Temperature-dependent field gradients in Zn and Cd: First-principles analysis of electronic and lattice contributions

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Abstract
An ab initio investigation has been carried out for the influence of isotropic, anisotropic, and anharmonic phonons on the ionic and electronic contributions to the field gradients in zinc and cadmium. In addition to explaining the trend of experimental temperature-dependence data in these metals, it is shown that the different phonons influence the ionic and electronic contributions very differently. In particular, it is found that the isotropic components of the phonon spectra lead to no variation in the lattice contribution to the field gradient but produce substantial changes in the electronic contribution. These latter changes represent the leading contribution to the temperature dependence of the total field gradient. The net lattice contribution, composed of opposing contributions from the anisotropic and anharmonic components of phonon spectra is of the same order and sign as the electronic contribution, although somewhat smaller in magnitude. The relationship of our results to those from earlier work is discussed.