title: Ab initio multiple cloning algorithm for quantum nonadiabatic molecular dynamics.
abstract: We present a new algorithm for ab initio quantum nonadiabatic molecular dynamics that combines the best features of ab initio Multiple Spawning (AIMS) and Multiconfigurational Ehrenfest (MCE) methods. In this new method, ab initio multiple cloning (AIMC), the individual trajectory basis functions (TBFs) follow Ehrenfest equations of motion (as in MCE). However, the basis set is expanded (as in AIMS) when these TBFs become sufficiently mixed, preventing prolonged evolution on an averaged potential energy surface. We refer to the expansion of the basis set as "cloning," in analogy to the "spawning" procedure in AIMS. This synthesis of AIMS and MCE allows us to leverage the benefits of mean-field evolution during periods of strong nonadiabatic coupling while simultaneously avoiding mean-field artifacts in Ehrenfest dynamics. We explore the use of time-displaced basis sets, "trains," as a means of expanding the basis set for little cost. We also introduce a new bra-ket averaged Taylor expansion (BAT) to approximate the necessary potential energy and nonadiabatic coupling matrix elements. The BAT approximation avoids the necessity of computing electronic structure information at intermediate points between TBFs, as is usually done in saddle-point approximations used in AIMS. The efficiency of AIMC is demonstrated on the nonradiative decay of the first excited state of ethylene. The AIMC method has been implemented within the AIMS-MOLPRO package, which was extended to include Ehrenfest basis functions.
authors.affiliation: Department of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom.
authors.forename: Dmitry V
authors.initials: DV
authors.lastname: Makhov
authors.affiliation: Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Glover
authors.affiliation: Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Martinez
authors.affiliation: Department of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom.
authors.forename: Dmitrii V
authors.initials: DV
authors.lastname: Shalashilin
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004735:Energy Transfer; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D044367:Phase Transition; D011789:Quantum Theory; D012984:Software; D013816:Thermodynamics