Monopole Dipole and Quadrupole Corrections

For charged cells or for calculations of molecules and surfaces with a large dipole moment, the energy converges very slowly with respect to the size $L$ of the supercell. Using methods discussed by Makov et al. and Neugebauer et al., VASP can correct for the leading errors (in many details, we have taken a more general approach, though).

Summary of relevant INCAR tags

This section contains a summary of all the INCAR tags that are currently implemented for performing monopole, dipole and quadrupole corrections using VASP. Please see the relevant pages of the respective tags for more detailed information.

Dimensionality of the system	Does the system have net charge?	Does the system have a net dipole moment?	Relevant INCAR tags for monopole/dipole corrections	Do energies converge with cell dimension?
3D	No	No	None	Yes
3D	Yes	No	NELECT: to set the charge LMONO: monopole corrections, only implemented for cubic cells EPSILON: scales monopole correction by dielectric constant of the medium	If the correct EPSILON value is used, the energies and relative energies will not depend on cell size. For solids, see LCALCEPS and LEPSILON
2D	No	Yes	IDIPOL=1,2,3: direction in which to apply the dipole correction to the total energy LDIPOL: enable dipole correction to the potential and forces DIPOL: center of mass to compute the dipole moment	Energies do not depend on the vacuum used (if sufficient vacuum is available)
2D	Yes	No	NELECT: to set the charge	Absolute energies do not converge with cell dimension, but energy differences might be useful
2D	Yes	Yes	NELECT: to set the charge	Absolute energies do not converge with cell dimension, but energy differences might be useful
0D (isolated molecules)	Yes	Yes	NELECT: to set the charge LMONO: monopole corrections, only implemented for cubic cells and only corrects the energy LDIPOL: monopole corrections with corrections for the potentials	Energies do not depend on cell dimension (for large enough cells)
0D (isolated molecules)	Yes	No	NELECT: to set the charge LMONO: monopole corrections, only implemented for cubic cells and only corrects the energy LDIPOL: monopole corrections with corrections for the potentials	Energies do not depend on cell dimension (for large enough cells)
0D (isolated molecules)	No	Yes	LDIPOL: dipole corrections with corrections for the potentials included	Energies do not depend on cell dimension (for large enough cells)

Tip: If an external electrostatic field is desired for slab, or molecular calculations, see EFIELD

Current limitations

For the current implementation, there are several restrictions; please read carefully:

• Charged systems:

Quadrupole corrections are only correct for cubic supercells (this means that the calculated 1/L³ corrections are wrong for charged supercells if the supercell is non-cubic). In addition, we have found empirically that for charged systems with excess electrons (NELECT>NELECT_neutral) more reliable results can be obtained if the energy after correction of the linear error (1/L) is plotted against 1/L³ to extrapolate results manually for L→∞. This is due to the uncertainties in extracting the quadrupole moment of systems with excess electrons.

• Potential corrections are only possible for orthorhombic cells (at least the direction in which the potential is corrected must be orthogonal to the other two directions).

Related Tags and Sections

NELECT, EPSILON, DIPOL, IDIPOL, LDIPOL, LMONO, EFIELD

Examples that use this tag

References

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