  First-principles molecular dynamics (FPMD) simulations were applied for the
paraelectric-ferroelectric phase transition in the perovskite-type cadmium
titanate, CdTiO3. Since the phase transition is reported to occur at the low
temperature around 80 K, the quantum thermal bath (QTB) method was utilized in
this study, which incorporates the nuclear quantum effects (NQEs). The
structural evolutions in the QTB-FPMD simulations are in reasonable agreement
with the experimental results, by contrast in the conventional FPMD simulations
using the classical thermal bath (CTB-FPMD). According to our phonon
calculations, volume expansion is the key in the stabilization of the
ferroelectric phase at low temperatures, which was well reproduced in the
QTB-FPMD with the NQEs. Thus, the NQEs are of importance in phase transitions
at low temperatures, particularly below the room temperature, and the QTB is
useful in that it incorporates the NQEs in MD simulations with low
computational costs comparable to the conventional CTB.
