LDIPOL: Difference between revisions
(refactor text - tips for convergence) |
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{{TAGDEF|LDIPOL|.TRUE. {{!}} .FALSE.|.FALSE.}} | {{TAGDEF|LDIPOL|.TRUE. {{!}} .FALSE.|.FALSE.}} | ||
Description: {{TAG|LDIPOL}} switches on corrections to the potential and forces | Description: {{TAG|LDIPOL}} switches on corrections to the potential and forces. Can be applied for charged molecules and slabs with a net dipole moment. | ||
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The presence of a dipole in combination with periodic boundary conditions leads to a slow convergence of the total energy with the size of the supercell. | |||
For {{TAG|LDIPOL}}=.TRUE., a linear correction, and for charged cells a quadratic electrostatic potential is added to the local potential in order to correct the errors introduced by the periodic boundary conditions. | Furthermore, finite-size errors affect the potential and the forces. | ||
This effect can be counterbalanced by setting {{TAG|LDIPOL}}=.TRUE. in the {{FILE|INCAR}} file. | |||
For {{TAG|LDIPOL}}=.TRUE., a linear correction, and for charged cells, a quadratic electrostatic potential is added to the local potential in order to correct the errors introduced by the periodic boundary conditions. | |||
{{NB|mind| This is in the spirit of Neugebauer ''et al.'' {{cite|neugebauer:prb:1992}}, though more general. Note that the total energy is correctly implemented, whereas Ref. {{cite|neugebauer:prb:1992}} contains an erroneous factor 2 in the total energy. }} | {{NB|mind| This is in the spirit of Neugebauer ''et al.'' {{cite|neugebauer:prb:1992}}, though more general. Note that the total energy is correctly implemented, whereas Ref. {{cite|neugebauer:prb:1992}} contains an erroneous factor 2 in the total energy. }} | ||
The biggest advantage of this mode is that leading errors in the forces are corrected and that the | The biggest advantage of this mode is that leading errors in the forces are corrected and that the work function can be evaluated for asymmetric slabs. The disadvantage is that the convergence to the electronic ground state might slow down considerably, i.e., more electronic iterations might be required to obtain the required precision. | ||
{{NB|warning| For charged systems, the potential correction is currently only implemented for cubic supercells. VASP will stop if the supercell is not cubic and {{TAG|LDIPOL}} is used. }} | {{NB|warning| For charged systems, the potential correction is currently only implemented for cubic supercells. VASP will stop if the supercell is not cubic and {{TAG|LDIPOL}} is used. }} | ||
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== Tips for improving convergence == | == Tips for improving convergence == | ||
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2. The center of charge should be set in the {{FILE|INCAR}} file ({{TAG|DIPOL}}= center of mass) | 2. The center of charge should be set in the {{FILE|INCAR}} file ({{TAG|DIPOL}}= center of mass) | ||
3. Ensure that the cell is sufficiently large to determine the dipole moment with sufficient accuracy (see {{TAG|DIPOL}}). If the cell is too small, the charge might slash through the vacuum, causing very slow convergence. Often convergence improves with the size of the supercell. | 3. Ensure that the cell is sufficiently large to determine the dipole moment with sufficient accuracy (see {{TAG|DIPOL}}). If the cell is too small, the charge might slash through the vacuum, causing very slow convergence. Often, convergence improves with the size of the supercell. | ||
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== Related tags and articles == | == Related tags and articles == | ||
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[[Category:INCAR tag]][[Category:Ionic minimization]][[Category:Forces]][[Category: | [[Category:INCAR tag]][[Category:Ionic minimization]][[Category:Forces]][[Category:Electrostatics]] | ||
Latest revision as of 13:33, 1 November 2023
LDIPOL = .TRUE. | .FALSE.
Default: LDIPOL = .FALSE.
Description: LDIPOL switches on corrections to the potential and forces. Can be applied for charged molecules and slabs with a net dipole moment.
The presence of a dipole in combination with periodic boundary conditions leads to a slow convergence of the total energy with the size of the supercell. Furthermore, finite-size errors affect the potential and the forces. This effect can be counterbalanced by setting LDIPOL=.TRUE. in the INCAR file. For LDIPOL=.TRUE., a linear correction, and for charged cells, a quadratic electrostatic potential is added to the local potential in order to correct the errors introduced by the periodic boundary conditions.
| Mind: This is in the spirit of Neugebauer et al. [1], though more general. Note that the total energy is correctly implemented, whereas Ref. [1] contains an erroneous factor 2 in the total energy. |
The biggest advantage of this mode is that leading errors in the forces are corrected and that the work function can be evaluated for asymmetric slabs. The disadvantage is that the convergence to the electronic ground state might slow down considerably, i.e., more electronic iterations might be required to obtain the required precision.
| Warning: For charged systems, the potential correction is currently only implemented for cubic supercells. VASP will stop if the supercell is not cubic and LDIPOL is used. |
Related tags and articles
Monopole Dipole and Quadrupole corrections, NELECT, EPSILON, IDIPOL, DIPOL, LMONO, EFIELD