Quantitative analysis of the first-principles effective Hamiltonian approach to ferroelectric perovskites

S. TINTE; J. IÑIGUEZ; KARIN M. RABE; DAVID VANDERBILT

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2003 vol. 67 p. 64106 - 64106

1098-0121

The various approximations used in the construction of a first-principles effective Hamiltonian for BaTiO3 ,and their effects on the calculated transition temperatures, are discussed. An effective Hamiltonian for BaTiO3is constructed not from first-principles calculations, but from the structural energetics of an atomistic shellmodel for BaTiO3 of Tinte et al. This allows the elimination of certain uncontrolled approximations that arisein the comparison of first-principles effective Hamiltonian results with experimental values and the quantifi-cation of errors associated with the selection of the effective Hamiltonian subspace and subsequent projection.The discrepancies in transition temperatures computed in classical simulations for this effective Hamiltonianand for the atomistic shell model are shown to be associated primarily with a poor description of the thermalexpansion in the former case. This leads to specific proposals for refinements to the first-principles effectiveHamiltonian method. Our results suggest that there are at least two significant sources of error in the effective-Hamiltonian treatment of BaTiO3 in the literature, i.e., the improper treatment of thermal expansion and theerrors inherent in the first-principles approach itself.