Principles of modeling the fluorescence spectral dynamics of dye molecules in solutions

FSDS is Fluorescence Spectral Dynamics Simulator, designed to investigate photoinduced charge transfer and its manifestations in time-resolved fluorescence spectra of a dye in a solvent. The project is implemented in C, using the MPI library. The computer model simulates stationary absorption and fluorescence spectra, as well as the time evolution of population distributions along the solvent reaction coordinate, to calculate spectral dynamics. Excitation and relaxation of intramolecular high-frequency vibrations are described at the quantum level. FSDS can fit the physical parameters of the dyes to experimental data. The dye excitation is consistently described accounting for the finite duration of the pump pulse. The program code implements two evolutionary models: a spin-boson model within the harmonic potential and a stochastic model based on the Smoluchowski diffusion operator for an arbitrary free energy surface. Computer simulation shows the numerical coincidence of the calculations performed in the framework of these models for the harmonic free energy surface. The detail description of the code and numerical schemes are presented.FSDS即荧光光谱动力学模拟器（Fluorescence Spectral Dynamics Simulator），旨在研究光诱导电荷转移及其在溶剂中染料的时间分辨荧光光谱中的表现形式。该项目以C语言编写，依托消息传递接口（Message Passing Interface，MPI）库开发。该计算机模型可模拟稳态吸收光谱与荧光光谱，并沿溶剂反应坐标模拟布居分布的时间演化，以此计算光谱动力学过程。分子内高频振动的激发与弛豫采用量子力学层面的描述方法。FSDS可将染料的物理参数与实验数据进行拟合。染料的激发过程可得到一致描述，同时计入泵浦脉冲的有限持续时长。该程序代码实现了两类演化模型：一是谐振势框架下的自旋-玻色子模型（spin-boson model），二是基于斯莫卢霍夫斯基扩散算子（Smoluchowski diffusion operator）、适用于任意自由能面的随机模型。计算机模拟结果表明，在谐振子自由能面的框架下，两类模型的计算结果具有数值一致性。本文详细介绍了该代码与数值方案。