[gmx-users] surface tension

David van der Spoel spoel at xray.bmc.uu.se
Thu Feb 7 08:29:42 CET 2002

On Wed, 6 Feb 2002, paloureiro wrote:

>is it possible to use the surface tension option with the Parrinello algorithm (the manual says it is not) ?
>I have been using the surface-tension with the Berendsen p couple in a DPPC bilayer, but my system behaves in a strange way:
>the use of -200 bar.nm or +200 bar.nm leads to a contraction in the XY plane (I would expect -200 bar.nm to contract and +200 bar.nm to expand the xy area).
>I have used either cut-off and PME electrostatics. I have set the compressibility to 9.8e-5 bar-1 in  xy and z.
>Any suggestion will be very helpful.
I don't know whether something could be wrong with the algorithm, but I
suggest you check the initial conditions: run without P coupling and
measure the pressure (average over > 100 ps). Chances are that your
pressure is very negative already, so the system should contract. Also,
since your compressibility is low you will have only small differences in
area with -200 and +200 bar. Measure (using g_energy) the area and surface
tension after quilibration and then compare again.

Groeten, David.
Dr. David van der Spoel, 	Biomedical center, Dept. of Biochemistry
Husargatan 3, Box 576,  	75123 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://zorn.bmc.uu.se/~spoel

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