GROMACS version: 2024.5
GROMACS modification: No
The new version of GROMACS documentation suggests the following modification in the md.mdp file for CHARMM36 forcefield,
constraints = h-bonds
cutoff-scheme = Verlet
vdwtype = cutoff
vdw-modifier = force-switch
rlist = 1.2
rvdw = 1.2
rvdw-switch = 1.0
coulombtype = PME
rcoulomb = 1.2
DispCorr = no
But I could not find the updated version and used the following parameters for my simulation:
title = OPLS Lysozyme NPT equilibration
; Run parameters
integrator = md ; leap-frog integrator
nsteps = 500000000 ; 2 * 500000000 = 1000000 ps (1000 ns)
dt = 0.002 ; 2 fs
; Output control
nstxout = 0 ; suppress bulky .trr file by specifying
nstvout = 0 ; 0 for output frequency of nstxout,
nstfout = 0 ; nstvout, and nstfout
nstenergy = 50000 ; save energies every 100.0 ps
nstlog = 50000 ; update log file every 100.0 ps
nstxout-compressed = 50000 ; save compressed coordinates every 100.0 ps
compressed-x-grps = System ; save the whole system
; Bond parameters
continuation = yes ; Restarting after NPT
constraint_algorithm = lincs ; holonomic constraints
constraints = h-bonds ; bonds involving H are constrained
lincs_iter = 1 ; accuracy of LINCS
lincs_order = 4 ; also related to accuracy
; Neighborsearching
cutoff-scheme = Verlet ; Buffered neighbor searching
ns_type = grid ; search neighboring grid cells
nstlist = 10 ; 20 fs, largely irrelevant with Verlet scheme
rcoulomb = 1.0 ; short-range electrostatic cutoff (in nm)
rvdw = 1.0 ; short-range van der Waals cutoff (in nm)
; Electrostatics
coulombtype = PME ; Particle Mesh Ewald for long-range electrostatics
pme_order = 4 ; cubic interpolation
fourierspacing = 0.16 ; grid spacing for FFT
; Temperature coupling is on
tcoupl = V-rescale ; modified Berendsen thermostat
tc-grps = Protein Non-Protein ; two coupling groups - more accurate
tau_t = 0.1 0.1 ; time constant, in ps
ref_t = 310 310 ; reference temperature, one for each group, in K
; Pressure coupling is on
pcoupl = Parrinello-Rahman ; Pressure coupling on in NPT
pcoupltype = isotropic ; uniform scaling of box vectors
tau_p = 2.0 ; time constant, in ps
ref_p = 1.0 ; reference pressure, in bar
compressibility = 4.5e-5 ; isothermal compressibility of water, bar^-1
; Periodic boundary conditions
pbc = xyz ; 3-D PBC
; Dispersion correction
DispCorr = EnerPres ; account for cut-off vdW scheme
; Velocity generation
gen_vel = no ; Velocity generation is off
What could be the possible implications and how could it affect my results?
Nonbonded settings are an integral part of the force field. You should use what is recommended for your chosen force field. You’re using conventional OPLS settings for CHARMM, which is wholly inappropriate.
In addition we recommend using a single temperature coupling group and tau=1 ps, as well as the c-rescale barostat with tau_p=5 ps. Using Parrinello-Rahman with a period of 2 ps can cause instabilities.