[gmx-users] Re: Pressure at constant volume

Dr. Vitaly V. Chaban vvchaban at gmail.com
Thu May 17 14:09:44 CEST 2012

> Hello everyone,
> I am trying to estimate the thermodynamic expression, dP/dw at
> constant V and T, for my polymer-solvent system. Where P is the
Hello J. -

> pressure, w is the mass fraction, V volume and T temperature. I guess
> this task can not be done by MD, as for constant Volume, pressure is
> meaningless. Since what g_energy reports is not the actual pressure
> which corresponds to that fixed Volume. Am I correct?

I do not think you are correct here. My belief is that your pressure
is just very uncertain for a [relatively] small simulated system.

> (I mean building different binary systems with different mass
> fractions of w, and measuring average P (dP/dw) while keeping T and V
> constant does not produce meaningful results by MD)

I think you have just to increase sampling to get trustworthy
pressures for a range of your systems.

Vitaly Chaban

Dr. Vitaly V. Chaban, 430 Hutchison Hall
Dept. Chemistry, University of Rochester
120 Trustee Road, Rochester, NY 14627-0216

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