ICHARG: Difference between revisions
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{{TAGDEF|ICHARG|0 {{!}} 1 {{!}} 2 {{!}} 4}} | {{TAGDEF|ICHARG|0 {{!}} 1 {{!}} 2 {{!}} 4 {{!}} 5}} | ||
{{DEF|ICHARG|2|if {{TAG|ISTART}}{{=}}0|0|else}} | {{DEF|ICHARG|2|if {{TAG|ISTART}}{{=}}0|0|else}} | ||
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*{{TAG|ICHARG}}=1 | *{{TAG|ICHARG}}=1 | ||
: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. | :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: 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). | :In the [[Projector-augmented-wave_formalism|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). | ||
{{NB|tip|To improve convergence and reduce the number of electronic steps, it is recommended to set ICHARG {{=}} 1 when starting calculations repeatedly with small changes in the input parameters.|:}} | |||
*{{TAG|ICHARG}}=2 | *{{TAG|ICHARG}}=2 | ||
:Take superposition of atomic charge densities. | :Take superposition of atomic charge densities. | ||
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: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. | :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}}=5 | ||
:External charge-density-update mode to read in and add an external correction to the Kohn-Sham (KS) occupations in every SCF step of the [[electronic minimization]]. The initialization of the charge density is done as in {{TAG|ICHARG}}=1, and after {{TAG|NELMDL}} steps VASP reads the occupations from a user-supplied text file {{FILE|GAMMA}} for each k point in each SCF step. The procedure described in Ref.{{cite|schueler:jpcm:30}} Eq. (30)-(32) is then used to construct a new charge density from the combined occupations (KS occupations + {{FILE|GAMMA}} file), from which the next KS potential is constructed. The [[electronic minimization|DFT workflow]] continues after a user-supplied {{FILE|vasp.lock}} file is read. Additionally, with {{TAG|ICHARG}}=5 after each SCF step VASP writes out all with {{TAG|LOCPROJ}} defined wave function projections. The {{TAG|ICHARG}}=5 mode can be used with an external code that modifies the occupations, and requires extra output after each SCF step. The TRIQS software package{{cite|parcollet:cpc:196}} makes use of it to perform charge self-consistent DFT plus dynamical mean field theory (DMFT) calculations{{cite|merkel:joss:7}}{{cite|aichhorn:cpc:204}}, and provides tutorials on how to perform such calculations with VASP{{cite|triqsdfttoolstutorial:web}}{{cite|soliddmfttutorial:web}}. | |||
*{{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 ''entire electronic minimization''. | :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''. | ||
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:*{{TAG|ICHARG}}=12 | :*{{TAG|ICHARG}}=12 | ||
::Non-self-consistent calculations for a superposition of atomic charge densities. This is in the spirit of the non-self-consistent [[Harris-Foulkes functional|Harris-Foulkes functional]]. The stress and the forces calculated by VASP are correct, and it is | ::Non-self-consistent calculations for a superposition of atomic charge densities. This is in the spirit of the non-self-consistent [[Harris-Foulkes functional|Harris-Foulkes functional]]. The stress and the forces calculated by VASP are correct, and it is 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.|:}} | {{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.|:}} | ||
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== Related tags and articles == | == Related tags and articles == | ||
{{FILE|CHGCAR}}, {{TAG|ISTART}}, {{TAG|LCHARG}}, {{TAG|LMAXMIX}}, {{TAG|NELMDL}}, {{TAG|INIWAV}} | {{FILE|CHGCAR}}, {{TAG|ISTART}}, {{TAG|LCHARG}}, {{TAG|LMAXMIX}}, {{TAG|NELMDL}}, {{TAG|INIWAV}}, {{FILE|GAMMA}} | ||
{{sc|ICHARG|Examples|Examples that use this tag}} | {{sc|ICHARG|Examples|Examples that use this tag}} | ||
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---- | ---- | ||
[[Category:INCAR tag]][[Category:Electronic minimization]][[Category:Charge density]] | [[Category:INCAR tag]][[Category:Electronic minimization]][[Category:Electronic ground-state properties]][[Category:Charge density]][[Category:Electronic occupancy]] | ||
Latest revision as of 07:36, 18 October 2024
ICHARG = 0 | 1 | 2 | 4 | 5
| 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).
Tip: To improve convergence and reduce the number of electronic steps, it is recommended to set ICHARG = 1 when starting calculations repeatedly with small changes in the input parameters.
- 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=5
- External charge-density-update mode to read in and add an external correction to the Kohn-Sham (KS) occupations in every SCF step of the electronic minimization. The initialization of the charge density is done as in ICHARG=1, and after NELMDL steps VASP reads the occupations from a user-supplied text file GAMMA for each k point in each SCF step. The procedure described in Ref.[1] Eq. (30)-(32) is then used to construct a new charge density from the combined occupations (KS occupations + GAMMA file), from which the next KS potential is constructed. The DFT workflow continues after a user-supplied vasp.lock file is read. Additionally, with ICHARG=5 after each SCF step VASP writes out all with LOCPROJ defined wave function projections. The ICHARG=5 mode can be used with an external code that modifies the occupations, and requires extra output after each SCF step. The TRIQS software package[2] makes use of it to perform charge self-consistent DFT plus dynamical mean field theory (DMFT) calculations[3][4], and provides tutorials on how to perform such calculations with VASP[5][6].
- 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-self-consistent calculations for a superposition of atomic charge densities. This is in the spirit of the non-self-consistent Harris-Foulkes functional. The stress and the forces calculated by VASP are correct, and it is 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, GAMMA
- ↑ M. Schüler, O. E. Peil, G. J. Kraberger, R. Pordzik, M. Marsman, G. Kresse, T. O. Wehling, and M. Aichhorn, Journal of Physics: Condensed Matter 30, 475901 (2018).
- ↑ O. Parcollet, M. Ferrero, T. Ayral, H. Hafermann, I. Krivenko, L. Messio and P. Seth, Computer Physics Communications 196, 398 (2015).
- ↑ M. E. Merkel, A. Carta, S. Beck and Alexander Hampel, Journal of Open Source Software 7, 77 (2022).
- ↑ M. Aichhorn, L. Pourovskii, P. Seth, V. Vildosola, M. Zingl, O. E. Peil, X. Deng, J. Mravlje, G. J. Kraberger, C. Martins, M. Ferrero, O. Parcollet, Computer Physics Communications 204, 200 (2016).
- ↑ triqs.github.io/dft_tools/latest/tutorials.html#vasp-interface-examples (2024).
- ↑ triqs.github.io/solid_dmft/tutorials/PrNiO3_csc_vasp_plo_cthyb/tutorial (2024).