Definition and testing of the GROMOS force-field versions 54A7 and 54B7

New parameter sets of the GROMOS biomolecular force field, 54A7 and 54B7, are introduced. These parameter sets summarise some previously published force field modifications: The 53A6 helical propensities are corrected through new φ/ψ torsional angle terms and a modification of the N–H, C=O repulsion, a new atom type for a charged −CH3 in the choline moiety is added, the Na+ and Cl− ions are modified to reproduce the free energy of hydration, and...