LDIPOL: Difference between revisions
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Due to the periodic boundary conditions, not only the total energy converges slowly with respect to the size of the supercell, but | Due to the periodic boundary conditions, not only the total energy converges slowly with respect to the size of the supercell, but the potential and the forces are also affected by finite-size errors. 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. | 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. | ||
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 workfunction 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. }} | |||
== Tips for improving convergence == | |||
1. Use this mode only after pre-converging the orbitals without the {{TAG|LDIPOL}} tag | |||
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. | |||
== Related tags and articles == | == Related tags and articles == | ||
Revision as of 12:21, 18 October 2023
LDIPOL = .TRUE. | .FALSE.
Default: LDIPOL = .FALSE.
Description: LDIPOL switches on corrections to the potential and forces in VASP. Can be applied for charged molecules and molecules and slabs with a net dipole moment.
Due to the periodic boundary conditions, not only the total energy converges slowly with respect to the size of the supercell, but the potential and the forces are also affected by finite-size errors. 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 workfunction 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. |
Tips for improving convergence
1. Use this mode only after pre-converging the orbitals without the LDIPOL tag
2. The center of charge should be set in the INCAR file (DIPOL= center of mass)
3. Ensure that the cell is sufficiently large to determine the dipole moment with sufficient accuracy (see 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.
Related tags and articles
Monopole Dipole and Quadrupole corrections, NELECT, EPSILON, IDIPOL, DIPOL, LMONO, EFIELD