This study presents the extension of the MB-nrg (Many-Body energy) theoretical/computational framework of transferable potential energy functions (PEFs) for molecular simulations of alkali metal ion-water systems. The MB-nrg PEFs are built upon the many-body expansion of the total energy and include the explicit treatment of one-body, two-body, and three-body interactions, with all higher-order contributions described by classical induction. This study focuses on the MB-nrg two-body terms describing the full-dimensional potential energy surfaces of the M⁺(H₂O) dimers, where M⁺ = Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺. The MB-nrg PEFs are derived entirely from “first principles” calculations carried out at the explicitly correlated coupled-cluster level including single, double, and perturbative triple excitations [CCSD(T)-F12b] for Li⁺ and Na⁺ and at the CCSD(T) level for K⁺, Rb⁺, and Cs⁺. The accuracy of the MB-nrg PEFs is systematically assessed through an extensive analysis of interaction energies, structures, and harmonic frequencies for all five M⁺(H₂O) dimers. In all cases, the MB-nrg PEFs are shown to be superior to both polarizable force fields and ab initio models based on density functional theory. As previously demonstrated for halide-water dimers, the MB-nrg PEFs achieve higher accuracy by correctly describing short-range quantum-mechanical effects associated with electron density overlap as well as long-range electrostatic many-body interactions.

中文翻译：

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通过多体表示来描述离子与水之间的相互作用，以提高化学准确性。碱水二聚体势能面

这项研究提出了可转移势能函数（PEFs）的MB-nrg（多体能量）理论/计算框架的扩展，用于碱金属离子-水系统的分子模拟。MB-nrg PEF建立在总能量的多体膨胀基础上，包括对单体，两体和三体相互作用的显式处理，所有高阶贡献均由经典归纳法描述。这项研究集中于描述M ⁺（H ₂ O）二聚体的全尺寸势能面的MB-nrg两体项，其中M ⁺ = Li ⁺，Na ⁺，K ⁺，Rb ⁺和Cs ⁺。MB-nrg PEF完全来自“第一原理”计算，该计算在显式相关的耦合簇水平上进行，包括Li ⁺和Na ^+的单，双和扰动三重激发[CCSD（T）-F12b]以及在K ⁺，Rb ⁺和Cs ^+的CCSD（T）级别。通过对所有五个M ⁺（H ₂ O）二聚体的相互作用能，结构和谐波频率进行广泛的分析，可以系统地评估MB-nrg PEF的准确性。在所有情况下，MB-nrg PEF均优于极化力场和从头算基于密度泛函理论的模型。如先前针对卤化物-水二聚体所证明的那样，MB-nrg PEF通过正确描述与电子密度重叠以及长距离静电多体相互作用相关的短距离量子力学效应而实现了更高的准确度。