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Ultrafast Theory and Simulation

Understanding charge and energy flow in molecules and materials is a key to designing better means for converting light into chemical and/or electrical energy. The theory group in PULSE is focused on developing and applying new methods that can describe the behavior of molecules after they absorb light.

Realistic description of the ultrafast response of molecules to light absorption must account for the quantum mechanical nature of both the electrons and the nuclei. We have developed the ab initio multiple spawning (AIMS) method which solves the electronic and nuclear Schrödinger equations simultaneously in order to accomplish this goal. A schematic of the method is shown below. The nuclei are described by quantum mechanical wavepackets which move on potential energy surfaces that are determined “on the fly,” i.e. during the dynamical simulation. A key ingredient to the AIMS method is the “spawning” which is a way to adaptively increase the size of the basis set describing the nuclear wavefunction when quantum mechanical effects are expected to be large.