First-principles model potentials for lattice-dynamical studies: general methodology and example of application to ferroic perovskite oxides.

摘要: We present a scheme to construct model potentials, with parameters computed from first principles, for large-scale lattice-dynamical simulations of materials. mimic the traditional solid-state approach investigation vibrational spectra, i.e., we start suitably chosen reference configuration compound and describe its energy as function arbitrary atomic distortions by means Taylor series. Such form potential-energy surface is general, trivial formulate any material, physically transparent. Further, such models involve clear-cut approximations, their precision can be improved in systematic fashion, simplicity allows convenient practical strategies compute/fit potential parameters. illustrate our two challenging cases which strongly anharmonic, namely, ferroic perovskite oxides PbTiO3 SrTiO3. Studying these compounds us better connection between so-called effective-Hamiltonian method ours (which may seen an extension former), show physical insight predictive power provided approach-e.g., new results regarding factors controlling phase-transition temperatures, novel phase transitions under elastic constraints, treatment thermal expansion, etc.