hi steven,
i've been simulating a 33 AA peptide for the past two days using
implicent solvent in order to achieve a proper folding.
i haven't added counterions, however, the systems shows nice results
according to what i've expected. the mdrun command (for the extension)
for our hardware looks as follows:
mpiexec -np 4 mdrun -pd -s md.tpr -append -cpi md.cpt -deffnm md 2>&1
and here's the mdp file for the energy minimization:
define = -DFLEXIBLE
constraints = none
integrator = steep
dt = 0.001 ; ps
nsteps = 30000
vdwtype = cut-off
coulombtype = cut-off
pbc = no
nstlist = 0
ns_type = simple
rlist = 0 ; this means all-vs-all (no cut-off),
which gets expensive for bigger systems
rcoulomb = 0
rvdw = 0
comm-mode = angular
comm-grps = Protein
optimize_fft = yes
;
; Energy minimizing stuff
;
emtol = 5.0
emstep = 0.01
;
; Implicit solvent
;
implicit_solvent = GBSA
gb_algorithm = Still ; HCT ; OBC
nstgbradii = 1
rgbradii = 0 ; [nm] Cut-off for the calculation of the
Born radii. Currently must be equal to rlist
gb_epsilon_solvent = 80 ; Dielectric constant for the implicit solvent
; gb_saltconc = 0 ; Salt concentration for implicit solvent
models, currently not used
sa_algorithm = Ace-approximation
sa_surface_tension = -1
and for the md run:
define = -DPOSRESHELIX ; -DFLEXIBLE -DPOSRES
constraints = none
integrator = md
dt = 0.001 ; ps
nsteps = 1000000000 ; 100000 ps = 100 ns
nstcomm = 10
nstcalcenergy = 10
nstxout = 1000 ; frequency to write coordinates to
output trajectory
nstvout = 0 ; frequency to write velocities to output
trajectory; the last velocities are always written
nstfout = 0 ; frequency to write forces to output
trajectory
nstlog = 1000 ; frequency to write energies to log
file
nstenergy = 1000 ; frequency to write energies to edr file
vdwtype = cut-off
coulombtype = cut-off
pbc = no
nstlist = 0
ns_type = simple
rlist = 0 ; this means all-vs-all (no cut-off),
which gets expensive for bigger systems
rcoulomb = 0
rvdw = 0
comm-mode = angular
comm-grps = system
optimize_fft = yes
; V-rescale temperature coupling is on
Tcoupl = v-rescale
tau_t = 0.1
tc_grps = system
ref_t = 300
; Pressure coupling is off
Pcoupl = no
; Generate velocites is on
gen_vel = yes
gen_temp = 300
gen_seed = -1
;
; Implicit solvent
;
implicit_solvent = GBSA
gb_algorithm = Still ; HCT ; OBC
nstgbradii = 1
rgbradii = 0 ; [nm] Cut-off for the calculation of the
Born radii. Currently must be equal to rlist
gb_epsilon_solvent = 80 ; Dielectric constant for the implicit solvent
; gb_saltconc = 0 ; Salt concentration for implicit solvent
models, currently not used
sa_algorithm = Ace-approximation
sa_surface_tension = -1
best regards,
vedat
Am 28.02.2012 11:59, schrieb Steven Neumann:
Dear Gmx Users,
I am using Gromacs 4.5.4 and I would like to implement implicit
solvent for folding of my protein. I read mailing list and it is still
confusing for me.
Is it proper to use counterions within the system? If not, how can I
obtain netral system?
Do we use cut off for vdw and coulombic interactions?
What kind of integrator should be used with a timestep?
I will appreciate an mdp file for protein folding! Thank you
Steven
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