PRECFOCK: Difference between revisions

Revision as of 13:29, 15 February 2011

PRECFOCK = Low | Medium | Fast | Normal | Accurate
Default: PRECFOCK = Normal

Description: PRECFOCK controls the FFT grids used in the exact exchange routines (Hartree-Fock and hybrid functionals).

PRECFOCK	FFT-grid	Augmentation charge	Quality
Low	G_cut	identical to standard DFT	large noise in forces/energy errors
Medium	identical to std. FFT	identical to standard DFT	some noise in forces/good energy
Fast	G_cut	very soft augmentation charge^a	some noise in forces/good energy
Normal	3/2×G_cut	soft augmentation charge^b	accurate forces and energy
Accurate	2×G_cut	soft augmentation charge^b	very accurate forces and energy
^a radius for augmentation sphere is increased by factor 1.25 compared to default. ^b radius is increased by factor 1.35 compared to default except for s -like charge, for the s -channel the radius of the augmentation sphere is increased by a factor 1.25.

where

E_{\rm {cut}}={\frac {\hbar ^{2}}{2m_{e}}}G_{\rm {cut}}^{2}

with E_cut=ENCUT.

@@ Line 16: / Line 16: @@
 | Accurate || 2&times;G<sub>cut</sub> || soft augmentation charge<sup>b</sup> || very accurate forces and energy
 |-
-|colspan="4"|<sup>a</sup > soft augmentation charge: radius for augmentation sphere is increased by factor 1.25 compared to default.
+|colspan="4"|<sup>a</sup > radius for augmentation sphere is increased by factor 1.25 compared to default.
-<sup>b</sup> very soft augmentation charge: radius is increased by factor 1.35 compared to default except for ''s''-like charge, for the ''s''-channel the radius of the augmentation sphere is increased by a factor 1.25.
+<sup>b</sup> radius is increased by factor 1.35 compared to default except for ''s'' -like charge, for the ''s'' -channel the radius of the augmentation sphere is increased by a factor 1.25.
 |}