Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56126 Pisa, Italy.
Faraday Discuss. 2013;163:223-42; discussion 243-75. doi: 10.1039/c3fd20147c.
We present mixed quantum-classical simulation of the internal conversion between the lowest energy pipi* (S(La)) and npi* (S(n)) excited electronic states in adenine in the gas phase, adopting a quadratic vibronic model (QVC), parametrized with the help of PBE0 density functional calculations. Our approach is based on a hierarchical representation of the QVC Hamiltonian and a subsequent treatment of the most relevant coordinates at accurate time-dependent quantum level and of the other 'bath' modes at classical level. We predict an ultrafast transfer (-30 fs) of approximately 75% of the initial population excited on S(La) to S(n). Within an adiabatic picture, on the same timescale the wave packet concentrates almost completely on the lowest S1 state, where however it shows a very broad distribution with different characteristics (due to the different 'diabatic' character). It is shown that the proposed methodology offers a practicable route to describe the quantum dynamics of internal conversion processes in large semi-rigid systems.
我们提出了气相中腺嘌呤中最低能量 pipi*（S(La)）和 npi*（S(n)）激发电子态之间的内转换的混合量子经典模拟，采用了二次振子模型（QVC），并在 PBE0 密度泛函计算的帮助下进行了参数化。我们的方法基于 QVC 哈密顿量的分层表示，以及随后在精确的含时量子水平上处理最相关的坐标，以及在经典水平上处理其他“浴”模式。我们预测初始激发在 S(La)上的大约 75%的初始种群将迅速转移（-30 fs）到 S(n)。在绝热图像中，在相同的时间尺度内，波包几乎完全集中在最低的 S1 态，但它显示出非常宽的分布，具有不同的特征（由于不同的“绝热”特征）。结果表明，所提出的方法为描述大半刚性体系中内转换过程的量子动力学提供了一种可行的途径。
