Re: [AMBER] Confusion on "No Pressure"

From: Jason Swails <>
Date: Thu, 17 Dec 2015 12:27:41 -0500

On Thu, Dec 17, 2015 at 11:38 AM, Robert Molt <> wrote:

> Good morning,
> I am confused by the meaning of "no pressure" in my Amber simulation. I
> found an Amber post discussing that a value of 0.0 is not a statement of
> zero pressure, merely that there is "no" pressure. In my input file, I
> select ntb=2, ntt=3, ntp=1, which should correspond to NPT ensemble as
> far as I know (which has a pressure default of 1 bar, if I understand
> the manual). I assume I do not need to explicitly state the pressure
> given the defaults? I am using a MC barostat, if it matters? I am seeing
> a constant density just fine in my simulation (1.01 for a simulation
> with 150 mmol solute).

​All this means is that the pressure is not calculated (because the virial
is not calculated).​

​The Monte Carlo barostat does not require the virial, so it is not
computed (to save time).

All the best,

Jason M. Swails
Rutgers University
Postdoctoral Researcher
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Received on Thu Dec 17 2015 - 09:30:03 PST
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