Re: [AMBER] why are pres_X, pres_Y, and pres_Z different?

From: David A Case <>
Date: Mon, 28 Oct 2013 11:40:00 -0400

On Mon, Oct 28, 2013, Jose Borreguero wrote:
> The system is a solid, its constituents are octa-methyl sylsesquioxanes, a
> type of cage-molecule. I attach a picture of a 3x3x3 crystal.
> If this little crystal were to be surrounded by air, the normal pressure on
> all of its surfaces should be the same. From this I had assumed that the
> pressure components Px, Py, and Pz should be the same.

Your variations in pressure are quite small: remember that the pressure-volume
isotherms are quite steep, in that small changes in volume can lead to large
changes in pressure.

I'd rather expect values like you report with anything less than an
ideal force field; (but I don't have any real experience with this sort of
system.) [Is your system completely "dry", i.e. with no solvent molecules?]

....good luck....dac

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Received on Mon Oct 28 2013 - 09:00:03 PDT
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