Water models for biomolecular simulations

Modern simulation and modeling approaches to investigation of biomolecular structure and function rely heavily on a variety of methods-water models-to approximate the influence of solvent. We give a brief overview of several distinct classes of available water models, with the emphasis on the conceptual basis at each level of approximation. The main focus is on classes of models most widely used in atomistic simulations, including popular implicit and explicit solvent models. Among the latter, nonpolarizable N-point models are covered in most detail, including some recent methodological advances and nuances. Notes on practical availability and usage in biomolecular simulations are included. Atomistic simulations that were hardly possible only a short while ago have revealed significant problems that can be traced to deficiencies of most commonly used N-point water models. Recently developed models of this class approximate experimental properties of liquid water much closer than before, and show promise in practical biomolecular simulations. Obstacles to wider adoption of these more accurate water models, both technical and conceptual, are discussed. It is argued that verifying robustness of simulation results to the choice of water model can be of immediate benefit even in the absence of a clear replacement for older models; a specific strategy is proposed. The review is concluded with a discussion on how force-field development efforts can benefit from better solvent models, and vice versa. (C) 2017 Wiley Periodicals, Inc.