LDIPOL: Difference between revisions

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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 in VASP. Can be applied for charged molecules and  molecules and slabs with a net dipole moment.
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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Due to the periodic boundary conditions, not only the total energy converges slowly with respect to the size of the supercell, but also the potential and the forces are affected by finite size errors. This effect can be counterbalanced by setting {{TAG|LDIPOL}}=.TRUE. in the {{FILE|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.
This is in the spirit of Neugebauer ''et al.''<ref name="Neugebauer92"/> (but more general and the total energy is correctly implemented, whereas the Neugebauer paper 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 groundstate might slow down considerably (''i.e.'', more electronic iterations might be required to obtain the required precision). It is recommended to use this mode only after pre-converging the orbitals without the {{TAG|LDIPOL}} flag, and the center of charge should be set in the {{FILE|INCAR}} file ({{TAG|DIPOL}}= center of mass). The user must also ensure that the cell is sufficiently large to determine the dipole moment with sufficient accuracy. If the cell is too small, charge might slash through the vacuum, causing very slow convergence (often convergence improves with the size of the supercell).


Restrictions: for charged systems, the potential correction is currently only implemented
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 cubic supercells. VASP will stop if the supercell is not cubic and {{TAG|LDIPOL}}=.TRUE.
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. }}


== Related Tags and Sections ==
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. }}
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== 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 ==
{{TAG|Monopole Dipole and Quadrupole corrections}},
{{TAG|Monopole Dipole and Quadrupole corrections}},
{{TAG|NELECT}},
{{TAG|NELECT}},
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== References ==
== References ==
<references>
<ref name="Neugebauer92">[http://dx.doi.org/10.1103/PhysRevB.46.16067 J. Neugebauer and M. Scheffler, Phys. Rev. B 46, 16067 (1992).]</ref>
</references>
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[[Category:INCAR]][[Category:Structural Optimization]][[Category:Forces]][[Category:Molecules]][[Category:Monopole Dipole and Quadrupole Corrections]]
 
[[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

Examples that use this tag

References

  1. ↑ a b J. Neugebauer and M. Scheffler, Phys. Rev. B 46, 16067 (1992).
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