[gmx-users] surface tension coupling

[Oguz Gurbulak]

Dear Gromacs Users,

I want to obtain the surface pressure–area isotherm of a surfactant
monolayer at the air–water interface by means of surface tension coupling
and make a comparison with the experimental isotherm. Therefore, I
generated a gromacs mdp file which is in below and I'm especially not sure
about tau-p and tau_t values. Could you please share your experiences and
opinions about this mdp file ? Is there anything missing or wrong in the
file ?

Thank you very much for your attention.

Best regards.



*******

; Run parameters
integrator    = md        ; leap-frog integrator
nsteps        = 2500000    ; 5000 ps = 5 ns
dt            = 0.002        ; 2 fs

; Output control
nstxout        = 1000        ; save coordinates every 2 ps
nstvout        = 1000        ; save velocities every 2 ps
nstenergy    = 1000        ; save energies every 2 ps
nstlog        = 1000        ; update log file every 2 ps

; Bond parameters
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


; Neighbor searching
cutoff-scheme   = Verlet
rlist            = 1.5        ; Neighbor list search cut-off (nm)
ns_type        = grid
nstlist        = 10        ; 20 fs
nstcomm         = 1

; Electrostatics
coulombtype        = PME    ; Particle Mesh Ewald for long-range
electrostatics
rcoulomb        = 1.5    ; short-range electrostatic cutoff (in nm)
pme_order           = 4
fourierspacing      = 0.16
ewald-rtol          = 1e-5

; Van der Waals
vdwtype = cutoff
rvdw = 1.5


; Temperature coupling
tcoupl = V-rescale
tc-grps = ABC SOL
ref_t = 300 300
tau_t = 0.1 0.1  ; ???????


; Pressure coupling
Pcoupl = berendsen
Pcoupltype = surface-tension
ref_p = 1357 1.0
tau_p = 1.0   ; ???????
compressibility = 4.5e-5 0


; Periodic boundary conditions
pbc        = xyz            ; 3-D PBC


; Velocity generation
continuation    = no        ; first dynamics run *************
gen_vel        = yes        ; assign velocities from Maxwell distribution
*************
gen_temp    = 300        ; temperature for Maxwell distribution
gen_seed    =  -1        ; generate a random seed