Parameterization of Reactive Force Field: Dynamics of the [Nb₆O₁₉H_x]^(8–x)– Lindqvist Polyoxoanion in Bulk Water

Abstract

We present results on parameterization of reactive force field [van Duin, A. C. T.; Dasgupta, S.; Lorant, F.; Goddard, W. A. ReaxFF: A Reactive Force Field for Hydrocarbons. J. Phys. Chem. A 2001, 105, 9396-9409] for investigating the properties of the [Nb6O19Hx]((8-x)-) Lindqvist polyoxoanion, x = 0-8, in water. Force-field parameters were fitted to an extensive data set consisting of structures and energetics obtained at the Perdew-Burke-Ernzerhof density functional level of theory. These parameters can reasonably describe pure water structure as well as water with an excess of H(+) and OH(-) ions. Molecular dynamics simulations were performed on [Nb6O19Hx]((8-x)-), x = 0-8, submerged in bulk water at 298 K. Analysis of the MD trajectories showed facile H atom transfer between the protonated polyoxoanion core and bulk water. The number of oxygen sites labeled with an H atom was found to vary depending on the pH of the solution. Detailed analysis shows that the total number of protons at bridging (terminal), η-O (μ2-O), sites ranges from 3(1) at pH 7, to 2(0) at pH 11, to 1(0) at pH 15. These findings closely reflect available experimental measurements.

Reaction Mechanism of Nerve-Agent Hydrolysis with the Cs8Nb6O19 Lindqvist Hexaniobate Catalyst

“…Analysis of the standard Mulliken charges reveals the known trend in basicity of the various oxygen sites in the PONb: the calculated atomic charges are −0.943e, −0.994e, and −1.137e for the terminal, central, and bridging oxygen atoms, respectively. As shown in earlier experiments and calculations, the bridging oxygen is the most basic of the exposed atoms of the PONb.…”

“…Of the wealth of POM catalysts that have been synthesized over decades, − Group-V POMs with Lindqvist ion structure, particularly Nb 6 O 19 8– , are ideal candidates to act as base hydrolysis catalysts due to the high charge density of the exposed oxygen atoms . It is therefore not surprising that alkali salts of the Nb 6 O 19 8– ion have recently been reported to hydrolyze nerve agents. , Computational work on Nb 6 O 19 8– has included structural studies using DFT methods, the proposal (also with DFT methods) of an open-cage intermediate that leads to oxygen exchange with solvent measured with NMR, and a recent molecular dynamics study of the protonation of Nb 6 O 19 8– in aqueous media . However, no mechanistic studies of the base hydrolysis reactions with Nb 6 O 19 8– have been reported yet.…”

Reactive force field development for magnesium chloride hydrates and its application for seasonal heat storage

“…43 A similar peak location was reported from the ReaxFF parameters of Lindqvist Polyoxoanion in Bulk Water. 46 The first peak location for the Mg-O pair is observed at 2.0 Å, which represents the Mg-O atomic bond as shown in Fig. 10.…”

Investigation of Overall Pyrolysis Stages for Liulin Bituminous Coal by Large-Scale ReaxFF Molecular Dynamics

“…ReaxFF has a comprehensive parametrization of atomic, bonding, angle, and torsion properties, which can fully address the bond breaking, forming, and polarization effects in complicated chemistry environments . Because of its close accuracy to density functional theory (DFT), and particularly no predesignation of multiple reaction pathways required, ReaxFF MD has been applied for reaction mechanism investigations in a wide variety of materials − and fuels, − including complex coal − and biomass utilization, , which demonstrates its feasibility and potential in investigating complex reaction mechanisms. Table lists coal models and simulation results obtained using ReaxFF MD in recent years.…”