Dynamic mechanisms of the structural phase transitions in KNbO3:: Molecular dynamics simulations

The question on the dominant driving mechanism (displacive or order-disorder) at each structural phase transition of KNbO3 is investigated by means of molecular dynamics simulations. To this purpose, we first develop a shell model by determining its potential parameters in order to reproduce the ferroelectric instabilities obtained by first-principles total energy calculations. The phase diagram as a function of temperature is obtained through constant-pressure molecular dynamics simulations. The analysis of the dynamical structure factor and the microscopic dynamics of the particles in the different phases allows us to reveal the nature of the dynamics associated with each structural transition. Correlations between local polarizations forming chain-like precursor clusters in the paraelectric phase are examined.