Theoretical Chemistry Institute and Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States.
Acc Chem Res. 2015 Mar 17;48(3):548-56. doi: 10.1021/ar500272n. Epub 2015 Feb 17.
Molecular simulations have had a transformative impact on chemists' understanding of the structure and dynamics of molecular systems. Simulations can both explain and predict chemical phenomena, and they provide a unique bridge between the microscopic and macroscopic regimes. The input for such simulations is the intermolecular interactions, which then determine the forces on the constituent atoms and therefore the time evolution and equilibrium properties of the system. However, in practice, accuracy and reliability are often limited by the fidelity of the description of those very same interactions, most typically embodied approximately in mathematical form in what are known as force fields. Force fields most often utilize conceptually simple functional forms that have been parametrized to reproduce existing experimental gas phase or bulk data. Yet, reliance on empirical parametrization can sometimes introduce limitations with respect to novel chemical systems or uncontrolled errors when moving to temperatures, pressures, or environments that differ from those for which they were developed. Alternatively, it is possible to develop force fields entirely from first principles, using accurate electronic structure calculations to determine the intermolecular interactions. This introduces a new set of challenges, including the transferability of the resulting force field to related chemical systems. In response, we recently developed an alternative approach to develop force fields entirely from first-principles electronic structure calculations based on intermolecular perturbation theory. Making use of an energy decomposition analysis ensures, by construction, that the resulting force fields contain the correct balance of the various components of intermolecular interaction (exchange repulsion, electrostatics, induction, and dispersion), each treated by a functional form that reflects the underlying physics. We therefore refer to the resulting force fields as physically motivated. We find that these physically motivated force fields exhibit both high accuracy and transferability, with the latter deriving from the universality of the fundamental physical laws governing intermolecular interactions. This basic methodology has been applied to a diverse set of systems, ranging from simple liquids to nanoporous metal-organic framework materials. A key conclusion is that, in many cases, it is feasible to account for nearly all of the relevant physics of intermolecular interactions within the context of the force field. In such cases, the structural, thermodynamic, and dynamic properties of the system become naturally emergent, even in the absence of explicit parameterization to bulk properties. We also find that, quite generally, the three-body contributions to the dispersion and exchange energies in bulk liquids are crucial for quantitative accuracy in a first-principles force field, although these contributions are almost universally neglected in existing empirical force fields.
分子模拟在化学家理解分子体系的结构和动力学方面产生了变革性的影响。模拟既能解释又能预测化学现象，并且在微观和宏观领域之间提供了独特的桥梁。这种模拟的输入是分子间相互作用，然后确定组成原子上的力，从而确定系统的时间演化和平衡性质。然而，在实践中，准确性和可靠性通常受到对这些相互作用的描述的保真度的限制，这些相互作用最典型地以数学形式体现在所谓的力场中。力场最常使用概念上简单的函数形式，这些形式已被参数化以再现现有的实验气相或体相数据。然而，依靠经验参数化有时会在涉及新颖化学体系或在移动到与其开发时不同的温度、压力或环境时引入限制或不可控误差。或者，可以完全从第一性原理开发力场，使用精确的电子结构计算来确定分子间相互作用。这引入了一组新的挑战，包括将得到的力场转移到相关化学体系的可转移性。作为回应，我们最近开发了一种完全基于分子间微扰理论的第一性原理电子结构计算来开发力场的替代方法。通过使用能量分解分析，可以确保得到的力场包含分子间相互作用的各种成分（交换排斥、静电、诱导和色散）之间的正确平衡，每种成分都由反映基础物理的函数形式处理。因此，我们将得到的力场称为基于物理的。我们发现这些基于物理的力场表现出高精度和可转移性，后者源自于支配分子间相互作用的基本物理定律的普遍性。这种基本方法已经应用于从简单液体到纳米多孔金属有机骨架材料的各种体系。一个关键结论是，在许多情况下，在力场的背景下可以考虑分子间相互作用的几乎所有相关物理。在这种情况下，即使没有对体相性质的显式参数化，系统的结构、热力学和动力学性质也会自然出现。我们还发现，相当普遍地说，体相液体中色散和交换能的三体贡献对于第一性原理力场的定量精度至关重要，尽管这些贡献在现有的经验力场中几乎普遍被忽略。
