[gmx-users] RE:appropriate values fot tau_t and tau_p
Rolf Erwin Isele-Holder
Rolf.Isele at rwth-aachen.de
Tue Jul 28 11:38:02 CEST 2009
Hi,
thank you for your help, Berk.
The propertie I am looking for is the partial molar volume which can be calculated with this equation and a test particle insertion:
vi=<V^2exp(-bU)>/<Vexp(-bU)> - <V>
To find out the right mdp parameters I made test runs with a pure box of argon as vapour, so I could calculate the partial molar volume with vi=V/N and compare the results.
I tested values for tau_t and tau_p from 0.2 to 10. Then I realized that that I picked a much to small value for the isothermal compressibility and perfomed new runs with values for tau_t and tau_p from 10 to 20.
I've chosen ffG43a1 as Force Field. The mdp file I used for the simulations looks like this:
; VARIOUS PREPROCESSING OPTIONS
title = Yo
cpp = /usr/bin/cpp
include =
define =
; RUN CONTROL PARAMETERS
integrator =md
; Start time and timestep in ps
tinit = 0
dt = 0.002
nsteps = 10000000
; For exact run continuation or redoing part of a run
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
; Temperature, friction coefficient (amu/ps) and random seed
bd-fric = 0
ld-seed = 1993
; ENERGY MINIMIZATION OPTIONS
; Force tolerance and initial step-size
emtol = 0.01
emstep = 1
; Max number of iterations in relax_shells
niter = 50
; Step size (1/ps^2) for minimization of flexible constraints
fcstep = 1000
; Frequency of steepest descents steps when doing CG
nstcgsteep = 1000
nbfgscorr = 10
; OUTPUT CONTROL OPTIONS
; Output frequency for coords (x), velocities (v) and forces (f)
nstxout = 100
nstvout = 100
nstfout = 0
; Checkpointing helps you continue after crashes
nstcheckpoint = 1000
; Output frequency for energies to log file and energy file
nstlog = 250
nstenergy = 50
; Output frequency and precision for xtc file
nstxtcout = 1000
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 = 5
; ns algorithm (simple or grid)
ns_type = grid
; Periodic boundary conditions: xyz (default), no (vacuum)
; or full (infinite systems only)
pbc = xyz
; nblist cut-off
rlist = 2.5
domain-decomposition = no
; OPTIONS FOR ELECTROSTATICS AND VDW
; Method for doing electrostatics
coulombtype = Cut-off
rcoulomb-switch = 0
rcoulomb = 2.5
; Dielectric constant (DC) for cut-off or DC of reaction field
epsilon-r = 1
; Method for doing Van der Waals
vdw-type = Cut-off
; cut-off lengths
rvdw-switch = 0
rvdw = 2.5
; Apply long range dispersion corrections for Energy and Pressure
DispCorr = EnerPres
; Extension of the potential lookup tables beyond the cut-off
table-extension = 1
; 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
; 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
; Salt concentration in M for Generalized Born models
gb_saltconc = 0
; IMPLICIT SOLVENT (for use with Generalized Born electrostatics)
implicit_solvent = No
; OPTIONS FOR WEAK COUPLING ALGORITHMS
; Temperature coupling
Tcoupl = nose-hoover
; Groups to couple separately
tc-grps = System
; Time constant (ps) and reference temperature (K)
tau_t = 20
ref_t = 115.77
; Pressure coupling
Pcoupl = Parrinello-Rahman
Pcoupltype = isotropic
; Time constant (ps), compressibility (1/bar) and reference P (bar)
tau_p = 20
compressibility = 0.125
ref_p = 8
; Random seed for Andersen thermostat
andersen_seed = 815131
; SIMULATED ANNEALING
; Type of annealing for each temperature group (no/single/periodic)
annealing = no
; 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
gen_temp = 115.77
gen_seed = 1993
; OPTIONS FOR BONDS
constraints = all-bonds
; Type of constraint algorithm
constraint-algorithm = Lincs
; Do not constrain the start configuration
unconstrained-start = no
; Use successive overrelaxation to reduce the number of shake iterations
Shake-SOR = no
; Relative tolerance of shake
shake-tol = 1e-04
; 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 =
; 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) to energy file
nstorireout = 100
; Dihedral angle restraints: No, Simple or Ensemble
dihre = No
dihre-fc = 1000
dihre-tau = 0
; Output frequency for dihedral values to energy file
nstdihreout = 100
; Free energy control stuff
free-energy = no
init-lambda = 0
delta-lambda = 0
sc-alpha = 0
sc-sigma = 0.3
; Non-equilibrium MD stuff
acc-grps =
accelerate =
freezegrps =
freezedim =
cos-acceleration = 0
; 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
I hope you can find errors, that I've made.
Rolf
>Hi,
>You do not mention your the values you tried, nor other critical mdp parameters,
>nor the property you are looking for, so it is difficult to help you.
>In general, the larger you make tau_t and tau_p, the better things should get.
>tau_p should be larger than tau_t, otherwise you might induce oscillations
>by couplings between the thermo and barostat.
>
>Berk
>> Dear all,
>>
>> I'm trying to receive thermal properties of a LJ liquid by performing a NPT simulation. To ensure the simulation is in the canonic ensemble, I've chosen the Nose-Hoover thermostat and the Parrinello-Rahmann barostat. I performed several runs with different values for tau_t and tau_p. The results showed, that the property which I am looking for depends on the value of these two parameters. Does anybody know, how to chose these values to get fluctuations, which correspond to the canonical ensemble?
>>
>> Rolf
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