongly recommened to set LMAXMIX to twice the maximum l-quantum number in the pseudpotentials. Thus for s and p elements LMAXMIX should be set to 2, for d elements LMAXMIX should be set to 2, and for f elements LMAXMIX should be set to 6 (see section 6.56).

The initial charge density is of importance in the following cases:

• If ICHARG$>$10 the charge density remains constant during the run.
• For all algorithms except IALGO=5X the initial charge density is used to set up the initial Hamiltonian which is used in the first few (NELMDL) non selfconsistent steps.