We have recently developed the MB-nrg (for Many-Body Energy) potential energy functions (PEFs) for halide and alkali-metal ions with water. These MB-nrg PEFs are extremely flexible functions fitted to reproduce Coupled-Cluster with Single, Double and perturbative Triple excitations (CCSD(T)) energies at the complete basis set limit, the current “gold standard” for ab initio calculations. An accurate description of the potential energy surface is needed to establish a connection between theory and experiments. In this work, we use our MB-nrg PEFs in Replica-Exchange Path Integral Molecular Dynamics (REPIMD) to study how a systematically improved description of the PES through corrections to the two-body and three-body terms of the classical underlying potential progressively reduces the gap between theoretical predictions and experimental results. Concretely, we obtained the temperature-dependent IR spectra of small Cs+(H2O)n clusters, with n=2, 3, and 4, and performed a search of the most stable isomers for each size, along with their temperature-dependent fractions in the gas phase, and compare our predictions with the experimental spectra. We also performed simulations of a single ion in bulk water, and computed structural (Radial Distribution Functions, size of the solvation shell) and spectroscopic (IR, EXAFS) properties, and compared them with data obtained by our collaborators. We show that the MB-nrg PEFs are able to predict, for any cluster or system size, any physical property of a system within chemical accuracy, which improves with the different levels of corrections to the classical underlying PEF.

Bridging theory and experiments of ion hydration with the MB-nrg potential energy functions

2019 Spring National Meeting

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