Accurate Modeling of Bromide and Iodide Hydration with Data-Driven Many-Body Potentials

Abstract

Ion–water interactions play a central role in determining the properties of aqueous systems in a wide range of environments. However, a quantitative understanding of how the hydration properties of ions evolve from small aqueous clusters to bulk solutions and interfaces remains elusive. Here, we introduce the second generation of data-driven many-body energy (MB-nrg) potential energy functions (PEFs) representing bromide–water and iodide–water interactions. The MB-nrg PEFs use permutationally invariant polynomials to reproduce two-body and three-body energies calculated at the coupled cluster level of theory, and implicitly represent all higher-body energies using classical many-body polarization. A systematic analysis of the hydration structure of small Br–(H2O) n and I–(H2O) n clusters demonstrates that the MB-nrg PEFs predict interaction energies in quantitative agreement with “gold standard” coupled cluster reference values. Importantly, when used in molecular dynamics simulations carried out in the isothermal–isobaric ensemble for single bromide and iodide ions in liquid water, the MB-nrg PEFs predict extended X-ray absorption fine structure (EXAFS) spectra that accurately reproduce the experimental spectra, which thus allows for characterizing the hydration structure of the two ions with a high level of confidence.

Hydration Structure of Na+ and K+ Ions in Solution Predicted by Data-Driven Many-Body Potentials

“…In the past years, we introduced the many-body energy (MB-nrg) theoretical/computational framework for data-driven many-body potential energy functions (PEFs). − The MB-nrg PEF of a molecular system is rigorously developed from the corresponding many-body expansion (MBE) of the system’s energy that is generally calculated at the coupled cluster level of theory, including single, double, and perturbative triple excitations, that is, CCSD­(T), which is currently considered as the “gold standard” for chemical accuracy . MB-nrg PEFs developed for alkali-metal and halide ions have been shown to accurately predict the structures, binding and interaction energies, and vibrational spectra of small X – (H 2 O) N (with X = F, Cl, Br, and I) − and M + (H 2 O) N (with M = Li, Na, K, Rb, and Cs) clusters, as well as the hydration structures of Cl – , Br – , and I – in solution. , In this study, we continue our analyses of the hydration properties of ions in solution by presenting the results of MD simulations carried out with the MB-nrg PEFs for single Na + and K + ions in solution.…”

Solvent Dynamics of Aqueous Halides before and after Photoionization

“…Despite the intensive efforts to investigate the hydration properties of the anions, experimental and theoretical results by themselves reveal an inhomogeneous picture of the halide solvation shell structure . From the theoretical side, these include density functional theory (DFT) and quantum mechanical/molecular mechanical (QM/MM) simulations, − ,,,, Car–Parrinello molecular dynamics (MD) simulations, ,,,,, classical MD simulations, ,− ,, MD simulations involving data-driven potential energy functions, , and Monte Carlo simulations . Experimentally, the hydration properties have been studied using neutron and X-ray diffraction, , X-ray absorption spectroscopy, ,,,,− and Raman and infrared (IR) spectroscopies. ,, While mostly the solvating water molecules were found oriented so as to each produce a single HO–H···X – hydrogen bond (X = Cl – , Br – , and I – ), the studies report significantly scattered first-shell X–O distances and coordination numbers: 2.70 to 3.30 Å and 4.0 to 8.9 for chloride, 3.19 to 3.40 Å and 4.2 to 8.9 for bromide, and 3.02 to 3.70 Å and 4.2 to 10.3 for iodide. ,, On the one hand, the deviating results underline the difficulty of defining the halide coordination shells due to their diffuse character and due to the fast water exchange between the first and second hydration shells (residence time is on the order of picoseconds , ).…”

“…A more comprehensive comparison between EXAFS spectra reconstructed from the radial distribution functions obtained from different theorectial approachesclassical, QM/MM, and full quantum (DFT) molecular dynamics simulationsand experimentally measured EXAFS spectra has been performed for the L 3 X-ray absorption edge of aqueous iodide by Pham et al QM/MM simulations delivered a satisfactory description of the EXAFS signal, while nonpolarizable classical simulations were somewhat less satisfactory, and DFT-based simulations performed poorly . Data-driven many-body models have equally lead to very good agreement with experimental EXAFS data for aqueous halides. , …”

“…42 Despite the intensive efforts to investigate the hydration properties of the anions, experimental and theoretical results by themselves reveal an inhomogeneous picture of the halide solvation shell structure. 82 From the theoretical side, these include density functional theory (DFT) and quantum mechanical/molecular mechanical (QM/MM) simulations, [44][45][46]49,64,67,72 Car−Parrinello molecular dynamics (MD) simulations, 41,46,47,76,77,79 classical MD simulations, 41,[48][49][50]68,78 MD simulations involving data-driven potential energy functions, 83,84 and Monte Carlo simulations. 51 Experimentally, the hydration properties have been studied using neutron and X-ray diffraction, 52,53 X-ray absorption spectroscopy, 25,38,42,45,54−61 and Raman and infrared (IR) spectroscopies.…”

Hydration Structure of Na+ and K+ Ions in Solution Predicted by Data-Driven Many-Body Potentials

“…57 A series of MB-nrg PEFs developed for alkalimetal and halide ions was shown to accurately predict the structures, binding and interaction energies, and vibrational spectra of small X − (H 2 O) N (with X = F, Cl, Br, and I) [58][59][60][61] and M + (H 2 O) N (with M = Li, Na, K, Rb, and Cs) clusters as well as the hydration structures of Cl − , Br − , and I − in solution. 62,63 In this study, we continue our analyses of the hydration properties of ions in solution by presenting the results of MD simulations carried out with the MB-nrg PEFs for single Na + and K + ions in solution.…”