Order-disorder, local structure and precursor effects in BaTiO3

Interatomic potentials are determined in the framework of the nonlinear oxy gen polarizability model to describe the structural behavior of BaTiO3. To this purpose, the adiabatic potential is evaluated for different ferroelect ric distortions and the model potential parameters are obtained by comparin g with LAPW total energy calculations. The phase diagram as a function of t emperature is obtained through constant pressure molecular dynamics simulat ions, and the non-trivial phase sequence is correctly reproduced. Calculati ons of the pair distribution function indicate that order-disorder is the d ominant dynamics at all transitions. Precursor clusters with local polariza tions correlated along Ti-O chains are determined to persist several hundre ds of degrees above the para-ferroelectric transition.