Shell model potential for PbTiO3 and its applicability to surfaces and domain walls

We have developed an efficient interatomic potential for PbTiO3 in the framework of the shell model by fitting its parameters to reproduce both the mechanical and ferroelectric properties derived from ab initio density functional theory calculations. The optimized potential successfully yields the crystal structures, elastic properties and phonon dispersion curves, whereas the spontaneous polarization and effective charges are slightly underestimated. It reproduces well characteristic ferroelectric (FE) and antiferrodistortive (AFD) instabilities closely associated with the structural phase transition in PbTiO3, and is reliable under high tension and compression along the [ 001] direction. Furthermore, the potential is effective enough to describe 180 degrees and 90 degrees domain walls as well as the PbO-terminated surface with c(2 x 2) reconstruction where the FE and AFD distortions coexist. This significant success widely extends the applicable range of atomic-level simulations of ferroelectrics based on the shell model potential.