NPT monte carlo simulation pressure calculation

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Discussion Overview

The discussion revolves around measuring instantaneous pressure in NPT Monte Carlo simulations, focusing on the methods and challenges associated with pressure calculation during the simulation steps.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant seeks guidance on measuring instantaneous pressure at each Monte Carlo step in an NPT simulation.
  • Another participant references a Wikipedia article suggesting that pressure is conserved and proposes measuring momentum hitting the walls as a method.
  • A participant describes their use of periodic boundary conditions and expresses a desire to monitor pressure fluctuations as a function of Monte Carlo steps, noting similarities to temperature fluctuations in NVT simulations.
  • This participant mentions the virial as a potential method for measuring pressure but indicates uncertainty about its application in this context.
  • A later reply suggests that NPT Monte Carlo is a standard approach, referencing a specific text for further information and historical context.

Areas of Agreement / Disagreement

The discussion contains multiple competing views on how to measure pressure in NPT Monte Carlo simulations, with no consensus reached on the best method or approach.

Contextual Notes

Participants express uncertainty regarding the application of the virial for pressure measurement and the implications of pressure fluctuations in NPT simulations.

pyscho
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Hello all,

I have been working on an NPT monte carlo simulation. I would like to know how I can measure the instantaneous pressure of the system at each monte carlo step?
 
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I am applying periodic boundary conditions, and my atoms are sitting on their lattice sites (pretty much). I am trying to figure out the optimum lattice constant for a given pressure and temperature. However, I would like to "monitor" the pressure of the system as a function of monte carlo steps. In NVT monte carlo simulations, even the system reaches a thermal equilibrium with the heat bath, there is still fluctuations in temperature in the system (not the heat bath) besides energy fluctuations. Similar thing is also true for NPT, but I don't exactly know how to measure those fluctuations in NPT monte carlo simulation. I am digging something that has to do with virial, but not sure how to use it at the moment.
 
pyscho, NPT monte Carlo is standard now since it was introduced by S. Yip and coworkers in late 80's. Consult the text "Understanding Molecular Simulation" by Daan Frenkel for more information and references to the original papers.

Here is an amazon link for the book:
https://www.amazon.com/dp/0122673514/?tag=pfamazon01-20
 
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