Accuracy of the force-field (FF) parameters is central to the performance of molecular modeling (MM) and molecular dynamics (MD) simulations. CHARMM is one of the most widely used FFs in the context of biological and chemical systems. To apply MM and MD methods to new systems, including in the field of drug design or micellar chemistry, new parameters need to be generated for the relevant regions of chemical space. CHARMM General Force Field (CGenFF, https://cgenff.umaryland.edu/) is a FF with an associated program for extending the FF to small molecules based on analogy of atom types and the associated parameters available in CGenFF. However, improvement of these initial parameters is often required and performing such optimization can be tedious and time consuming. In view of this, FFParam package has been designed for facilitating the parametrization process and improving both CHARMM additive and Drude FF parameters of small molecules. The package is encapsulated with a graphical user interface (GUI) created using Qt libraries (a text editor, graph plotter, molecular visualization and text to table converter) for further enhancing its ease of use. Since FF parameters are largely developed by targeting quantum mechanical (QM) data of the concerned molecule, FFParam supports Gaussian and Psi4 software for performing QM calculations, while it uses CHARMM and OpenMM for corresponding MM calculations. Partial atomic charges, atomic polarizabilities and Thole scaling parameters can be automatically fitted using a Monte Carlo Simulated Annealing (MCSA) algorithm. For automatic fitting of bonded parameter, FFParam uses an external program, LSFITPAR designed to produce robust parameters. It is anticipated that FFParam will facilitate wider use of CGenFF as well as promote future use of the Drude polarizable FF through its single unified platform.

FFParam: Standalone package for CHARMM additive and drude polarizable force field parametrization of small molecules

Macromolecular Chemistry: The Second Century

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