Electric field gradients from shifted-nucleus calculations:An alternative to the point charge nuclear quadrupole moment model

摘要

Combining the experimental nuclear quadrupole splittings with accurately calculated electric field gradients,q_(alphabeta)(N),at the nuclei (N) is known to be one of the most reliable sources of the nuclear quadrupole moments.This makes the development of methods for computing q_(alpha beta)(N) of particular interest.Formally,this first-order property is defined in terms of the expectation value of the field gradient operator q_(alphabeta)(N).However,for wave functions and methods which do not satisfy the Hellmann-Feynman theorem the correct definition of q_(alpha beta)(N) requires explicit energy differentiation with respect to some parameter-say,X-which defines the strength of the perturbation,gammaq_(alpha beta)(N).At this point one can choose between the gradient-type fully analytic differentiation of energies and purely numerical evaluation of their first-order derivatives with respect to X.