-------- Original Message --------
Subject:        Semiisotropic pressure coupling & comm_grps (VCM)
Date:   Mon, 26 Nov 2007 13:04:05 +0530
From:   Alok <[EMAIL PROTECTED]>
To:     <[EMAIL PROTECTED]>



Dear Sir,

Sorry for personnel mail. I have posted these question in gromacs
mailing list but I haven't got the answer. So I am sending you personally.

I have two basic questions regarding membrane protein simulation. First
regarding Semiisotropic pressure coupling (NPAT) and second regarding
comm_grpp (VCM).

1) If I want to use NPAT ensemble (x/y dimensions of bilayer to be
fixed) then is following the correct way to define?

Pcoupl                   =  Berendsen
Pcoupltype            =  semiisotropic
tau_p                     =   2.0     2.0
compressibility     =   0        4.5e-5
ref_p                     =  1.0      1.0

In some of the previous mails on same topic ref_p was defined as 0.0
1.0 in place of 1.0   1.0 even they was using compressibility 0.0
4.5e-5, that's why I am confuse. Do I have to take ref_p = 1.0   1.0 or
 0.0   1.0 when I am using compressibility 0.0   4.5e-5 (NPAT). I think
if I am taking compressibility value 0 then it doesn't matter what value
I have taken for ref_p, but I want to confirm it.

2) I want to remove center of mass translation so in following which one
is better?

    a)    comm_mode                =  Linear
           nstcomm                       =  1
           comm_grps                  =  Protein_POP ; (both protein and
lipid are together)

    b)    comm_mode                =  Linear
           nstcomm                       =  1
           comm_grps                  =  Protein POP ; (protein and
lipid separately)


Thanks a lot

Best Regards,
Alok

--
David van der Spoel, Ph.D.
Molec. Biophys. group, Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:  +46184714205. Fax: +4618511755.
[EMAIL PROTECTED]       [EMAIL PROTECTED]   http://folding.bmc.uu.se
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