Makhov Dmitry V, Glover William J, Martinez Todd J, Shalashilin Dmitrii V
Department of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom.
Department of Chemistry and The PULSE Institute, Stanford University, Stanford, California 94305, USA and SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
J Chem Phys. 2014 Aug 7;141(5):054110. doi: 10.1063/1.4891530.
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.
我们提出了一种用于从头算量子非绝热分子动力学的新算法，该算法结合了从头算多重生成（AIMS）方法和多组态埃伦费斯特（MCE）方法的最佳特性。在这种新方法——从头算多重克隆（AIMC）中，各个轨迹基函数（TBFs）遵循埃伦费斯特运动方程（如在MCE中）。然而，当这些TBFs充分混合时，基组会扩展（如在AIMS中），以防止在平均势能面上进行长时间演化。我们将基组的扩展称为“克隆”，这类似于AIMS中的“生成”过程。AIMS和MCE的这种综合使我们能够在强非绝热耦合期间利用平均场演化的优势，同时避免埃伦费斯特动力学中的平均场伪影。我们探索使用时间位移基组“序列”作为一种低成本扩展基组的方法。我们还引入了一种新的括号平均泰勒展开（BAT）来近似所需的势能和非绝热耦合矩阵元。BAT近似避免了在TBFs之间的中间点计算电子结构信息的必要性，这是AIMS中通常使用的鞍点近似中所做的。AIMC的效率在乙烯第一激发态的非辐射衰变中得到了证明。AIMC方法已在AIMS-MOLPRO软件包中实现，该软件包已扩展以包含埃伦费斯特基函数。
