Ab initio quantum direct dynamics simulations of ultrafast photochemistry with Multiconfigurational Ehrenfest approach

Abstract

The Multiconfigurational Ehrenfest (MCE) method is a quantum dynamics technique which allowstreatment of a large number of quantum nuclear degrees of freedom. This paper presents a reviewof MCE and its recent applications, providing a summary of the formalisms, including its ab initiodirect dynamics versions and also giving a summary of recent results. Firstly, we describe theMulticonfigurational Ehrenfest version 2 (MCEv2) method and its applicability to direct dynamicsand report new calculations which show that the approach converges to the exact result in modelsystems with tens of degrees of freedom. Secondly, we review previous ?on the fly? ab initioMultiple Cloning (AIMC-MCE) MCE dynamics results obtained for systems of a similar size, in whichthe calculations treat every electron and every nucleus of a polyatomic molecule on a fully quantumbasis. We also review the Time Dependent Diabatic Basis (TDDB) version of the technique and givean example of its application. We summarise the details of the sampling techniques andinterpolations used for calculation of the matrix elements, which make our approach efficient. Future directions of work are outlined.