Up: The INCAR File
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ICHARG= 0 | 1 | 2 | 4
This flag determines how to construct the 'initial' charge density.
- Calculate charge density from initial orbitals.
Mind: if ISTART is
internally reset due to an invalid
WAVECAR-file the parameter ICHARG will be set to ICHARG=2.
- 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
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 6.63).
- Take superposition of atomic charge densities
- up from VASP.5.1 only: read potential from file POT
. The local potential
on the file POT is written by the optimized effective potential
if the flag LVTOT = .TRUE. is supplied
in the INCAR file.
- 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
There are several reasons why to use this flag:
If ICHARG is 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 4, and for f elements
LMAXMIX should be set to 6 (see section 6.63).
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.
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).
The initial charge density is of importance in the following cases:
- If ICHARG10 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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