Development of reactive force fields using ab initio molecular dynamics simulation minimally biased to experimental data

Abstract

Incorporation of quantum mechanical electronic structure data is necessary to properly capture the physics of many chemical processes. Proton hopping in water, which involves rearrangement of chemical and hydrogen bonds, is one such example of an inherently quantum mechanical process. Standard ab initio molecular dynamics (AIMD) methods, however, do not yet accurately predict the structure of water and are therefore less than optimal for developing force fields. We have instead utilized a recently developed method which minimally biases AIMD simulations to match limited experimental data to develop novel multiscale reactive molecular dynamics (MS-RMD) force fields by using relative entropy minimization. In this paper, we present two new MS-RMD models using such a parameterization: one which employs water with harmonic internal vibrations and another which uses anharmonic water. We show that the newly developed MS-RMD models very closely reproduce the solvation structure of the hydrated excess proton in the target AIMD data. We also find that the use of anharmonic water increases proton hopping, thereby increasing the proton diffusion constant.

Correlated dynamics in aqueous proton diffusion

“…if two successive hops result in the proton being in the same location as it was initially, those hops are ignored. 9 – 11 , 16 , 18 , 30 …”

“…Voth and co-workers showed that the choice of timescale over which proton hops are considered concerted can significantly change the number of concerted hops observed. 15 , 16 They also found that the number of concerted hops was sensitive to the chosen density functional theory exchange-correlation functional and suggested that the glassy nature of water resulting from commonly used functionals could be over emphasizing concerted hops. 15 …”

“…Additionally, we note that other work has questioned the importance of concerted proton hops. 15 , 16 These questions stem from the ambiguity in defining concerted hops. Voth and co-workers showed that the choice of timescale over which proton hops are considered concerted can significantly change the number of concerted hops observed.…”

Multistate Reactive Molecular Dynamics Simulations of Proton Diffusion in Water Clusters and in the Bulk

“…One such method is based on the empirical valence bond (EVB) method. 23,24 Following this, models such as two-state EVB (TS-EVB) 25 and multi state EVB (MS-EVB) [26][27][28][29][30][31] have been developed. Within this formalism, the electronic wave function is represented as a linear combination of empirical valence bond states…”

Recent advances in quantum‐mechanical molecular dynamics simulations of proton transfer mechanism in various water‐based environments

“…Among the RFF approaches, the most popular method for revealing mechanistic details and elucidating structural and dynamical properties of the PT process is the multiple empirical valence bond (MS‐EVB) . The application of MS‐EVB to examine proton dynamics has been investigated in diverse model systems ranging from H 3 O + and OH − diffusion in bulk water, water–ice interface, and confined water environment to metal surfaces . The deliberate fitting of empirical parameters for achieving improved accuracy may be a lengthy task before starting MD simulations, thereby limiting the applicability of MS‐EVB over a broad range of systems.…”