# [gmx-users] change simulation temperature

bo.shuang bs16 at rice.edu
Wed Feb 29 02:43:26 CET 2012

```Hi, all,

I have a question about change the temperature in simulation. When I change
the ref_t and gen_temp only, (from 300 to 400) I cannot see any difference.
I am thinking if I need to change tau_t also, since diffusivity constant is
also related to temperature. Am I right?

Here is my mdp file:
title        = OPLS Lysozyme NVT equilibration
;define        = -DPOSRES    ; position restrain the protein
; Run parameters
integrator    = bd        ; leap-frog integrator
nsteps        = 500000    ; 2 * 500000 = 1000 ps
dt        = 0.002        ; 2 fs
; Output control
nstxout        = 100        ; save coordinates every 0.2 ps
nstvout        = 100        ; save velocities every 0.2 ps
nstenergy    = 100        ; save energies every 0.2 ps
nstlog        = 100        ; update log file every 0.2 ps
; Bond parameters
continuation    = yes        ; 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
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        = system    ; two coupling groups - more accurate
tau_t        = 0.01        ; time constant, in ps
ref_t        = 400         ; 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    changed
gen_temp    = 400        ; temperature for Maxwell distribution
gen_seed    = 100        ; generate a random seed
ld_seed=-1

Thank you!

Bo
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