EFG

QTENS

This key activates the computation of the Nuclear Electric Quadrupole Hyperfine interaction. It can be applied to open-shell and to closed-shell systems. QTENS gives you the Nuclear Electric Quadrupole Hyperfine interaction (Q-tensor) [97]. The latter is directly related to the Electric Field Gradient (EFG) . The Q-tensor elements (in MHz) equal the the electric field gradient tensor elements (in a.u.) times 234.9647 times the nuclear quadrupole moment (NQM in barn units, 1 barn = 10-28m² = 10-24cm²) and divided by 2I(2I-1), where I is the nuclear spin. The Nuclear Quadrupole Coupling Constant (NQCC) (in MHz) is the largest value of the principal values of the EFG (in a.u.) times 234.9647 times the nuclear quadrupole moment (in barn units). The electric field gradient tensor is printed next to the Q-tensor.

In the case of ZORA the program will also calculate the EFG in the so called ZORA-4 approximation, which includes a small component density ("picture-change correction"), see [97]. If one includes spin-orbit coupling the EFG in the ZORA-4 approximation is only calculated if the symmetry in the calculation is NOSYM.