On 27/09/2011 3:48 AM, Sikandar Mashayak wrote:
Hi
I am trying to determine pressure of water at given density and
temperature using SPC/E water model. To achieve this, I am doing NVT
bulk simulations and then using g_energy I get average pressure
values. The question I have is how accurate these average pressure
predictions are?
e.g. I get average pressure of 185 bar for 300 K and 1 g/cm^3 water
density, but theoretical value for it is around 1 bar. What are the
possible reasons for this much deviation from theoretical value? Is
there anything wrong with my set up? I am using 2141 water molecules
in 4*4*4 periodic box, Nose-Hoover thermostat with 0.2ps time constant
, MD algorithm with 1fs time-step, LJ with 1.5 nm cut off and PME for
electrostatics.
The length of your simulation, and the absence of the equilibration
period from your data collection are also critical factors in obtaining
accurate converged averages, but usually neglected when people report
what might be anomalies... please see
http://www.gromacs.org/Documentation/Terminology/Pressure
Mark
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