Hratchian Hrant P, Parandekar Priya V, Raghavachari Krishnan, Frisch Michael J, Vreven Thom
Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.
J Chem Phys. 2008 Jan 21;128(3):034107. doi: 10.1063/1.2814164.
An accurate first-principles treatment of chemical reactions for large systems remains a significant challenge facing electronic structure theory. Hybrid models, such as quantum mechanics:molecular mechanics (QM:MM) and quantum mechanics:quantum mechanics (QM:QM) schemes, provide a promising avenue for such studies. For many chemistries, including important reactions in materials science, molecular mechanics or semiempirical methods may not be appropriate, or parameters may not be available (e.g., surface chemistry of compound semiconductors such as indium phosphide or catalytic chemistry of transition metal oxides). In such cases, QM:QM schemes are of particular interest. In this work, a QM:QM electronic embedding model within the ONIOM (our own N-layer integrated molecular orbital molecular mechanics) extrapolation framework is presented. To define the embedding potential, we choose the real-system low-level Mulliken atomic charges. This results in a set of well-defined and unique embedding charges. However, the parametric dependence of the charges on molecular geometry complicates the energy gradient that is necessary for the efficient exploration of potential energy surfaces. We derive an efficient form for the forces where a single set of self-consistent field response equations is solved. Initial tests of the method and key algorithmic issues are discussed.
对于大型系统的化学反应进行精确的第一性原理处理仍然是电子结构理论面临的重大挑战。混合模型，如量子力学：分子力学（QM:MM）和量子力学：量子力学（QM:QM）方案，为这类研究提供了一条有前景的途径。对于许多化学领域，包括材料科学中的重要反应，分子力学或半经验方法可能不合适，或者参数不可用（例如，磷化铟等化合物半导体的表面化学或过渡金属氧化物的催化化学）。在这种情况下，QM:QM方案特别受关注。在这项工作中，提出了一种在ONIOM（我们自己的N层集成分子轨道分子力学）外推框架内的QM:QM电子嵌入模型。为了定义嵌入势，我们选择真实系统的低水平穆利肯原子电荷。这产生了一组定义明确且唯一的嵌入电荷。然而，电荷对分子几何结构的参数依赖性使有效探索势能面所需的能量梯度变得复杂。我们推导了一种有效的力的形式，其中求解了一组自洽场响应方程。讨论了该方法的初步测试和关键算法问题。
