Computational CHARMm

In this case, only two parameters (k and Iq) per atom pair are needed, and the computation of a quadratic function is less expensive. Therefore, this type of expression is used especially by biomolecular force fields (AMBER, CHARMM, GROMOS) dealing with large molecules like proteins, lipids, or DNA. 

Brooks, B.R. Bruccoleri, R.E. Olafson, B.D. States, D.J. Swaminathan, S. Karpins, M. CHARMM A program for macromolecular energy, minimization, and dynamics calculations J. Comput. Chem. 4 187-217, 1983. 

Newer, published CHARMM parameter sets override some of the combination rule generated parameters for some atom type pairs. These parameters are found in the file pointed to by the 6-12PairVDW entry for the parameter set, usually called npr.txt(dbf). The values of Ay and By for these are computed using equations (22) and (23) on page 178 by setting the 6-12PairVDWFormat entry to RStarEpsilon. 

California), Sibyl (Tripos, Missouri), ChemX (Chemical Design, UK), BioGraf (Molecular Simulations, California), Charmm/Quanta (Polygen Corp., Massachusetts), PC Model (Serena Software, Indiana), ChemLab (ChemLab Inc., Illinois), and a large number of personal computer-based packages. 

It should also be noted that a force field for a wide variety of small molecules, CHARMm (note the small m, indicating the commercial version of the program and parameters), is available [39] and has been applied to protein simulations with limited success. Efforts are currently under way to extend the CHARMm small molecule force field to make the nonbonded parameters consistent with those of the CHARMM force fields, thereby allowing for a variety of small molecules to be included in computational smdies of biological systems. 

AD MacKerell Jr, B Brooks, CL Brooks III, L Nilsson, B Roux, Y Won, M Karplus. CHARMM The energy function and its paramerization with an overview of the program. In PvR Schleyer, NL Alhnger, T Clark, J Gasteiger, PA Kollman, HP Schaefer III, PR Schreiner, eds. Encyclopedia of Computational Chemistry, Vol 1. Chichester, UK Wiley, 1998, pp 271-277. 

Patel S, Brooks CL (2004) CHARMM fluctuating charge force field for proteins I parameterization and application to bulk organic liquid simulations. J Comput Chem 25(1) 1—15... 

Brooks R, Bruccoleri RE, Olafson BD, States DJ, Swaminathan S, Karplus M (1983) Charmm A program for macromolecular energy minimization and dynamics calculations. J Comput Chem 4 187-217. 

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