Lattice instabilities, anharmonicity and phase transitions in PbZrO3from first principles

An effective Hamiltonian for the antiferroelectric transition in PbZrO3 is constructed from first-principles density-functional-theory total-energy and linear-response calculations through the use of a localized, symmetrized basis set of “lattice Wannier functions''. The effective Hamiltonian consists of three-component vector degrees of freedom at the Pb sites and two-component vector degrees of freedom at the oxygen sites. This effective Hamiltonian allows us to analyze the structural energetics and identify the role of various physical contributions. We find that there exists a strong competition between sets of coupled unstable modes in producing low energy states. Two such groups of instabilities found from the effective Hamiltonian are seen to be relevant to the experimental ground and intermediate states.