ENCUT: Difference between revisions

Revision as of 09:25, 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^2_{\mathrm{cut}}

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

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>
-With such a energy cutoff, the number of plane waves is not the same for all '''k'''-points, leading to a superior behavior. For instance, for energy-volume calculations the total number of plane waves changes fairly smoothly according to the volume, while the criterion <math>| \mathbf{G} | < G_{\mathrm{cut}} </math> (i.e. same number of plane waves for all '''k'''-points) would lead to a very rough energy-volume curve and, generally, slower energy convergence with respect to the basis set size {{TAG|ENCUT}}.
+With such a energy cutoff, the number of plane waves included in the basis set is not the same for all '''k'''-points, leading to a superior behavior. For instance, for energy-volume calculations the total number of plane waves changes fairly smoothly according to the volume, while the criterion <math>| \mathbf{G} | < G_{\mathrm{cut}} </math> (i.e. same number of plane waves for all '''k'''-points) would lead to a very rough energy-volume curve and, generally, slower energy convergence with respect to the basis set size {{TAG|ENCUT}}.
 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 09:25, 17 October 2023

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