An exact approach to compute physical properties for general multi-electronic-state (MES) systems in thermal equilibrium is presented.[1] The approach is extended from our recent progress on path integral molecular dynamics (PIMD) [2,3] for quantum statistical mechanics when a single potential energy surface is involved. We first define an effective potential function that is numerically favorable for MES-PIMD, and then derive corresponding estimators in MES-PIMD for evaluating various physical properties. Its application to several representative one-dimensional and multi-dimensional models [1,4] demonstrates that MES-PIMD in principle offers a practical tool in either of the diabatic and adiabatic representations for studying exact quantum statistics of complex/large MES systems when the Born-Oppenheimer approximation, Condon approximation, and harmonic bath approximation are invalid.

Exact approach for quantum statistics of multi-electronic-state systems

2019 Spring National Meeting

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