We report an ab initio, full-dimensional, potential energy surface (PES) for CO₂—H₂O, in which two-body interaction energies are fit using a basis of permutationally invariant polynomials and combined with accurate potentials for the non-interacting monomers. This approach which we have termed “plug and play” is extended here to improve the precision of the 2-body fit in the long range. This is done by combining two separate fits. One is a fit to 47 593 2-body energies in the region of strong interaction and approaching the long range, and the second one is a fit to 6244 2-body energies in the long range. The two fits have a region of overlap which permits a smooth switch from one to the other. All energies are obtained at the CCSD(T)-F12b/aug-cc-pVTZ level of theory. Properties of the full PES, i.e., stationary points, harmonic frequencies of the global minimum, etc., are shown to be in excellent agreement with direct CCSD(T)-F12b/aug-cc-pVTZ results. Diffusion Monte Carlo calculations of the dimer zero-point energy (ZPE) are performed, and a dissociation energy, D₀, of 787 cm⁻¹ is obtained using that ZPE, D_e, and the rigorous ZPEs of the monomers. Using a benchmark D_e, D₀ is 758 cm⁻¹. Vibrational self-consistent field (VSCF)/virtual state configuration interaction (VCI) MULTIMODE calculations of intramolecular fundamentals are reported and are in good agreement with available experimental results. Finally, the full dimer PES is combined with an existing ab initio water potential to develop a potential for the CO₂ hydrate clathrate CO₂(H₂O)₂₀(5¹² water cage). A full normal-mode analysis of this hydrate clathrate is reported as are local-monomer VSCF/VCI calculations of the fundamentals of CO₂.

中文翻译：

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CO ₂ -H ₂ O的两组分从头算势能面，水合物包合物的延伸，CO ₂ @（H ₂ O）₂₀以及两者的VSCF / VCI振动分析

我们报道了CO ₂ -H ₂的从头算，全尺寸，势能面（PES）O，其中两体相互作用能使用置换不变多项式的基础拟合，并与非相互作用单体的准确电势相结合。我们扩展了这种称为“即插即用”的方法，以提高2体贴合的精度。这是通过组合两个单独的拟合来完成的。第一个适合于在强相互作用区域内并接近远距离的47 593个2体能量，第二个适合于远距离上的6244个2体能量。这两个配合具有重叠区域，该重叠区域允许从一个平滑切换到另一个。所有能量均在CCSD（T）-F12b / aug-cc-pVTZ理论水平上获得。完整PES的属性，即固定点，全局最小值的谐波频率等，与CCSD（T）-F12b / aug-cc-pVTZ的直接结果非常吻合。进行二聚体零点能量（ZPE）的扩散Monte Carlo计算，并且解离能D使用该ZPE，D _e和单体的严格ZPE，可获得787 cm ^-1的₀。使用基准D _e，D ₀为758cm ^-1。报告了分子内基本原理的振动自洽场（VSCF）/虚拟状态配置相互作用（VCI）MULTIMODE计算，并与可用的实验结果高度吻合。最后，将完整的二聚体PES与现有的从头算起的水势结合，以开发出CO ₂水合物包合物CO ₂（H ₂ O）的势能₂₀（5 ¹²水笼）。据报道，该水合物包合物的完全正常模式分析以及CO ₂基本原理的局部单体VSCF / VCI计算。