GROMACS version: 2019.4
GROMACS modification: Yes/No
When alchemically changing the charge and the LJ at the same time, the electrostatic interactions can be infinite when the LJ parameters are turned off. Thus, when changing coul-lambdas and vdw-lambdas at the same time, softcore coul (sc-coul) is turned on automatically to avoid the singularity problem. In this case, the sc-coul cannot be turned off even if sc-coul=no is set.
I have a user case where instead of annihilating the vdw of a certain particle, the size of the particle is slightly modified and, thus, no singularity issue is expected. I wish to transform the charge the partial charge linearly during the transformation (thus, turn off the sc-coul) and at the same time changing the vdw with usual soft-core potential (sc-alpha != 0). I wonder if it is possible to achieve this? Thank you.