Improvements to GROMACS tools#

gmx grompp now checks dihedral coefficients sum#

The sum of dihedral parameters of type 3 (i.e Ryckaert-Bellemans or Fourier dihedrals) is now checked during preprocessing. In free energy simulations, this sum must be equal in both states as it affects final results through dH/dl. Additionally, this sum should be zero when comparing potential energy values with other force field ports and simulation codes, but a non-zero sum does not otherwise affect the simulation (a simple note is emitted).

If gmx grompp rejects an interaction that was previously accepted, then change the first coefficient to make the total zero. This leading coefficient has no effect on the derivative of the energy (ie. the forces), and thus no effect on the dynamics.

No parameters in default force fields in GROMACS were affected, so none have changed.

Issue 4253