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arXiv 2006.03149physics.chem-ph
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模拟非绝热电子-核动力学的混合量子-经典方法:细致平衡和改进的表面跳跃方法

Mixed quantum-classical approach to model non-adiabatic electron-nuclear dynamics: Detailed balance and improved surface hopping method

Eugene Stolyarov, Alexander White, Dmitry Mozyrsky

摘要:

我们发展了一个密度矩阵形式来描述耦合的电子-核动力学。为此,我们引入一个有效的哈密顿形式主义,描述电子跃迁和小(量子)核波动沿经典的核轨迹。利用这个哈密顿量,我们推导出运动方程的电子占领数和核坐标和动量。我们表明,在极限情况下,当耦合到给定电子跃迁的核自由度足够高时(即,强退相干极限),电子占据数的运动方程变为马尔可夫方程。此外,这些(速率)方程中的跃迁速率相对于较低能量到较高能量的跃迁是不对称的,反之亦然。在热平衡中,这种不对称对应于细致平衡条件。我们还研究了非马尔可夫区域的电子占据方程,并基于我们的形式发展了一个表面跳跃算法。为了处理退相干效应,我们引入额外的“虚拟”核波包,其与“真实”(物理)波包的干扰导致电子状态之间的耦合减少(即,退相干)以及相移,这提高了数值方法的精度。值得注意的是,相同的相移导致强退相干极限中的细致平衡条件。

英文摘要:

We develop a density matrix formalism to describe coupled electron-nuclear dynamics. To this end we introduce an effective Hamiltonian formalism that describes electronic transitions and small (quantum) nuclear fluctuations along a classical trajectory of the nuclei. Using this Hamiltonian we derive equations of motion for the electronic occupation numbers and for the nuclear coordinates and momenta. We show that in the limit when the number of nuclear degrees of freedom coupled to a given electronic transition is sufficiently high (i.e., the strong decoherence limit), the equations of motion for the electronic occupation numbers become Markovian. Furthermore the transition rates in these (rate) equations are asymmetric with respect to the lower-to-higher energy transitions and vice versa. In thermal equilibrium such asymmetry corresponds to the detailed balance condition. We also study the equations for the electronic occupations in non-Markovian regime and develop a surface hopping algorithm based on our formalism. To treat the decoherence effects we introduce additional "virtual" nuclear wavepackets whose interference with the "real" (physical) wavepackets leads to the reduction in coupling between the electronic states (i.e., decoherence) as well as to the phase shifts that improve the accuracy of the numerical approach. Remarkably, the same phase shifts lead to the detailed balance condition in the strong decoherence limit.

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