[gmx-users] NVT simulation and mdp file
teklebrh at ualberta.ca
teklebrh at ualberta.ca
Wed Mar 3 18:37:08 CET 2010
Dear Gromacs Users,
I have encountered the following issues while I was running my MD
simulation. Can anybody comment on what the meaning of these notes
are. Is there anything I could do to avoid them.
NOTE 2 [file PAP.top, line unknown]:
The largest charge group contains 12 atoms.
Since atoms only see each other when the centers of geometry of the charge
groups they belong to are within the cut-off distance, too large charge
groups can lead to serious cut-off artifacts.
For efficiency and accuracy, charge group should consist of a few atoms.
For all-atom force fields use: CH3, CH2, CH, NH2, NH, OH, CO2, CO, etc.
My SOLVENT IS TOLUENE --- the PRODRG gave me a topology file with only
one group charge only.
NOTE 1 [file nvt.mdp, line unknown]:
The Berendsen thermostat does not generate the correct kinetic energy
distribution. You might want to consider using the V-rescale thermostat.
NOTE 3 [file aminoacids.dat, line 1]:
The optimal PME mesh load for parallel simulations is below 0.5
and for highly parallel simulations between 0.25 and 0.33,
for higher performance, increase the cut-off and the PME grid spacing
In addition to the above notes I have also some questions about the
NVT and NPT simulation.
1)I am using toluene as a solvent to simulate my polymer, do I need to
use the compressibility of toluene which is 9.2e-5 or the default
value 4.5e-5 1/bar.
2)What about the dielectric constant (the dielectric constant for
toluene is 2-2.4), but the default value is 80 ( I assume this is for
water- am I right).
3)Is always rvdw = 1.4 nm for GROMOS96. As a result I have to
increase my box size of the solute at the beginning to a min of 2*1.4
=2.8 ( min image convection). Is this the right way to do!
4)I run an NVT simulation to equilibrate my system for 100 ps. When I
checked my simulation at the end (successfully completed) I noticed
that the shape of my simulation box looks CIRCULAR! some how the
rectangular shape looks distorted. What does this tell! Do you guys
think something is wrong in my simulation.
5)I included the polar and aromatic hydrogens in my simulation (
ffG43a1.itp – GROMOS96.1 in PRODRG). Does these hydrogen influence my
result as the force field is a united atom force field. Or How can I
get rid of them if I want. With or without the aromatic hydrogen gave
good results ( besides lower computational cost). Does Gromos96 model
correctly aromatic-Aromatic interaction.
For more information I am posting my full NVT.mdb file below.
I really appreciate your feedback and help in advance.
thank you
Rob
#include ""
;
; File 'mdout.mdp' was generated
;
;
; LINES STARTING WITH ';' ARE COMMENTS
title = NVT equlibration ; Title of run
cpp = /usr/bin/cpp ; location of cpp on linux
; The following lines tell the program the standard locations where to
find certain files
; VARIOUS PREPROCESSING OPTIONS
; Preprocessor information: use cpp syntax.
; e.g.: -I/home/joe/doe -I/home/mary/hoe
include =
; e.g.: -DI_Want_Cookies -DMe_Too
define = -DPOSRES
; RUN CONTROL PARAMETERS
integrator = md
; Start time and timestep in ps
tinit = 0
dt = 0.002
nsteps = 50000
; For exact run continuation or redoing part of a run
; Part index is updated automatically on checkpointing (keeps files separate)
simulation_part = 1
init_step = 0
; mode for center of mass motion removal
comm-mode = Linear
; number of steps for center of mass motion removal
nstcomm = 1
; group(s) for center of mass motion removal
comm-grps =
; LANGEVIN DYNAMICS OPTIONS
; Friction coefficient (amu/ps) and random seed
bd-fric = 0
ld-seed = 1993
; ENERGY MINIMIZATION OPTIONS
; Force tolerance and initial step-size
emtol = 100
emstep = 0.01
; Max number of iterations in relax_shells
niter = 20
; Step size (ps^2) for minimization of flexible constraints
fcstep = 0
; Frequency of steepest descents steps when doing CG
nstcgsteep = 1000
nbfgscorr = 10
; TEST PARTICLE INSERTION OPTIONS
rtpi = 0.05
; OUTPUT CONTROL OPTIONS
; Output frequency for coords (x), velocities (v) and forces (f)
nstxout = 100
nstvout = 100
nstfout = 100
; Output frequency for energies to log file and energy file
nstlog = 100
nstenergy = 100
; Output frequency and precision for xtc file
nstxtcout = 100
xtc-precision = 1000
; This selects the subset of atoms for the xtc file. You can
; select multiple groups. By default all atoms will be written.
