We have carried out molecular-dynamics simulations on BaX${\mathrm{F}}_4$ compounds, where X is Mg, Mn, or Zn. Ab initio potentials, with no adjustable parameters, were used to obtain short-range interactions between ion pairs. We found a polar ground-state structure which is in agreement with the A$2_1$am space group reported experimentally. We were able to reverse polarization in ${\mathrm{BaMgF}}_4$ at high temperatures, using large fields, but were unable to reverse polarization in the other compounds. The second-order phase transition in the Mn compound at 250 K was reproduced. We believe this to be the first extension of molecular dynamics to materials consisting of chains of F octahedra.

• Received 21 September 1993

DOI:https://doi.org/10.1103/PhysRevB.49.5811