Possible bug in GMX2LAMMPS energy evaluation with waters.

[sperezconesa]

Dear developers,

I was using the program to convert from gromacs to lammps using the energy comparison and I was unable to match the angle term energies of water. My topol.top file was using the spce.itp in the GMX directory which is what most people do. I realized that the .mdp file the program uses to obtain the energies did not have the -DFLEXIBLE flag therefore eventhough lammps calculates an angular energy properly GMX was calculating it as if the molecule had SETLE/SHAKE or something like that. I got the energies to match if I modified spce.itp such that the water was considered to be flexible even -DFLEXIBLE was not raised.

I think maybe you should include this flag in the .mdp. Also an interesting feature would be to be able to select if you want to compare energies using shake or using flexible molecules.

Thank you very much for your help and congratulations on the program I find it very useful.

Sergio

[ctk3b]

Thanks for the find! That's definitely something we should be accounting for when comparing LAMMPS to GROMACS.