ICHARG

ICHARG = 0 | 1 | 2 | 4 

Default: ICHARG	= 2	if ISTART=0
	= 0	else

Description: ICHARG determines how VASP constructs the initial charge density. an equation array

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• ICHARG=0

Calculate charge density from initial wave functions.

If ISTART is internally reset due to an invalid WAVECAR-file ICHARG will be set to ICHARG=2.

• ICHARG=1

Read the charge density from file CHGCAR, and extrapolate from the old positions (on CHGCAR) 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)DA+U method. In this case, one might need to increase LMAXMIX to 4 (d-elements) or even 6 (f-elements).

• ICHARG=2

Take superposition of atomic charge densities

• ICHARG=4

Supported as of VASP.5.1: 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.

• ICHARG+10

non-selfconsistent calculations: Adding 10 to the value of ICHARG, e.g. ICHARG=11 or 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 self-consistent calculation with a k-point grid spanning the entire Brillouin zone.\ref{ex-band}.

• 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.

If ICHARG is set to 11 or 12, it is strongly recommended 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.

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.

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