Isotopic equilibria in aqueous clusters at low temperatures: Insights from the MB-pol many-body potential

Abstract

By combining path-integrals molecular dynamics simulations with the accurate MB-pol potential energy surface, we investigate the role of alternative potential models on isotopic fractionation ratios between H and D atoms at dangling positions in water clusters at low temperatures. Our results show clear stabilizations of the lighter isotope at dangling sites, characterized by free energy differences ΔG that become comparable to or larger than kT for temperatures below ∼75 K. The comparison between these results to those previously reported using the empirical q-TIP4P/F water model [P. E. Videla et al., J. Phys. Chem. Lett. 5, 2375 (2014)] reveals that the latter Hamiltonian overestimates the H stabilization by ∼25%. Moreover, predictions from the MB-pol model are in much better agreement with measured results reported for similar isotope equilibria at ice surfaces. The dissection of the quantum kinetic energies into orthogonal directions shows that the dominant differences between the two models are to be found in the anharmonic characteristics of the potential energy surfaces along OH bond directions involved in hydrogen bonds.

Active Learning of Many-Body Configuration Space: Application to the Cs+–water MB-nrg Potential Energy Function as a Case Study

“…Within the MB-nrg framework, the water-water interactions are described by the MB-pol PEF, [9][10][11] which has been shown to correctly reproduce the properties of water 34,35 from small clusters in the gas phase, [36][37][38][39][40][41][42][43][44][45][46][47][48] to bulk water, [49][50][51][52] the air/water interface, [53][54][55][56] and ice. [57][58][59] The interactions between Cs + ions and water molecules are described through the MBE of Eq.…”

MB-Fit: Software Infrastructure for Data-Driven Many-Body Potential Energy Functions

“…56,57 A remarkable example of MB-PEFs is the MB-pol PEF for water. [58][59][60] MB-pol has been shown to correctly reproduce the properties of water, 56,61 from small gas-phase clusters [62][63][64][65][66][67][68][69][70][71][72][73] to liquid water, [74][75][76][77][78][79][80] the air/water interface, [81][82][83][84][85] , and ice. [86][87][88][89][90] The hybrid data-driven/physics-based scheme originally developed for MB-pol was later extended to generic molecules through the introduction of two families of MB-PEFs, the TTM-nrg (for "Thole-type model energy") and MB-nrg (for "many-body energy") PEFs, for halide [91][92][93] and alkali-metal [94][95][96] ions in water, molecular fluids, 97,98 and small molecules in water.…”

MB-Fit: Software Infrastructure for Data-Driven Many-Body Potential Energy Functions

“…56,57 A remarkable example of MB-PEFs is the MB-pol PEF for water. [58][59][60] MB-pol has been shown to correctly reproduce the properties of water, 56,61 from small gas-phase clusters [62][63][64][65][66][67][68][69][70][71][72][73] to liquid water, [74][75][76][77][78][79][80] the air/water interface, [81][82][83][84][85] , and ice. [86][87][88][89][90] The hybrid data-driven/physics-based scheme originally developed for MB-pol was later extended to generic molecules through the introduction of two families of MB-PEFs, the TTM-nrg (for "Thole-type model energy") and MB-nrg (for "many-body energy") PEFs, for halide [91][92][93] and alkali-metal [94][95][96] ions in water, molecular fluids, 97,98 and small molecules in water.…”