Ab initio Studies of the Phase Transitions in K2SeO4.

摘要

An ab initio model is developed for the potentials in ionic molecular solids in which the electron covalenc within the molecular ions substantially affects the interionic interactions. By treating the intermolecular and intramolecular interactions on the basis of the true electrons charge densities of the molecular ions, this new model leads to an accurate parameter-free description of the potential-energy surfaces for such crystals. We performed first-principles static structural relaxation, super-cell molecular-dynamics simulation, and lattice-dynamics studies for the room-temperature paraelectric phase and the lower-temperature ferroelectric superstructure of K2SeO4 and predicted with good accuracy the transition from the former to the latter.