Theoretical Studies of Intermolecular Forces

特拉华大学的Krzysztof Szalewicz得到了化学理论、模型和计算方法计划颁发的奖项的支持，以执行分子簇、凝聚相和生物化学聚集体的理论研究。这项工作的目标是增加对依赖于分子间作用力的物理、化学和生化现象的理解。如果已知高精度的势能面或力场，这些性质可以在理论上预测。这样的表面是用PI共同开发的对称适应微扰理论(SAPT)从头开始计算的。SAPT提供了一种独特的能力，可以根据导致静电、交换、诱导和色散对相互作用能量的贡献的四种基本物理机制来解释依赖于分子间力的性质。这种解释还提供了团簇性质和组成单体的性质之间的联系。由密度泛函理论描述的基于单体的SAPT版本是目前唯一可以用于计算包含约100个原子的分子之间相互作用的方法，不确定度仅为几个百分点。SAPT正在进行进一步的开发，特别是应用本地化技术，这将进一步增加易处理系统的范围。一些旨在帮助解释从硅藻到分子晶体等系统的实验数据的应用程序正在进行中。这类应用包括开发特定于系统的力场，然后将其用于核动力学计算和分子模拟。并建立了系统普适力场。拟议的活动将导致更好地理解分子间相互作用，这些相互作用支配着凝聚相和生物聚集体的性质。研究了旨在改进研究这些相互作用的理论工具的新想法。基于第一原理的万能力场的发展有望改变生物分子模拟领域。这项活动还将产生新的压力和温度标准，帮助开发“绿色化学”，帮助探索能源，为建立大气模型提供数据，帮助了解星际分子云中的过程，指导纳米材料的开发，使生物现象的模拟更加可靠，并协助制药业预测多种形式的医疗药物。SAPT软件向所有感兴趣的研究人员免费提供，并由全世界约500个小组使用，其效率和用户友好性不断提高。

Krzysztof Szalewicz of the University of Delaware is supported by an award from the Chemical Theory, Models and Computational Methods program to perform theoretical investigations of molecular clusters, condensed phases, and biochemical aggregates. The goal of this work is to increase understanding of physical, chemical, and biochemical phenomena that depend on inter-molecular forces. These properties can be predicted theoretically if high-accuracy potential energy surfaces, or force fields, are known. Such surfaces are computed ab initio using symmetry-adapted perturbation theory (SAPT) co-developed by the PI. SAPT provides a unique ability to interpret properties dependent on intermolecular forces in terms of the four fundamental physical mechanisms that lead to the electrostatic, exchange, induction, and dispersion contributions to the interaction energies. Such interpretation also provides a connection between the cluster properties and the properties of the constituent monomers. A version of SAPT based on monomers described by density-functional theory is currently the only method which can be applied to compute interactions between molecules containing about 100 atoms with uncertainties of only a few percent. SAPT is undergoing further developments, in particular applying localization techniques that should further increase the range of tractable systems. Several applications intended to assist interpretation of experimental data for systems ranging from diatoms to molecular crystals are underway. Such applications include developments of system-specific force fields which are then used in nuclear dynamics calculations and molecular simulations. Also, system-universal force fields are developed. The proposed activity will result in a better understanding of intermolecular interactions which govern properties of condensed phases and biological aggregates. Novel ideas aimed at improvement of theoretical tools for investigations of these interactions are investigated. The development of first-principle-based universal force fields has the promise of transforming the field of biomolecular simulation. This activity will also result in new pressure and temperature standards, help in developments of "green chemistry", aid explorations of energy resources, provide data for constructing models of the atmosphere, help to understand processes in interstellar molecular clouds, guide development of nanomaterials, make simulations of biological phenomena more reliable, and assist pharmaceutical industry in predictions of polymorphic forms of medical drugs. The SAPT software available free to all interested researchers and used by about 500 groups worldwide is continuously improved in efficiency and user friendliness.