[gmx-users] position restraints
Christopher Neale
chris.neale at alum.utoronto.ca
Mon Apr 4 22:23:14 CEST 2016
Check the manual for freezegrps ?
_______________________________________
From: gromacs.org_gmx-users-bounces at maillist.sys.kth.se <gromacs.org_gmx-users-bounces at maillist.sys.kth.se> on behalf of Irem Altan <irem.altan at duke.edu>
Sent: 04 April 2016 15:54
To: gmx-users at gromacs.org
Subject: Re: [gmx-users] position restraints
Hi,
The .mdp file is as follows:
title = OPLS Lysozyme NVT equilibration
define = -DPOSRES ; position restrain the protein
; Run parameters
integrator = md ; leap-frog integrator
nsteps = 50000000 ; 2 * 50000 = 10 ns
dt = 0.002 ; 2 fs
; Output control
nstxout = 5000 ; save coordinates every 10 ps
nstvout = 5000 ; save velocities every 10 ps
nstxtcout = 5000
nstenergy = 5000 ; save energies every 10 ps
nstlog = 5000 ; update log file every 10 ps
; Bond parameters
continuation = no ; first dynamics run
constraint_algorithm = lincs ; holonomic constraints
constraints = all-bonds ; all bonds (even heavy atom-H bonds) constrained
lincs_iter = 1 ; accuracy of LINCS
lincs_order = 4 ; also related to accuracy
; Neighborsearching
cutoff-scheme = Verlet ;NEED TO RUN ON GPU
ns_type = grid ; search neighboring grid cells
nstlist = 5 ; 10 fs
rlist = 1.0 ; short-range neighborlist cutoff (in nm)
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 = 277 277 ; reference temperature, one for each group, in K
; Pressure coupling is off
pcoupl = no ; no pressure coupling in NVT
; Periodic boundary conditions
pbc = xyz ; 3-D PBC
; Dispersion correction
DispCorr = EnerPres ; account for cut-off vdW scheme
; Velocity generation
gen_vel = yes ; assign velocities from Maxwell distribution
gen_temp = 277 ; temperature for Maxwell distribution
gen_seed = -1 ; generate a random seed
However, it would be much better if I could freeze the protein atoms completely. How could I modify this .mdp file to do that? Also, I first do energy minimization. Do I need to freeze the protein atoms in the minimization .mdp file as well? Below are the contents of this file:
; minim.mdp - used as input into grompp to generate em.tpr
; Parameters describing what to do, when to stop and what to save
integrator = steep ; Algorithm (steep = steepest descent minimization)
emtol = 1000.0 ; Stop minimization when the maximum force < 1000.0 kJ/mol/nm
emstep = 0.00001 ; Energy step size
nsteps = 50000 ; Maximum number of (minimization) steps to perform
; Parameters describing how to find the neighbors of each atom and how to calculate the interactions
nstlist = 1 ; Frequency to update the neighbor list and long range forces
ns_type = grid ; Method to determine neighbor list (simple, grid)
rlist = 1.0 ; Cut-off for making neighbor list (short range forces)
coulombtype = PME ; Treatment of long range electrostatic interactions
rcoulomb = 1.0 ; Short-range electrostatic cut-off
rvdw = 1.0 ; Short-range Van der Waals cut-off
pbc = xyz ; Periodic Boundary Conditions (yes/no)
Best,
Irem
> On Apr 4, 2016, at 1:36 PM, Christopher Neale <chris.neale at alum.utoronto.ca> wrote:
>
> What did you set for refcoord-scaling ? How are you treating volume/pressure? Please post a full .mdp file. If you want, you can simply fix the positions and not let them move at all with freezegrps etc.
>
> ________________________________________
> From: gromacs.org_gmx-users-bounces at maillist.sys.kth.se <gromacs.org_gmx-users-bounces at maillist.sys.kth.se> on behalf of Irem Altan <irem.altan at duke.edu>
> Sent: 04 April 2016 10:23
> To: gmx-users at gromacs.org
> Subject: [gmx-users] position restraints
>
> Hi,
>
> I have a simulation in which I want to keep the protein coordinates fixed. I have tried using force constraints of strength 1000, 5000, and 10000. With 5000, there are about 100-150 atoms (out of ~1700) that drift more than 0.4A away from their equilibrium positions. This number increases when I use 10000. Is this expected behavior? What can I do to prevent the equilibrium positions from drifting away more than 0.4A?
>
> Best,
> Irem
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