Finite Electron Temperature Density Functional Theory and Neural Network Molecular Dynamics study of Sub Pico-Second Optical Control of Ferroelectric Domains in PbTiO₃ based Nanostructuress

Two temperature molecular dynamics based on finite electron temperature density functional theory (FT-DFT) has been successful in modeling optical excitation in materials as repopulation of the Fermi-Dirac distribution due to strong electron-field interactions. We employ FT-DFT based molecular dynamics to study the ferroelectric perovskite PbTiO₃ and find photo-induced charge transfer activation of optical phonons leads to a sub picosecond tetragonal/ferroelectric to cubic/paraelectric structural phase transition at 300K in the bulk structure. To study large polar domains common in PbTiO₃ based nanostructures we developed a neural-network force-field model based on ground state DFT and FT-DFT training data. Applications of the model to study polar vortex formation, domain wall structure, and their interactions in PbTiO₃ based nanostructures will be discussed.