GROMACS version:2022.3
GROMACS modification: Yes/No
Hi all,
I want to simulate CO2 using EPM2 model (the bond stretching mode is not included). After energy minimization, the following message appeared:
Energy minimization has stopped, but the forces have not converged to the
requested precision Fmax < 1000 (which may not be possible for your system).
It stopped because the algorithm tried to make a new step whose size was too
small, or there was no change in the energy since last step. Either way, we
regard the minimization as converged to within the available machine precision, given your starting configuration and EM parameters.
It shows that the system is not equilibrated. I have read the related content on the site, but I could not solve it. I appreciate any guidance or suggestions.
Here are CO2.itp and EM.mdp :
itp file for CO2:
; Carbondioxide
[ moleculetype ]
; Name nrexcl
CO2 2
[ atoms ]
; nr type resnr resid atom cgnr charge mass
1 O 1 CO2 O 1 -0.3256 15.9994
2 C 1 CO2 C 1 0.6512 12.0110
3 O 1 CO2 O 1 -0.3256 15.9994
; total charge of the molecule: 0.000
[constraints]
; i j funct doc
1 2 1 0.1149
1 3 1 0.1149
[ angles ]
; ai aj ak funct
1 2 3 1 180 1236
mdp file for energy minimization:
integrator = steep
emtol = 1000.0
emstep = 0.01
nsteps = 50000
nstlist = 10
cutoff-scheme = Verlet
ns_type = grid
coulombtype = PME
rcoulomb = 1
rvdw = 1
pbc = xyz