Dear Vlad,
The reason heating with constant pressure is not recommended is that at very
low temperatures, i.e. small kinetic energies, the calculation of pressure
is very inaccurate. This can 'sometimes' lead to the barostat over
correcting which can lead to instabilities.
Once the temperature has reached around 50 - 100K or so the pressure
calculation should be fine and the barostat should then work correctly.
Thus if you start your heating from 0K it is advisable to use constant
volume. Although you can often get away with constant pressure if you have a
'weak' coupling constant or are just lucky...
I hope that helps
All the best
Ross
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> -----Original Message-----
> From: owner-amber.scripps.edu
> [mailto:owner-amber.scripps.edu] On Behalf Of Vlad Cojocaru
> Sent: Tuesday, November 29, 2005 10:51
> To: AMBER list
> Subject: AMBER: constant pressure vs. constant volume heating
>
> Dear ambers,
>
> I have had many times a question in my mind when doing
> equilibrations
> on periodic systems with explicit waters (PME). In the amber manual it
> is recommended to do the heating step (first step of equilibration) at
> constant volume rather than constant pressure....However, I have used
> both ways and the systems that I worked on equilibrated
> properly in both
> cases.
> So, I was wondering about the background of this recommendation in
> the amber manual (page 98 under NTB). Could somebody explain in few
> words why it is recommended to do the heating step at constant volume?
>
> Best wishes
> vlad
> --
>
>
> Dr. Vlad Cojocaru
> EML Research gGmbH
> Molecular and Cellular Modeling Group
> Villa Bosch
> Schloss-Wolfsbrunnenweg 33
> 69118 Heidelberg
> Germany
> Phone: +49-6221-533266
> Fax: +49-6221-533298
> e-mail: Vlad.Cojocaru.eml-r.villa-bosch.de
> <mailto:Vlad.Cojocaru.eml-r.villa-bosch.de>
> Additional info: my home page
> <http://projects.villa-bosch.de/mcm/people/cojocaru/>
>
>
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Received on Tue Nov 29 2005 - 19:53:01 PST
