Constant pressure molecular dynamics simulation for ionic system

We present in this work a novel application of constant pressure molecular dynamics method (MD) that allows shape variation of MD cells. The new pressostat method, based on metric-tensor flexible-cell algorithm that has patched the drawbacks of the original P-R algorithm, is extended to address the long range charge-charge interaction in ionic systems by combining its usage with the Ewald summation method. It can reflect the underlying oscillation of the MD cells by releasing the constraint of fixed shape of the simulation box, which was not resolved successfully by other methods previously. We also show that when equipped with the Nose-Poincare thermostat algorithm, the new method can properly describe the evolution of the system in isothermal-isobaric (NPT) ensemble. The reliability of the new method is verified by the results from its application on solid NaCl at given temperatures and pressures. Other applications on the phase transition of ZrO₂ from tetragonal to cubic reveals that the effective axial ratio of (a + b)/2c changes from 0.922 to 1, showing a good match to that from experimental measurement. The new algorithm has potential applications to other ionic systems to obtain various material properties.