Lattice dynamics and hyperfine interactions inZnF2single crystals

Computation of Mössbauer isomer shifts from first principles

“…Computational quantum mechanics provides many schemes for computing the electron density and electric field gradient, including wavefunction-based methods in real space and reciprocal space, and density functional methods also in real space and reciprocal space [3][4][5][6][7][8][9][10][11][12]. One highly accurate method involves computing the wavefunctions of a molecule or cluster model of a solid using all-electron real-space methods [4,8,9].…”

“…Computational quantum mechanics provides many schemes for computing the electron density and electric field gradient, including wavefunction-based methods in real space and reciprocal space, and density functional methods also in real space and reciprocal space [3][4][5][6][7][8][9][10][11][12]. One highly accurate method involves computing the wavefunctions of a molecule or cluster model of a solid using all-electron real-space methods [4,8,9]. In this method as applied to solids, however, it is necessary to find ways of truncating the solid accurately, and it is also difficult to consider perturbations due to mechanical and electromagnetic fields, and to long-range magnetic ordering.…”

“…In this method as applied to solids, however, it is necessary to find ways of truncating the solid accurately, and it is also difficult to consider perturbations due to mechanical and electromagnetic fields, and to long-range magnetic ordering. For solid compounds treated with periodic boundary conditions, the most accurate method is the full-potential linearized augmented plane wave (LAPW) treatment [8][9][10]12], which is again an all-electron method. This is a highly accurate method but it is also computationally expensive, and so it is of interest to investigate whether it is possible using a pseudopotential or related method to achieve comparable accuracy in solids with periodic boundary conditions at lower computational cost.…”

Negative thermal expansion in ZnF$_2$

“…However even this non-magnetic solid showed anomalies in elastic constants at low temperatures not expected for ZnF 2 with no temperatureinduced phase transition. The observed softening of C 44 and C s = (C 11 − C 12 )/2 at low temperature in ZnF 2 had been interpreted as an incipient ferroelectric transition 9,10 but has also been contested 11,12 .…”

“…The lower panel of Fig. 4 shows the experimental and calculated volume thermal expansion coefficients α V in the low temperature range given by In order to check whether there exists any indication of incipient ferroelectric phase transition [9][10][11][12] in ZnF 2 at low temperature we refined the neutron powder diffraction data by the Rietveld method and determined the positional parameter x and the two Zn-F bond distances d 1 and d 2 as a function of temperature. Fig.…”