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ICHARG = 0 | 1 | 2 | 4
|Default: ICHARG||= 2||if ISTART=0|
Description: ICHARG determines how VASP constructs the initial charge density.
- 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.
- 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).
- Take superposition of atomic charge densities
- 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.
- 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:
- 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 pseudopotentials. 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.