[gmx-users] about normal pressure and constant area

Andre Farias de Moura andre at qt.dq.ufscar.br
Wed Sep 8 13:59:42 CEST 2004

hi ramon,

langmuir films imply the existence of an air/film interface
so you will need to increase your box in the z direction to
produce an evacuated region above your system. I think you
should not couple your system to any pressure bath at all,
use NVT instead. the system will have a constant area per
molecule and an average surface tension, which can be used
to compute surface pressures.

I hope it helps,

best regards,



    Dr. Andre' Farias de Moura


  Laboratorio de Quimica Teorica
Universidade Federal de Sao Carlos
     Sao Carlos - SP - Brasil


        Endereco Atual

    Grupo de Quimica Quantica
Instituto de Quimica de Sao Carlos
    Universidade de Sao Paulo
    Sao Carlos - SP - Brasil
    Telefone: 55-16-3373-8055


On Wed, 8 Sep 2004, Ramon Reigada wrote:

> We are trying to simulate a langmuir monolayer and we would like to
> adjust the normal pressure to 1at by scaling the z-axis of the box, and
> keepin the box x-y area constant (surface tension will vary). This is
> done by Lindahl et al in JCP 113, 3882 (2000).
> A possibility to do this is to choose 'surface-tension' option in
> pcoupltype and then assign a 0 x,y-compressibility, but we are sure that
> there exists a more elegant and direct way to do so.
>    thank you very much to all contibutors in the list
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