Full quantum effects in physics

Ions are commonly approximated to classical point-like particles in traditional ab initio studies. However, in certain systems, their quantum effects are crucial to the physical properties and physical processes. A full quantum calculation, which includes this quantum effect, shows unique advantages in such systems. Path Integral Molecular Dynamics (PIMD) has become the most widely used full quantum simulation method. Ab initio PIMD keeps the electron structure and ground state energy of ab initio calculations, while the ions move according to a set of equations which contain the nuclear quantum effect. Proton transfer in BaZrO3 has been studied by PIMD. The results show that the nuclear quantum effect has different influences on the two different subprocesses, reducing the barrier of the transfer process more significantly than the reorientation process, which makes the transfer process faster. This agrees with the experimental observations but differs from the results of early ab initio simulations without the full quantum effect, which indicate that the transfer process is rate-limiting.