Multiconfiguration Pair-Density Functional Theory for Spectroscopy and Photochemistry

在化学系的化学理论、模型和计算方法项目的支持下，芝加哥大学的劳拉·加格利亚迪教授和唐纳德·G.明尼苏达大学的Truhlar将开发多组态对密度泛函理论（MC-PDFT），并将其用于计算基态和激发态的势能面。作为合作者，两位主要研究人员正在开发计算方法，这些方法可能会在广泛的化学空间中推进知识，从催化到光化学，超分子化学，光谱学，热化学，材料化学，生物化学和大气化学。 新的计算工具有望帮助阐明实验学家发现的现象，并预测这些领域的新化学行为。这里提出的工作旨在证明量子化学方法的高水平准确性和适用性。此外，该小组将继续开发代码，以开放源码软件包的形式提供给社区，包括在文件编制方面作出相当大的努力。此外，两名高级研究员的综合专业知识将使学生和博士后受益于广泛的想法，这将有助于全面的职业准备。Truhlar正在发展具有新型波函数的对密度泛函理论（MC-PDFT），包括局域活性空间波函数，以利用某些重要类型的强电子关联的局域特性。这种方法将被进一步推广并用于探索参与催化作用的过渡金属配合物和参与光化学反应的激发态。这样的系统通常具有复杂的电子结构，即使是零级，也不能仅通过单一的电子构型，即通过在轨道中分布电子的单一方式来很好地描述。MC-PDFT可以被看作是联合收割机结合波函数理论和密度泛函理论的一种方法。特别是，该团队建议开发MC-PDFT，其目标如下：i）发展具有新型波函数的对密度泛函理论，包括局域活性空间波函数，以利用某些重要类型的强电子相关的局域特性，从而能够构建扩展的化学体系（例如金属有机框架）的精确电子结构计算，金属配体络合物和含有多个弱耦合轨道子系统的分子。ii）推导并实现MC-PDFT的解析Hessians，以便可以确定驻点是局部最小值还是鞍点，然后计算该理论水平下的振动频率。这将允许团队和社区使用MC-PDFT作为下一代工具来计算基态和激发态的势能面。（3）在不成对密度和一阶约化密度矩阵的基础上，探索新的密度泛函，以提高理论的精度。iv）将上述方法应用于过渡金属系统、光谱学和光化学。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Theory, Models and Computational Methods Program in the Chemistry Division, Professors Laura Gagliardi of the University of Chicago and Donald G. Truhlar of the University of Minnesota will develop multi-configuration pair-density functional theory (MC-PDFT) and employ it to compute potential energy surfaces for ground and excited states. As collaborators, the two principal investigators are developing computational methods that will likely advance knowledge across a broad range of chemical space, from catalysis, to photochemistry, supramolecular chemistry, spectroscopy, thermochemistry, materials chemistry, biochemistry, and atmospheric chemistry. The new computational tools are expected to help elucidate phenomena identified by experimentalists and predict new chemical behavior in these areas. The work proposed here aims to demonstratively high levels of accuracy and applicability for quantum chemical methods. Moreover, the team will continue to develop codes that will be available in open-source packages to the community, including considerable effort into documentation. Additionally, the combined expertise of two senior investigators will allow students and postdocs to benefit from a wide range of ideas that will contribute to a well-rounded career preparation.Laura Gagliardi and Donald G. Truhlar are developing pair-density functional theory (MC-PDFT) with new types of wave functions, including localized active space wave functions, in order to exploit the localized character of some important kinds of strong electron correlation. This method will be advanced and employed to explore transition metal complexes involved in catalysis and excited states involved in photochemical reactions. Such systems often have a complex electronic structure that cannot be well described even to zero order by only a single electronic configuration, that is, by a single way of distributing the electrons in orbitals. MC-PDFT can be viewed as a way to combine wave function theory (WFT) and density functional theory (DFT) to take advantage of their respective strengths. In particular, the team proposes to develop MC-PDFT with the following objectives: i) Develop pair-density functional theory with new types of wave functions, including localized active space wave functions, in order to exploit the localized character of some important kinds of strong electron correlation, so as to enable the construction of accurate electronic structure calculations for extended chemical systems such as metal-organic frameworks, metal-ligand complexes, and molecules containing multiple weakly-coupled -orbital subsystems. ii) Derive and implement analytic Hessians for MC-PDFT so that one can determine whether a stationary point is a local minimum or saddle point and then calculate vibrational frequencies at this level of theory. This will allow the team and the community to use MC-PDFT as a next-generation tool to compute potential energy surfaces for ground and excited states. iii) Explore new kinds of density functionals based on the unpaired density and the first-order reduced density matrix, to improve the accuracy of the theory. iv) Apply the methods above to transition metal systems, spectroscopy, and photochemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.