Fedorov Dmitry A, Pruitt Spencer R, Keipert Kristopher, Gordon Mark S, Varganov Sergey A
Department of Chemistry, University of Nevada, Reno , 1664 North Virginia Street, Reno, Nevada 89557-0216, United States.
Argonne Leadership Computing Facility, Argonne National Laboratory , 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
J Phys Chem A. 2016 May 12;120(18):2911-9. doi: 10.1021/acs.jpca.6b01406. Epub 2016 Apr 27.
Dynamics at intersystem crossings are fundamental to many processes in chemistry, physics, and biology. The ab initio multiple spawning (AIMS) method was originally developed to describe internal conversion dynamics at conical intersections where derivative coupling is responsible for nonadiabatic transitions between electronic states with the same spin multiplicity. Here, the applicability of the AIMS method is extended to intersystem crossing dynamics in which transitions between electronic states with different spin multiplicities are mediated by relativistic spin-orbit coupling. In the direct AIMS dynamics, the nuclear wave function is expanded in the basis of frozen multidimensional Gaussians propagating on the coupled electronic potential energy surfaces calculated on the fly. The AIMS method for intersystem crossing is used to describe the nonadiabatic transitions between the (3)B1 and (1)A1 states of GeH2. The potential energies and gradients were obtained at the CASSCF(6,6)/6-31G(d) level of theory. The spin-orbit coupling matrix elements were calculated with the configuration interaction method using the two-electron Breit-Pauli Hamiltonian. The excited (3)B1 state lifetime and intersystem crossing rate constants were estimated by fitting the AIMS state population with the first-order kinetics equation for a reversible unimolecular reaction. The obtained rate constants are compared with the values predicted by the statistical nonadiabatic transition state theory with transition probabilities calculated using the Landau-Zener and weak coupling formulas.
系间窜越动力学对于化学、物理和生物学中的许多过程至关重要。从头算多重产生（AIMS）方法最初是为描述锥形交叉点处的内转换动力学而开发的，在锥形交叉点处，导数耦合负责具有相同自旋多重性的电子态之间的非绝热跃迁。在此，AIMS方法的适用性扩展到系间窜越动力学，其中具有不同自旋多重性的电子态之间的跃迁由相对论自旋 - 轨道耦合介导。在直接AIMS动力学中，核波函数在动态计算的耦合电子势能面上传播的冻结多维高斯函数的基础上展开。用于系间窜越的AIMS方法用于描述GeH2的（3）B1和（1）A1态之间的非绝热跃迁。势能和梯度在CASSCF(6,6)/6 - 31G(d)理论水平上获得。自旋 - 轨道耦合矩阵元使用双电子Breit - Pauli哈密顿量通过组态相互作用方法计算。通过将AIMS态布居与可逆单分子反应的一级动力学方程拟合，估计了激发的（3）B1态寿命和系间窜越速率常数。将获得的速率常数与统计非绝热过渡态理论预测的值进行比较，其中过渡概率使用Landau - Zener和弱耦合公式计算。
