Toward realistic dynamical simulations of advanced materials, including ultrafast phase transitions

We propose several new approaches to realistic dynamical simulations of advanced materials, including ultrafast phase transitions. The first three of these are illustrated with proof-of-principle calculations using simple models. In the first approach, correlation effects are included in a time-dependent quasiparticle equation which is based on the Kadanoff-Baym equations. This approach is appropriate for an ultrafast Mott-Hubbard transition. In the second approach, phenomenological Landau-Ginzburg-like order parameters are coupled to one another and to the vector potential of the laser pulse, so that the phase transition is described by time-dependent Landau-Ginzburg theory. This approach is appropriate for one mechanism which is apparently observed for light-induced superconductivity. In the third approach, an electronic temperature can be obtained in a density-functional simulation which omits electron correlation. In the fourth and most ambitious approach, a density-functional electronic Hamiltonian can be modified by the addition of pair-correlation-based terms which are determined self-consistently.