Theory of the transferred hyperfine interaction between well-separated atoms and the influence of soft-phonon modes.

Abstract

We have calculated the transferred hyperfine interaction at the ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ ion in ${\mathrm{PbF}}_{2}$ in which the distance between ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ and ${\mathrm{Pb}}^{2+}$ is 30% larger than the bond lengths in ${\mathrm{MnF}}_{2}$. The contributions arising from the overlap of wave functions and the charge transfer and the charge redistribution effects have been calculated from first principles and the s, ${p}_{\ensuremath{\sigma}}$, and ${p}_{\ensuremath{\pi}}$ spin densities have been found. The change in the transferred hyperfine coupling due to a soft-phonon mode which goes to zero at a temperature of ${T}_{c}$=50 K has been calculated and verified experimentally.