ICHARG: Difference between revisions
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---- | ---- | ||
*{{TAG|ICHARG}}=0 | *{{TAG|ICHARG}}=0 | ||
:Calculate charge density from initial wave functions. | :Calculate the charge density from initial wave functions. | ||
:If {{TAG|ISTART}} is ''internally reset'' due to an invalid {{FILE|WAVECAR}} | :If {{TAG|ISTART}} is ''internally reset'' due to an invalid {{FILE|WAVECAR}} file, {{TAG|ICHARG}} will be set to {{TAG|ICHARG}}=2. | ||
*{{TAG|ICHARG}}=1 | *{{TAG|ICHARG}}=1 | ||
:Read the charge density from | :Read the charge density from {{FILE|CHGCAR}} file, and extrapolate from the old positions (on {{FILE|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 | :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 {{TAG|LMAXMIX}} are written. Upon restart, the energies might therefore differ slightly from the fully converged energies. The discrepancies can be large for the DFT+U method. In this case, one might need to increase {{TAG|LMAXMIX}} to 4 (d-elements) or even 6 (f-elements). | ||
*{{TAG|ICHARG}}=2 | *{{TAG|ICHARG}}=2 | ||
:Take superposition of atomic charge densities | :Take superposition of atomic charge densities. | ||
*{{TAG|ICHARG}}=4 | *{{TAG|ICHARG}}=4 | ||
: | :Read potential from file {{FILE|POT}}. The local potential on the file {{FILE|POT}} is written by the optimized-effective-potential methods (OEP), if the flag {{TAG|LVTOT}}=.TRUE. is supplied in the {{FILE|INCAR}} file. Supported as of VASP.5.1. | ||
*{{TAG|ICHARG}}+10 | *{{TAG|ICHARG}}+10 | ||
:non-selfconsistent calculations: Adding 10 to the value of {{TAG|ICHARG}}, e.g. {{TAG|ICHARG}}=11 or 12 (or the less convenient value 10) means that the charge density will be kept constant during the '' | :non-selfconsistent calculations: Adding 10 to the value of {{TAG|ICHARG}}, e.g., {{TAG|ICHARG}}=11 or 12 (or the less convenient value 10) means that the charge density will be kept constant during the ''entire electronic minimization''. | ||
:There are several reasons why to | :There are several reasons why to keep the charge density constant: | ||
:*{{TAG|ICHARG}}=11 | :*{{TAG|ICHARG}}=11 | ||
::To obtain the eigenvalues (for band structure plots) or the DOS | ::To obtain the eigenvalues (for band-structure plots) or the density of states (DOS) of a given charge density read from {{FILE|CHGCAR}}. The self-consistent {{FILE|CHGCAR}} file must be determined beforehand by a fully self-consistent calculation with a k-point grid spanning the entire Brillouin zone. | ||
:*{{TAG|ICHARG}}=12 | :*{{TAG|ICHARG}}=12 | ||
::Non-selfconsistent calculations for a superposition of atomic charge densities. This is in the spirit of the | ::Non-selfconsistent calculations for a superposition of atomic charge densities. This is in the spirit of the non-selfconsistent [[Harris Foulkes functional|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|Harris-Foulkes functional]]. | ||
{{NB|tip|If {{TAG|ICHARG}} is set to 11 or 12, it is strongly recommended to set {{TAG|LMAXMIX}} to twice the maximum l-quantum number in the pseudopotentials. Thus, for s and p elements {{TAG|LMAXMIX}} should be set to 2, for d elements {{TAG|LMAXMIX}} should be set to 4, and for f elements {{TAG|LMAXMIX}} should be set to 6.|:}} | |||
The initial charge density is of importance in the following cases: | |||
*If {{TAG|ICHARG}}≥10 the charge density remains constant during the run. | |||
*For all algorithms except {{TAG|IALGO}}=5X the initial charge density is used to set up the initial Hamiltonian that is used in the first few non-selfconsistent steps, c.f., {{TAG|NELMDL}} tag. | |||
== Related tags and articles == | |||
{{FILE|CHGCAR}}, {{TAG|ISTART}}, {{TAG|LCHARG}}, {{TAG|LMAXMIX}}, {{TAG|NELMDL}}, {{TAG|INIWAV}} | |||
{{sc|ICHARG|Examples|Examples that use this tag}} | {{sc|ICHARG|Examples|Examples that use this tag}} | ||
---- | ---- | ||
[[The_VASP_Manual|Contents]] | [[The_VASP_Manual|Contents]] | ||
[[Category:INCAR]][[Category:Electronic Minimization]][[Category:Charge Density]] | [[Category:INCAR]][[Category:Electronic Minimization]][[Category:Charge Density]] | ||
Revision as of 07:03, 29 March 2022
ICHARG = 0 | 1 | 2 | 4
| Default: ICHARG | = 2 | if ISTART=0 |
| = 0 | else |
Description: ICHARG determines how VASP constructs the initial charge density.
- ICHARG=0
- Calculate the 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 CHGCAR file, 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 DFT+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
- 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. Supported as of VASP.5.1.
- 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 entire electronic minimization.
- There are several reasons why to keep the charge density constant:
- ICHARG=11
- 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.
Tip: 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 4, 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 that is used in the first few non-selfconsistent steps, c.f., NELMDL tag.
Related tags and articles
CHGCAR, ISTART, LCHARG, LMAXMIX, NELMDL, INIWAV