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Description: nuclear quadrupole moment (in millbarn) for the atomic types on the POTCAR file.

Setting the QUAD_EFG-tag allows the conversion of the Vzz (see LEFG) values into the Cq often encountered in NMR literature. The conversion formula is as follows (Q is the element and isotope specific quadrupole moment):

${\displaystyle C_{q}={\frac {eQV_{{zz}}}{h}}.}$

The QUAD_EFG-tag specifies the nuclear quadrupole moment in millibarns for each atomic species, in the same order as in the POTCAR file. The output Cq is in MHz. An online compilation of nuclear quadrupole moments can be found here or in Ref.[1].

Suppose a solid contains Al, C and Si, than the QUAD_EFG-tag could read:

QUAD_EFG = 146.6 33.27 0


27Al is the stable isotope of Al with a natural abundance of 100% and Q=146.6. The stable isotopes 12C and 13C are not quadrupolar nuclei, however, the radioactive 11C is. It has Q=33.27. For Si it is pointless to calculate a Cq: again all stable isotopes have I≤1/2. No moments are known for the other isotopes.

Beware: several definitions of ${\displaystyle C_{q}}$ are used in the NMR community.

Beware: for heavy nuclei inaccuracies are to be expected because of an incomplete treatement of relativistic effects.