Ab initio study of photo-induced phase transitions

Ultrafast real-time lattice dynamics is a powerful tool to study the fundamental properties and behavior of solids. Ultrafast electronic dynamics in solids lies at the core of modern condensed matter and materials physics. To construct a practical ab initio method for studying solids under photoexcitation, we developed a momentum-resolved real-time time-dependent density functional theory algorithm using a numerical atomic basis, together with the implementation of both length and vector gauges of an electromagnetic field. When applied to the simulation of elementary excitations in both bulk and two-dimensional materials, different excitation modes are only distinguishable in momentum space. We also discuss various examples of photoinduced phase transitions such as amorphizations, charge density wave enhancements, and ultrafast solid-solid transitions.