绝热表象下非绝热分子动力学方法

Nonadiabatic molecular dynamics under adiabatic representation

基于SSH(Su-Schriffer-Heeger)哈密顿的非绝热分子动力学方法广泛应用于模拟有机共轭聚合物中光激发过程和极化子运动.目前,该方法中电子波函数的演化是在透热表象中进行的,本文对该方法进行扩展,让电子波函数的演化在绝热表象下进行,给出了详细的公式推导过程.分别利用新、旧方法模拟了一条共轭聚合物链中光激发动力学过程,两种方法得到的数值计算结果相符.新方法可以加深对非绝热分子动力学方法的理解,提供激发态弛豫过程中不同分子轨道之间非绝热耦合强度等重要信息.

In this paper,we develop a nonadiabatic molecular dynamics method based on Su-Schriffer-Heeger(SSH)Hamiltonian,and this method is widely used to study the photoexcitation dynamics and polaron motion in conjugated polymers.However,in this method,the time-dependent Schrödinger equation has so far been solved in a diabatic representation,also known as site representation.In order to provide a deeper insight into the nonadiabatic molecular dynamics method,we solve the time-dependent Schrödinger equation in an adiabatic representation.The new method can directly provide the important information about the strength of nonadiabatic couplings between different molecular orbitals in the excited-state relaxation process,helping us to predict the electron and energy transfer within or between polymer chains.Solving the time-dependent Schrödinger equation in an adiabatic representation is much more complicated,it is mainly because we need to calculate the nonadiabatic couplings between different molecular orbitals.In this paper,the detailed formula derivation and actual calculation process of the nonadiabatic molecular dynamics method in an adiabatic representation are given.Using this new method,we simulate three photoexcitation processes in a conjugated polymer chain,HOMO→LUMO,HOMO–1→LUMO+1 and HOMO–2→LUMO+2.We analyze in detail the time evolutions of lattice configuration for these three photoexcitation processes,and compare these results with those obtained by diabatic representation(site representation)showing that the results obtained from these two representations are consistent with each other.