Ultrafast Dynamics on Many Electronic States

Many important problems in chemistry and materials science involve nonadiabatic dynamics on large numbers of electronic states. Phenomena important for strong-field physics, energy conversion, hot carrier cooling, and relaxation of plasmonic excitations fall into this category. Some of these phenomena involve long lived coherences, which are challenging to accurately model with many mixed quantum-classical methods. We will present recent theoretical developments towards an accurate and broadly applicable simulation method for modeling dynamics in this regime. Specifically, we will present the development of the Ehrenfest with collapse to a block (TAB) method and a derivative designed for dense manifolds of states (DMS). The primary achievement of TAB-DMS is that it is able to accurately describe decoherence effects without requiring explicit computation of individual electronic eigenstates. Coupling to graphics processing unit accelerated time-dependent configuration interaction software to TAB and TAB-DMS enables ab initio nonadiabatic molecular dynamics simulations on many electronic states, in full nuclear dimensionality, and without prior knowledge of reaction mechanism. The utility of this approach will be demonstrated by application to long-lived electronic coherences observed in recent ultrafast experiments.