Comparison of empirical bond-valence and first-principles energy calculations for a complex structural instability -: art. no. 174108

A simple bond-strain parameter, the so-called global-instability index, defined within the bond-valence model reproduces with striking accuracy the basic features of the ab initio total-energy surface around the energy minimum of SrBi2Ta2O9, but only for the degrees of freedom within the subspace of energetically unstable modes. These results imply that ab initio total-energy calculations and bond-valence criteria could be combined in the study and prediction of structural instabilities. The quantitative agreement between total-energy and bond-valence maps might be related to the irrelevance of cation-cation and anion-anion interactions within this subspace.