Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, USA.
J Chem Phys. 2018 Oct 28;149(16):164109. doi: 10.1063/1.5048627.
We report an extension of a hybrid polarizable embedding method incorporating solvent effects in the calculations of two-photon absorption (2PA) cross sections. We employ the equation-of-motion coupled-cluster singles and doubles method for excitation energies (EOM-EE-CCSD) for the quantum region and the effective fragment potential (EFP) method for the classical region. We also introduce a rigorous metric based on 2PA transition densities for assessing the domain of applicability of QM/MM (quantum mechanics/molecular mechanics) schemes for calculating 2PA cross sections. We investigate the impact of the environment on the 2PA cross sections of low-lying transitions in microhydrated clusters of -nitroaniline, thymine, and the deprotonated anionic chromophore of photoactive yellow protein (PYPb). We assess the performance of EOM-EE-CCSD/EFP by comparing the 2PA cross sections against full QM calculations as well as against the non-polarizable QM/MM electrostatic embedding approach. We demonstrate that the performance of QM/EFP improves when few explicit solvent molecules are included in the QM subsystem. We correlate the errors in the 2PA cross sections with the errors in the key electronic properties-identified by the analysis of 2PA natural transition orbitals and 2PA transition densities-such as excitation energies, transition moments, and dipole-moment differences between the initial and final states. Finally, using aqueous PYPb, we investigate the convergence of 2PA cross sections to bulk values.
我们报告了一种扩展的混合极化嵌入方法，该方法将溶剂效应纳入双光子吸收（2PA）截面的计算中。我们采用了用于激发能的运动方程耦合簇单双（EOM-EE-CCSD）方法，用于量子区域，采用有效片段势（EFP）方法用于经典区域。我们还引入了一种基于 2PA 跃迁密度的严格度量，用于评估用于计算 2PA 截面的QM/MM（量子力学/分子力学）方案的适用范围。我们研究了环境对硝基苯胺、胸腺嘧啶的低能跃迁微水合簇以及光活性黄蛋白（PYPb）的去质子阴离子发色团的 2PA 截面的影响。我们通过将 2PA 截面与全 QM 计算以及非极化 QM/MM 静电嵌入方法进行比较，评估了 EOM-EE-CCSD/EFP 的性能。我们证明，当在 QM 子系统中包含少量显式溶剂分子时，QM/EFP 的性能会提高。我们将 2PA 截面中的误差与关键电子性质中的误差相关联，这些性质通过 2PA 自然跃迁轨道和 2PA 跃迁密度的分析来确定，例如激发能、跃迁矩以及初始和最终状态之间的偶极矩差异。最后，我们使用水溶液 PYPb 研究了 2PA 截面向体相值的收敛性。
