ENCUT: Difference between revisions

Revision as of 09:08, 17 October 2023

ENCUT = [real]

Default: ENCUT

= largest ENMAX in the POTCAR file

Description: ENCUT specifies the energy cutoff for the plane-wave basis set in eV.

All plane waves with a kinetic energy smaller than $E_{\mathrm {cut} }$ are included in the basis set, i.e.,

|\mathbf {G} +\mathbf {k} |<G_{\mathrm {cut} }

with

E_{\mathrm {cut} }={\frac {\hbar ^{2}}{2m}}G_{\mathrm {cut} }^{2}

With such a energy cutoff, the number of plane waves is not the same for all k-points, leading to a superior behavior for energy-volume calculations, for instance. The total number of plane waves changes fairly smoothly according to the volume. The criterion $|\mathbf {G} |<G_{\mathrm {cut} }$ (i.e. same basis set for each k-point) would lead to a very rough energy-volume curve and, generally, slower energy convergence.

The POTCAR files contain a default ENMAX (and ENMIN), therefore it is in principle not necessary to specify ENCUT in the INCAR file. For calculations with more than one species, the maximum cutoff ENMAX or ENMIN value is used for the calculation (see PREC).

Important: We strongly recommend specifying the energy cutoff ENCUT always manually in the INCAR file to ensure the same accuracy between calculations. Otherwise, the default ENCUT may differ among the different calculations (e.g., for the calculation of the cohesive energy), with the consequence that the total energies, for instance, can not be compared.

@@ Line 9: / Line 9: @@
 ::<math> | \mathbf{G} + \mathbf{k} | < G_{\mathrm{cut}} </math> with <math> E_{\mathrm{cut}} = \frac{\hbar^2}{2m} G^2_{\mathrm{cut}} </math>
-The number of plane waves differs for each '''k'''-point, leading to a superior behavior for, e.g. energy-volume calculations.
+With such a energy cutoff, the number of plane waves is not the same for all '''k'''-points, leading to a superior behavior for energy-volume calculations, for instance.
-If the volume is increased the total number of plane waves changes fairly smoothly.
+The total number of plane waves changes fairly smoothly according to the volume.
-The criterion <math>| \mathbf{G} | <   G_{\mathrm{cut}} </math> (i.e. same basis set for each '''k'''-point) would lead to a very rough energy-volume curve and, generally, slower energy convergence.
+The criterion <math>| \mathbf{G} | <  G_{\mathrm{cut}} </math> (i.e. same basis set for each '''k'''-point) would lead to a very rough energy-volume curve and, generally, slower energy convergence.
 The {{FILE|POTCAR}} files contain a default {{TAG|ENMAX}} (and {{TAG|ENMIN}}), therefore it is in principle not necessary to specify {{TAG|ENCUT}} in the {{FILE|INCAR}} file.

Revision as of 09:08, 17 October 2023

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