On 4/28/12 12:28 PM, J B wrote:
Hi,

the distance is 3.89 nm and the z-dimension is roughly 8 nm



Is the problem specific to cylinder geometry? Do other settings work? Does it make a difference if you set values for pull_r0 and pull_r1?

-Justin


 > Date: Sat, 28 Apr 2012 09:18:31 -0400
 > From: jalem...@vt.edu
 > To: gmx-users@gromacs.org
 > Subject: Re: [gmx-users] Umbrella sampling PMF, drug and membrane with
pull_geometry=cylinder
 >
 >
 >
 > On 4/28/12 5:12 AM, J B wrote:
 > > Hi.
 > >
 > > I am trying to the the PMF of transferring a drug molecule from the aqueous
 > > phase to a lipid bilayer.
 > >
 > > In order to minimize the effects of membrane undulations I tried to use
 > > pull_geometry=cylinder.
 > >
 > > Whenever I run a short simulation with umbrella sampling starting from a
 > > configuration with the drug molecule way above the bilayer
 > > the drug molecule is pulled into the bilayer rather rapidly. It appears as 
if
 > > the distance between the cylinder's COM and
 > > the drug molecule's COM is supposed to be zero since it is pulled to the 
center
 > > of the membrane.
 > >
 > > Since I apply an umbrella potential I find this weird and I would of course
like
 > > the molecule to
 > > "stay put" at that current z-position. Probably I set up the pull code 
wrong.
 > > Here are my options:
 > >
 > > pull = umbrella
 > > pull_geometry = cylinder
 > > pull_dim = N N Y
 > > pull_ngroups = 1
 > > pull_rate1 = 0.0
 > > pull_k1 = 1000
 > > pull_start = yes
 > > pull_init1 = 0.0
 > > pull_vec1 = 0.0 0.0 1.0
 > > pull_pbcatom0 = 0
 > > pull_ngroups = 1
 > > pull_group0 = DPPC
 > > pull_group1 = drug
 > >
 > > Have not decided the radii of the cylinder yet, but that is besides the
point here.
 > >
 > > I run with the 4.5.5 version and cannot figure what the problem is.
 > >
 >
 > What is the initial distance between the drug and membrane, as measured by
 > g_dist? What is the length of your unit cell along the z-axis?
 >
 > -Justin
 >
 > --
 > ========================================
 >
 > Justin A. Lemkul
 > Ph.D. Candidate
 > ICTAS Doctoral Scholar
 > MILES-IGERT Trainee
 > Department of Biochemistry
 > Virginia Tech
 > Blacksburg, VA
 > jalemkul[at]vt.edu | (540) 231-9080
 > http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
 >
 > ========================================
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--
========================================

Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin

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