constraints = all-angles does not convert angles to constraints
I try to simulate united-atom propane gas (no LJ) with fixed C-C-C angle. For this I simply try to set constraints = all-angles in the mdp file, as this should:
Convert all bonds to constraints and all angles to bond-constraints.(from http://manual.gromacs.org/2019.3/user-guide/mdp-options.html#bonds)
However It does not have an effect. This i conclude from measuring the RDF between the CH3 groups, and the above option does not change the width of the peak. Also i can see the peaks in the vibrational density of states.
In the md.log i find:
The number of constraints is 4000
but it should be 6000 because there are 2000 molecules.
turning all bonds and angles into constraints...
but apparently it doesn't happen. My current guess is that this is a grompp bug.
Fix grompp constraints=all-angles with constraints
When using the mdp option constraints=all-angles, angles involving
bonds supplied as constraints in the topology would be removed,
but not replaced by angle constraints.