[gmx-users] question about applying surface tension

[Justin Lemkul]

On 5/7/17 2:56 PM, Ali Shomali wrote:
> Thanks so much Justin for your answer. actually I performed different
> simulations and compared the area per lipid with existing studies . for
> example I used gromacs charmm 22 for DPPC simulation and compared the
> results with Dr.Feller's paper. also I conducted a simulation on DMPC
> membrane and compared the results with existing data from
>  doi:10.1021/jp048969n. also I performed a simulation with gromacs opls
> force field on octadecanol monolayer and  checked the results with
>  doi:10.1016/j.colsurfa.2012.09.025. in all of them my area per lipid value
> changes very little and another odd thing is that even when I apply a large
> surface tension , surface compresses!

You're sort of indirectly applying a surface tension.  You've got an x-y 
pressure of 600 bar, which means the membrane will be squeezed under the 
influence of high pressure.  Note that there are actual surface tension options 
that you should probably be using.

-Justin

> I've tested all the option I could think of.
> I would appreciate it so much  if you can help me with this problem Justin
> thanks again
> Ali
>
> On Sun, May 7, 2017 at 10:34 PM, Justin Lemkul <jalemkul at vt.edu> wrote:
>
>>
>>
>> On 5/6/17 6:58 PM, Ali Shomali wrote:
>>
>>> Hello to all dear gromacs users
>>>
>>> I've faced a problem with applying surface tension , I'm , trying to model
>>> a monolayer and I've noticed whenever I apply a surface tension although
>>> my
>>> surface tension is converged  my area per lipid is wrong . i managed to
>>> model a bilayer to find out the problem and i noticed that in all my
>>> simulations my area per lipid changes are very little no matter what is
>>> surface tension nor cutoffs. but surface tension converges! i'm sending my
>>> mdp file .
>>> I will be so thankful if some one helps
>>>
>>
>> Sounds like a force field issue.  Which parameter set are you using, and
>> do you have evidence that it should respond correctly under such conditions?
>>
>> -Justin
>>
>>
>>  mdp file :
>>>
>>> title = DMPC NPT equilibration
>>> ; Run parameters
>>> integrator = md ; leap-frog integrator
>>> nsteps = 1000000 ; = 1000 ps
>>> dt = 0.001 ; 1 fs
>>> nstcomm                  = 10
>>> comm-grps                = SOL DMPC ; Remove COM for monolayers separately
>>> ; Output control
>>> nstxout = 10000 ; save coordinates every 1.0 ps
>>> nstvout = 10000 ; save velocities every 1.0 ps
>>> nstenergy = 500 ; save energies every 1.0 ps
>>> nstlog = 500 ; update log file every 1.0 ps
>>>
>>> ; Neighborsearching
>>> cutoff-scheme   = Verlet
>>> ns_type     = grid ; search neighboring grid cells
>>> nstlist     = 10 ; 20 fs, largely irrelevant with Verlet
>>> rcoulomb     = 1.4 ; short-range electrostatic cutoff (in nm)
>>> rvdw     = 1.4 ; short-range van der Waals cutoff (in nm)
>>> ; Dispersion correction
>>> DispCorr = EnerPres ; account for cut-off vdW scheme
>>> ; Electrostatics
>>> coulombtype     = PME ; Particle Mesh Ewald for long-range electrostatics
>>> ; Temperature coupling is on
>>> tcoupl = berendsen             ; modified Berendsen thermostat
>>> tc-grps = DMPC SOL ; two coupling groups - more accurate
>>> tau_t = 0.1   0.1           ; time constant, in ps
>>> ref_t = 330    330           ; reference temperature, one for each group,
>>> in K
>>> ; Pressure coupling is on
>>> Pcoupl = berendsen
>>> tau_p = 10.0
>>> compressibility = 4.5e-5 4.5e-5
>>> ref_p = 600 1.0
>>> ; Periodic boundary conditions
>>> pbc = xyz     ; 3-D PBC
>>>
>>>
>> --
>> ==================================================
>>
>> Justin A. Lemkul, Ph.D.
>> Ruth L. Kirschstein NRSA Postdoctoral Fellow
>>
>> Department of Pharmaceutical Sciences
>> School of Pharmacy
>> Health Sciences Facility II, Room 629
>> University of Maryland, Baltimore
>> 20 Penn St.
>> Baltimore, MD 21201
>>
>> jalemkul at outerbanks.umaryland.edu | (410) 706-7441
>> http://mackerell.umaryland.edu/~jalemkul
>>
>> ==================================================
>> --
>> Gromacs Users mailing list
>>
>> * Please search the archive at http://www.gromacs.org/Support
>> /Mailing_Lists/GMX-Users_List before posting!
>>
>> * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists
>>
>> * For (un)subscribe requests visit
>> https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or
>> send a mail to gmx-users-request at gromacs.org.
>>

-- 
==================================================

Justin A. Lemkul, Ph.D.
Ruth L. Kirschstein NRSA Postdoctoral Fellow

Department of Pharmaceutical Sciences
School of Pharmacy
Health Sciences Facility II, Room 629
University of Maryland, Baltimore
20 Penn St.
Baltimore, MD 21201

jalemkul at outerbanks.umaryland.edu | (410) 706-7441
http://mackerell.umaryland.edu/~jalemkul

==================================================