Re: [AMBER] Typo or My Confusion

From: Robert Molt <>
Date: Wed, 18 Nov 2015 10:25:10 -0500

I am confused. The manual states, on p. 310, that ntb=1 is constant
volume. On p.307, the ntp command, when it has a value other than ntp=0,
makes constant pressure. In the performance listing, on for explicit solvent PME, it says it uses
NTB=1, NTP=1. This would lead me to believe constant pressure, constant
volume (and ntt=3 makes constant temperature).

On 11/18/15 9:11 AM, David A Case wrote:
> On Tue, Nov 17, 2015, Robert Molt wrote:
>> , an estimate of the maximum system size is given for GPU types. For the
>> conditions for explicit solvent, it lists NTB=1 (which is constant
>> volume) and NTP=1 (which is constant pressure) and NTT=3 (which is the
>> canonical ensemble). I do not know of a PVT ensemble, so either I am
>> very confused on thermodynamics or there is a typo?
> I don't see the problem, but maybe it could be worded more clearly. What in
> the above description makes you think we are talking about a "PVT" ensemble,
> which I agree does not make sense?
> For historical reasons that we are reluctant to change, in Amber constant
> volume is given by ntb=1, ntp=0; to move to constant pressure, you have to
> change two variables, going to ntb=2, ntp=1. Other combinations are not
> allowed. The ntt variable is used to distinguish between constant energy and
> constant temperature simulations.
> ....hope this helps....dac
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Dr. Robert Molt Jr.
AMBER mailing list
Received on Wed Nov 18 2015 - 07:30:05 PST
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