xtc-grps =
; Selection of energy groups
energygrps =
; NEIGHBORSEARCHING PARAMETERS
; nblist update frequency
nstlist = 10
; ns algorithm (simple or grid)
ns-type = Grid
; Periodic boundary conditions: xyz, no, xy
pbc = xyz
periodic_molecules = no
; nblist cut-off
rlist = 0.9
; OPTIONS FOR ELECTROSTATICS AND VDW
; Method for doing electrostatics
coulombtype = PME
rcoulomb-switch = 0
rcoulomb = 0.9
; Relative dielectric constant for the medium and the reaction field
epsilon_r = 1
epsilon_rf = 1
; Method for doing Van der Waals
vdw-type = Cut-off
; cut-off lengths
rvdw-switch = 0
rvdw = 1.4
; Apply long range dispersion corrections for Energy and Pressure
DispCorr = no
; Extension of the potential lookup tables beyond the cut-off
table-extension = 1
; Seperate tables between energy group pairs
energygrp_table =
; Spacing for the PME/PPPM FFT grid
fourierspacing = 0.12
; FFT grid size, when a value is 0 fourierspacing will be used
fourier_nx = 0
fourier_ny = 0
fourier_nz = 0
; EWALD/PME/PPPM parameters
pme_order = 4
ewald_rtol = 1e-05
ewald_geometry = 3d
epsilon_surface = 0
optimize_fft = no
; IMPLICIT SOLVENT ALGORITHM
implicit_solvent = No
; GENERALIZED BORN ELECTROSTATICS
; Algorithm for calculating Born radii
gb_algorithm = Still
; Frequency of calculating the Born radii inside rlist
nstgbradii = 1
; Cutoff for Born radii calculation; the contribution from atoms
; between rlist and rgbradii is updated every nstlist steps
rgbradii = 2
; Dielectric coefficient of the implicit solvent
gb_epsilon_solvent = 2.4
; Salt concentration in M for Generalized Born models
gb_saltconc = 0
; Scaling factors used in the OBC GB model. Default values are OBC(II)
gb_obc_alpha = 1
gb_obc_beta = 0.8
gb_obc_gamma = 4.85
; Surface tension (kJ/mol/nm^2) for the SA (nonpolar surface) part of GBSA
; The default value (2.092) corresponds to 0.005 kcal/mol/Angstrom^2.
