Röhrig Ute F, Frank Irmgard, Hutter Jürg, Laio Alessandro, VandeVondele Joost, Rothlisberger Ursula
Laboratory of Inorganic Chemistry, Swiss Federal Institute of Technology, 8093 Zurich, Switzerland.
Chemphyschem. 2003 Nov 14;4(11):1177-82. doi: 10.1002/cphc.200300650.
We present a hybrid Car-Parrinello quantum mechanical/molecular mechanical (QM/MM) approach that is capable of treating the dynamics of molecular systems in electronically excited states in complex environments. The potential energy surface in the excited state is described either within the restricted open-shell Kohn-Sham (ROKS) formalism or within time-dependent density functional theory (TDDFT). As a test case, we apply this technique to the study of the solvent effects on the ground state and on the first excited singlet state of acetone in water. Our results demonstrate that for this system a purely classical description of the solvent is sufficient, since inclusion of the first solvent shell of 12 water molecules into the quantum system does not show a significant effect on this transition. The excited-state energies calculated with ROKS are red shifted by a constant value compared to the TDDFT results, while the relative variations of the excitation energy for different configurations are in very good agreement. The experimentally observed blue shift of the excitation energy in going from gas phase to condensed phase is well reproduced. Excited-state dynamics carried out with ROKS yield the relaxation of the solute and the rearrangement of the solvent structure on a picosecond timescale. The calculated Stokes shift is in reasonable agreement with experimental data.
我们提出了一种混合的卡-帕里尼罗量子力学/分子力学（QM/MM）方法，该方法能够处理复杂环境中处于电子激发态的分子系统的动力学。激发态的势能面可以用受限开壳层科恩-沙姆（ROKS）形式理论或含时密度泛函理论（TDDFT）来描述。作为一个测试案例，我们将这项技术应用于研究溶剂对水中丙酮基态和第一激发单重态的影响。我们的结果表明，对于这个系统，对溶剂进行纯粹的经典描述就足够了，因为将包含12个水分子的第一溶剂壳层纳入量子系统对这种跃迁并没有显著影响。与TDDFT结果相比，用ROKS计算的激发态能量会有一个恒定值的红移，而不同构型的激发能的相对变化则非常吻合。从气相到凝聚相时实验观察到的激发能蓝移得到了很好的重现。用ROKS进行的激发态动力学研究得出溶质在皮秒时间尺度上的弛豫以及溶剂结构的重排。计算得到的斯托克斯位移与实验数据合理吻合。
