Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui, China; Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong.
J Comput Chem. 2013 Oct 15;34(27):2380-8. doi: 10.1002/jcc.23401. Epub 2013 Aug 6.
Conventional combined quantum mechanical/molecular mechanical (QM/MM) methods lack explicit treatment of Pauli repulsions between the quantum-mechanical and molecular-mechanical subsystems. Instead, classical Lennard-Jones (LJ) potentials between QM and MM nuclei are used to model electronic Pauli repulsion and long-range London dispersion, despite the fact that the latter two are inherently of quantum nature. Use of the simple LJ potential in QM/MM methods can reproduce minimal geometries and energies of many molecular clusters reasonably well, as compared to full QM calculations. However, we show here that the LJ potential cannot correctly describe subtle details of the electron density of the QM subsystem because of the neglect of Pauli repulsions between the QM and MM subsystems. The inaccurate electron density subsequently affects the calculation of electronic and magnetic properties of the QM subsystem. To explicitly consider Pauli interactions with QM/MM methods, we propose a method to use empirical effective potentials on the MM atoms. The test case of the binding energy and magnetic properties of a water dimer shows promising results for the general application of effective potentials to mimic Pauli repulsions in QM/MM calculations.
传统的量子力学/分子力学（QM/MM）方法缺乏对量子力学和分子力学子系统之间的 Pauli 排斥的明确处理。相反，尽管后两者本质上是量子性质的，但在 QM 和 MM 原子核之间使用经典的 Lennard-Jones（LJ）势来模拟电子 Pauli 排斥和长程伦敦色散。在 QM/MM 方法中使用简单的 LJ 势可以很好地再现许多分子簇的最小几何形状和能量，与全 QM 计算相比。然而，我们在这里表明，由于忽略了 QM 和 MM 子系统之间的 Pauli 排斥，LJ 势不能正确描述 QM 子系统电子密度的微妙细节。随后不准确的电子密度会影响 QM 子系统电子和磁性性质的计算。为了明确地考虑与 QM/MM 方法的 Pauli 相互作用，我们提出了一种在 MM 原子上使用经验有效势的方法。水二聚体的结合能和磁性性质的测试案例表明，有效势在 QM/MM 计算中模拟 Pauli 排斥的一般应用具有有希望的结果。