sa_surface_tension = 2.092
; OPTIONS FOR WEAK COUPLING ALGORITHMS
; Temperature coupling
tcoupl = Berendsen ; NVT
; Groups to couple separately
tc-grps = PAP TOL
; Time constant (ps) and reference temperature (K)
tau-t = 0.1 0.1
ref-t = 300 300
; Pressure coupling
Pcoupl = No ; no presure coupling in NVT
Pcoupltype = Isotropic
; Time constant (ps), compressibility (1/bar) and reference P (bar)
tau-p = 1
compressibility = 9.2e-5
ref-p = 1
; Scaling of reference coordinates, No, All or COM
refcoord_scaling = No
; Random seed for Andersen thermostat
andersen_seed = 815131
; OPTIONS FOR QMMM calculations
QMMM = no
; Groups treated Quantum Mechanically
QMMM-grps =
; QM method
QMmethod =
; QMMM scheme
QMMMscheme = normal
; QM basisset
QMbasis =
; QM charge
QMcharge =
; QM multiplicity
QMmult =
; Surface Hopping
SH =
; CAS space options
CASorbitals =
CASelectrons =
SAon =
SAoff =
SAsteps =
; Scale factor for MM charges
MMChargeScaleFactor = 1
; Optimization of QM subsystem
bOPT =
bTS =
; SIMULATED ANNEALING
; Type of annealing for each temperature group (no/single/periodic)
annealing =
; Number of time points to use for specifying annealing in each group
annealing_npoints =
; List of times at the annealing points for each group
annealing_time =
; Temp. at each annealing point, for each group.
annealing_temp =
; GENERATE VELOCITIES FOR STARTUP RUN
gen-vel = yes ; assign velocities from Maxwell
distribution (MXD)
gen-temp = 300 ; temperature for MXD
gen-seed = 173529 ; used to initialize random
generator for random velocities
; OPTIONS FOR BONDS
constraints = all-bonds
; Type of constraint algorithm
constraint-algorithm = Lincs
; Do not constrain the start configuration
continuation = no
; Use successive overrelaxation to reduce the number of shake iterations
Shake-SOR = no
; Relative tolerance of shake
shake-tol = 0.0001
; Highest order in the expansion of the constraint coupling matrix
lincs-order = 4
; Number of iterations in the final step of LINCS. 1 is fine for
; normal simulations, but use 2 to conserve energy in NVE runs.
; For energy minimization with constraints it should be 4 to 8.
lincs-iter = 1
; Lincs will write a warning to the stderr if in one step a bond
; rotates over more degrees than
lincs-warnangle = 30
; Convert harmonic bonds to morse potentials
morse = no
; ENERGY GROUP EXCLUSIONS
; Pairs of energy groups for which all non-bonded interactions are excluded
energygrp_excl =
; WALLS
; Number of walls, type, atom types, densities and box-z scale factor
for Ewald
nwall = 0
wall_type = 9-3
wall_r_linpot = -1
wall_atomtype =
wall_density =
wall_ewald_zfac = 3
; COM PULLING
; Pull type: no, umbrella, constraint or constant_force
pull = no
; NMR refinement stuff
; Distance restraints type: No, Simple or Ensemble
disre = No
; Force weighting of pairs in one distance restraint: Conservative or Equal
disre-weighting = Conservative
; Use sqrt of the time averaged times the instantaneous violation
disre-mixed = no
disre-fc = 1000
disre-tau = 0
; Output frequency for pair distances to energy file
nstdisreout = 100
; Orientation restraints: No or Yes
orire = no
; Orientation restraints force constant and tau for time averaging
orire-fc = 0
orire-tau = 0
orire-fitgrp =
; Output frequency for trace(SD) and S to energy file
nstorireout = 100
; Dihedral angle restraints: No or Yes
dihre = no
dihre-fc = 1000
; Free energy control stuff
free-energy = no
init-lambda = 0
delta-lambda = 0
sc-alpha = 0
sc-power = 0
sc-sigma = 0.3
couple-moltype =
couple-lambda0 = vdw-q
couple-lambda1 = vdw-q
couple-intramol = no
; Non-equilibrium MD stuff
acc-grps =
accelerate =
freezegrps =
freezedim =
cos-acceleration = 0
deform =
; Electric fields
; Format is number of terms (int) and for all terms an amplitude (real)
; and a phase angle (real)
E-x =
E-xt =
E-y =
E-yt =
E-z =
E-zt =
; User defined thingies
user1-grps =
user2-grps =
userint1 = 0
userint2 = 0
userint3 = 0
userint4 = 0
userreal1 = 0
userreal2 = 0
userreal3 = 0
userreal4 = 0
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