LEFG: Difference between revisions
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Description: compute the electric field gradients at positions of the atomic nuclei. | Description: compute the electric field gradients at positions of the atomic nuclei. | ||
---- | ---- | ||
For {{TAG|LEFG}}=.TRUE., the electric field | For {{TAG|LEFG}}=.TRUE., the electric field gradient tensors at the positions of the atomic nuclei are calculated using the method of Petrilli ''et al.''<ref name="petrilli:prb:98"/> | ||
The EFG tensors are symmetric. The principal components ''V''<sub>ii</sub> and asymmetry parameter η are printed for each atom. Following convention the principal components ''V''<sub>ii</sub> are ordered such that: | |||
:<math> | |||
|V_{zz}| > |V_{xx}| > |V_{yy}| | |||
</math> | |||
The asymmetry parameter η=(''V''<sub>yy</sub>-''V''<sub>xx</sub>)/''V''<sub>zz</sub>. | |||
For so-called "quadrupolar nuclei", ''i.e.'', nuclei with nuclear spin I>1/2, NMR experiments can | |||
access ''V''<sub>zz</sub> and η. | |||
'''Beware''': Attaining convergence can require somewhat smaller {{TAG|EDIFF}} than the default of <tt>1.e-4</tt> | |||
and somewhat larger cutoff {{TAG|ENCUT}} than default with {{TAG|PREC}}=A. Moreover, the calculation of | |||
EFGs typically requires high quality PAW data sets. Semi-core electrons can be important (check with | |||
<tt>*_pv</tt> or <tt>*_sv</tt> POTCARs) as well as explicit inclusion of augmentation channel(s) with ''d''-projectors. | |||
== Related Tags and Sections == | == Related Tags and Sections == | ||
Revision as of 00:43, 4 December 2012
LEFG = .TRUE. | .FALSE.
Default: LEFG = .FALSE.
Description: compute the electric field gradients at positions of the atomic nuclei.
For LEFG=.TRUE., the electric field gradient tensors at the positions of the atomic nuclei are calculated using the method of Petrilli et al.[1]
The EFG tensors are symmetric. The principal components Vii and asymmetry parameter η are printed for each atom. Following convention the principal components Vii are ordered such that:
The asymmetry parameter η=(Vyy-Vxx)/Vzz. For so-called "quadrupolar nuclei", i.e., nuclei with nuclear spin I>1/2, NMR experiments can access Vzz and η.
Beware: Attaining convergence can require somewhat smaller EDIFF than the default of 1.e-4 and somewhat larger cutoff ENCUT than default with PREC=A. Moreover, the calculation of EFGs typically requires high quality PAW data sets. Semi-core electrons can be important (check with *_pv or *_sv POTCARs) as well as explicit inclusion of augmentation channel(s) with d-projectors.