Developing ab initio quality force fields from condensed phase quantum-mechanics/molecular-mechanics calculations through the adaptive force matching method

Abstract

A new method called adaptive force matching (AFM) has been developed that is capable of producing high quality force fields for condensed phase simulations. This procedure involves the parametrization of force fields to reproduce ab initio forces obtained from condensed phase quantum-mechanics/molecular-mechanics (QM/MM) calculations. During the procedure, the MM part of the QM/MM is iteratively improved so as to approach ab initio quality. In this work, the AFM method has been tested to parametrize force fields for liquid water so that the resulting force fields reproduce forces calculated using the ab initio MP2 and the Kohn-Sham density functional theory with the Becke-Lee-Yang-Parr (BLYP) and Becke three-parameter LYP (B3LYP) exchange correlation functionals. The AFM force fields generated in this work are very simple to evaluate and are supported by most molecular dynamics (MD) codes. At the same time, the quality of the forces predicted by the AFM force fields rivals that of very expensive ab initio calculations and are found to successfully reproduce many experimental properties. The site-site radial distribution functions (RDFs) obtained from MD simulations using the force field generated from the BLYP functional through AFM compare favorably with the previously published RDFs from Car-Parrinello MD simulations with the same functional. Technical aspects of AFM such as the optimal QM cluster size, optimal basis set, and optimal QM method to be used with the AFM procedure are discussed in this paper.

The liquid-vapor equilibria of TIP4P/2005 and BLYPSP-4F water models determined through direct simulations of the liquid-vapor interface

“…22,[41][42][43] The BLYPSP-4F model potential gives a surface tension comparable and marginally better than TIP4P/2005, underestimating the experimental value by 4.5% at 300 K. However, the γ of BLYPSP-4F water shows a weaker temperature dependence and becomes larger than the experimental value at higher temperature. The critical point of the BLYPSP-4F model is about 685 K at 190 bar using the Wegner expansion.…”

Developing accurate molecular mechanics force fields for conjugated molecular systems

“…54,55 Instead of using ab initio MD, the AFM approach uses MM FFs to generate ensembles of equilibrium structures followed by QM/MM calculations on each configuration with the MM region represented by point charges. The procedure starts with a guessed FF and is repeated until convergence of the FF parameters is reached.…”

Shortcomings of the standard Lennard–Jones dispersion term in water models, studied with force matching

“…Even if some explanations of these results are attempted (see, for example, comments on the short-range interaction potential in Ref. 2), in our opinion, a deeper analysis is due, in order to clarify some blurry aspects. All the above mentioned results have been obtained using sophisticated calculations based on the force matching (FM) algorithm, a method developed and successfully applied by Ercolessi and Adams 7 to derive a glue potential for Al.…”

“…Practically, the task consists on the minimization of a proper penalty function, usually obtained as an accumulation over many configurations and/or many particles of the least square differences between reference and effective physical quantities (originally only forces). Recently, the method has been applied for parametrizing classical force fields of a wide variety of systems, particularly water, [2][3][4][5][6][8][9][10][11][12][13][14][15][16] taking advantages also from new smarter implementations. 2,16 In this work, we will show that it is possible to systematically use the FM method to properly account for the dispersion interaction, and to obtain deeper insights on its nature.…”

“…For polar liquids, this parameter accounts also for dipole-dipole interactions (and induction, for mixtures of polar and polarizable particles) that depend on the dipoles angular orientation; nevertheless, considering the Boltzmann average over different rotational orientations, the overall C/r 6 effect has to be attractive. In recent parametrizations of force fields (FF) from ab initio reference data, [2][3][4][5][6] some of the LJ C coefficients assume negative values. Such a repulsive "dispersion" term is usually compensated by an increase of the electrostatic attraction due to slightly overestimated partial charges.…”