LEFG: Difference between revisions
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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: | 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> | :<math> | ||
|V_{zz}| > |V_{xx}| > |V_{yy}| | |V_{zz}| > |V_{xx}| > |V_{yy}|. | ||
</math> | </math> | ||
The asymmetry parameter η=(''V''<sub>yy</sub>-''V''<sub>xx</sub>)/''V''<sub>zz</sub>. | The asymmetry parameter is defined as 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 | For so-called "quadrupolar nuclei", ''i.e.'', nuclei with nuclear spin I>1/2, NMR experiments can | ||
access ''V''<sub>zz</sub> and η. | access ''V''<sub>zz</sub> and η. | ||
Revision as of 13:48, 8 April 2019
LEFG = .TRUE. | .FALSE.
Default: LEFG = .FALSE.
Description: The LEFG Computes the Electric Field Gradient 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 is defined as 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.
To convert the Vzz values into the Cq often encountered in NMR literature, one has to specify the nuclear quadrupole moment by means of the QUAD_EFG-tag.
Beware: for heavy nuclei inaccuracies are to be expected because of an incomplete treatement of relativistic effects.