Temperature effects on the structural phase transitions of gallium phosphide

In this work, we study the structural phase transitions of gallium phosphide (GaP), witha combination of molecular dynamics simulations (MD) and ab initio calculations based on density functional theory (DFT) with vibrational corrections within the harmonic approximation, for pressures up to 50 GPa. We show that the transition sequence depends on temperature for both cases. For low temperatures, our MD simulations predict a transition sequence zinc blende -> beta-tin -> Immm -> NaCl, while DFT predicts the sequence zinc blende -> Sc16 -> beta-tin -> Immm. Our DFT calculations with vibrational corrections also indicate that, for high temperatures, the Sc16 phase gradually loses stability and other structures such as Cmcm, beta-tin and NaCl become more stable. The kinetic effects are also studied by dynamically changing the pressure in MD simulations up to 200 GPa. We show that, as we increase the pressure, a transition to the beta-tin structure should not occur at room temperature due a large energy barrier. For higher temperatures, we show that the first transition is zinc blende -> NaCl. The differences in the observed transition sequence at low and high temperatures indicate that the vibrational corrections included in the DFT calculations are fundamental to the description of the stability of higher pressure structures, as also observed on other semiconductors. Moreover, the good agreement between DFT and MD shows the suitability of the classical effective many-body interaction potential, used to describe the different high-pressure phases of GaP.