Dynamic mechanisms of the structural phase transitions in KNbO3: Moleculardynamics simulations

The question on the dominant driving mechanism (displacive or order-disorde r) 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 fer roelectric instabilities obtained by first-principles total energy calculat ions. The phase diagram as a function of temperature is obtained through co nstant-pressure molecular dynamics simulations. The analysis of the dynamic al structure factor and the microscopic dynamics of the particles in the di fferent phases allows us to reveal the nature of the dynamics associated wi th each structural transition. Correlations between local polarizations for ming chain-like precursor clusters in the paraelectric phase are examined.