A molecular dynamics implementation of the 3D Mercedes-Benz water model

The three-dimensional Mercedes-Benz model was recently introduced to account for the structural and thermodynamic properties of water. It treats water molecules as point-like particles with four dangling bonds in tetrahedral coordination, representing H-bonds of water. Its conceptual simplicity renders the model attractive in studies where complex behaviors emerge from H-bond interactions in water, e.g., the hydrophobic effect. A molecular dynamics (MD) implementation of the model is non-trivial and we outline here the mathematical framework of its force-field. Useful routines written in modern Fortran are also provided. This open source code is free and can easily be modified to account for different physical context. The provided code allows both serial and MPI-parallelized execution.Program summaryProgram title: CASHEW (Coarse Approach Simulator for Hydrogen-bonding Effects in Water)Catalogue identifier: AEKM_v1_0Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEKM_v1_0.htmlProgram obtainable from: CPC Program Library, Queen?s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 20 501No. of bytes in distributed program, including test data, etc.: 551 044Distribution format: tar.gzProgramming language: Fortran 90Computer: Program has been tested on desktop workstations and a Cray XT4/XT5 supercomputer.Operating system: Linux, Unix, OS XHas the code been vectorized or parallelized?: The code has been parallelized using MPI.RAM: Depends on size of system, about 5 MB for 1500 molecules.Classification: 7.7External routines: A random number generator, Mersenne Twister (http://www.math.sci.hiroshima-u.ac.jp/m-mat/MT/VERSIONS/FORTRAN/mt95.f90), is used. A copy of the code is included in the distribution.Nature of problem: Molecular dynamics simulation of a new geometric water model.Solution method: New force-field for water molecules, velocity–Verlet integration, representation of molecules as rigid particles with rotations described using quaternion algebra.Restrictions: Memory and cpu time limit the size of simulations.Additional comments: Software web site: https://gitorious.org/cashew/.Running time: Depends on the size of system. The sample tests provided only take a few seconds.