[gmx-users] mdp file to calculate local pressure

anirban polley polley.anirban at gmail.com
Thu May 21 13:50:55 CEST 2009


Dear Sir,
             I want to calculate local pressure of the membrane (pressure
variation with z -axis). I am using gromacs-localp packages. As I see that
all types of errors coming from saying specifically the option of WALL in
.mdp file.
Actually I did not understand clearly what to do in the following options.
WALLS
; Number of walls, type, atom types, densities and box-z scale factor for
Ewald
nwall                    = 2
wall_type                = 9-3
wall_r_linpot            = -1
wall_atomtype            =
wall_density             =
wall_ewald_zfac          = 3

Could you please write clearly what to write on above options ??

I am writing here the mdp file what I am using in gromacs-localp package to
calculate local pressure.
integrator           =  sd              ; stochastic dynamics -> Langevin!
ld_seed              =  -1              ; random seed for sd
dt                   =  0.002           ; ps !
nsteps               =  50000           ; total 500/5=100 ps
nstcomm              =  1               ; freq. for cm-motion removal
tinit                =  0               ; starting time (ps)

constraints          =  all-bonds       ; constraint for all bond lengths
constraint_algorithm =  lincs           ; default
lincs_order          =  4               ; default

nstxout              =  1000            ; T(x_out) 10 ps
nstvout              =  1000            ; T(v_out) 10 ps
nstfout              =  0               ; T(f_out)
nstlog               =  250             ; energies to log (0.5 ps)
nstenergy            =  250             ; energies to energy file

ns_type              =  grid            ; nl type
nstlist              =  10              ; Freq. to update neighbour list
rlist                =  1.0             ; nm (cutoff for short-range nl)

; Periodic boundary conditions: xyz (default), no (vacuum)
; or full (infinite systems only)
pbc                      = xy

coulombtype          =  PME             ;Reaction-Field  ; Coulomb
interactions
rcoulomb             =  1.0             ;2.0             ; nm (Coulomb
cut-off!!)
epsilon_r            =  80.0            ; dielectric constant for reaction
field
vdwtype              =  Cut-off         ; Wan der Waals interactions
rvdw                 =  1.0             ; nm (LJ cut-off)
optimize_fft         =  yes

; Temperature coupling
Tcoupl               =  no              ; no effect when integrator = sd
tc-grps              =  POPC   SM   CHOL   SOL
tau_t                =  0.1   0.1   0.1   0.1
ref_t                =  296   296   296   296

; Pressure coupling
;Pcoupl = no
Pcoupl               =  berendsen
Pcoupltype           =  semiisotropic
tau_p                =  1.0    1.0       ; ps
compressibility      =  4.5e-5 4.5e-5    ; 1/bar (water: 1 atm, 300 K)
ref_p                =  1.0    1.0       ; bar

; Generate velocites in the beginning
gen_vel              =  yes
gen_temp             =  296.0
gen_seed             =  173529

;WALLS
; Number of walls, type, atom types, densities and box-z scale factor for
Ewald
nwall                    = 2
wall_type                = 9-3
wall_r_linpot            = -1
wall_atomtype            =
wall_density             =
wall_ewald_zfac          = 3

Thanks a lot in advance.
Regards,
Anirban
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