Culpitt Tanner, Brorsen Kurt R, Pak Michael V, Hammes-Schiffer Sharon
Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Ave, Urbana, Illinois 61801, USA.
J Chem Phys. 2016 Jul 28;145(4):044106. doi: 10.1063/1.4958952.
Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density is separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF(-) molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.
多组分密度泛函理论（DFT）方法已得到发展，能够在同一层面上对两种类型的粒子，如电子和原子核，进行量子力学处理。在核电子轨道（NEO）方法中，所有电子和选定的原子核，通常是关键质子，都进行量子力学处理。对于在NEO框架内开发的多组分DFT方法，基于显式相关波函数设计了电子 - 质子相关泛函，并与成熟的电子交换 - 相关泛函结合使用。本文提出了一种多组分嵌入式DFT的通用理论，以实现对更大系统的精确处理。在通用理论中，总电子密度被分为两个子系统密度，分别表示为常规密度和特殊密度，并且针对这两种电子密度使用不同的电子 - 质子相关泛函。在具体实现中，特殊电子密度根据空间局部化的Kohn - Sham电子轨道来定义，并且仅对特殊电子密度包含电子 - 质子相关性。电子 - 质子相关泛函仅取决于特殊电子密度和质子密度，而电子交换 - 相关泛函取决于总电子密度。该方案包括基本的电子 - 质子相关性，这是一种相对局部的效应，以及整个系统的电子交换 - 相关性。这种多组分DFT-in-DFT嵌入理论与两种不同的电子 - 质子相关泛函和三种不同的电子交换 - 相关泛函一起应用于HCN和FHF(-)分子。结果表明，这种方法以计算上易于处理的方式提供了定性准确的核密度。该通用理论也很容易扩展到多组分系统的其他类型的划分方案。
