University of Chemistry and Technology Prague, Department of Physical Chemistry, Technická 5, 16628 Prague 6, Czech Republic.
Phys Chem Chem Phys. 2020 May 21;22(19):10550-10560. doi: 10.1039/c9cp06154a. Epub 2020 Feb 3.
We discuss a fragment-based QM:QM scheme as a practical way to access the energetics of vertical electronic processes in the condensed phase. In the QM:QM scheme, we decompose the large molecular system into small fragments, which interact solely electrostatically. The energies of the fragments are calculated in a self-consistent field generated by the other fragments and the total energy of the system is calculated as a sum of the fragment energies. We show on two test cases (cytosine and a sodium cation) that the method allows one to accurately simulate the shift of vertical ionization energies (VIE) while going from the gas phase to the bulk. For both examples, the predicted solvent shifts and peak widths estimated at the DFT level agree well with the experimental observations. We argue that the QM:QM approach is more suitable than either an electrostatic embedding based QM/MM approach, a full quantum description at the DFT level with a generally used functional or a combination of both. We also discuss the potential scope of the applicability for other electronic processes such as Auger decay.
我们讨论了一种基于片段的量子力学/量子力学(QM:QM)方案，作为一种实用的方法来获取凝聚相垂直电子过程的能量。在 QM:QM 方案中，我们将大的分子系统分解成仅静电相互作用的小片段。通过其他片段产生的自洽场来计算片段的能量，系统的总能量是各片段能量的总和。我们通过两个测试案例（胞嘧啶和钠离子）表明，该方法允许在从气相到体相的过程中准确模拟垂直电离能（VIE）的移动。对于这两个例子，在 DFT 水平上预测的溶剂位移和估计的峰宽与实验观察结果吻合良好。我们认为，QM:QM 方法比基于静电嵌入的 QM/MM 方法、使用一般功能的全量子描述的 DFT 水平或两者的组合更适用。我们还讨论了其他电子过程（如俄歇衰变）的潜在适用范围。
