edwinb-ai / mcnpt2d

Monte Carlo simulations in the NPT ensemble

This is actually a fork of mcfort but this version works exclusively in the NPT ensemble.

It was made for the sole purpose of computing the equation of state of fluids using the NPT ensemble method and the Monte Carlo simulation technique.

It currently has several potentials implemented, but the source code must be modified by hand to enable them.

It has basic multithreading capabilities to accelerate the energy computation.

Build

To build and use this code, first create a build directory

mkdir build

then, inside this directory run the following

cmake -GNinja ..

This command expects that you have installed the ninja build system.

Then, just run

ninja

In case you only have make just run

cmake ..

and then run

make

Either way, an executable mcnpt will be created inside the build directory. This is the main executable.

Usage

The mcnpt executable expects a file called input.in with six values in it:

• Packing fraction, a value between strictly larger than 0 and strictly less than 1.0. Any value in between is acceptable. This value will determine the density of the system.
• Reduced temperature.
• Reduced pressure.
• Volume displacement, logarithm based. This is just an initial value, as the code already handles the volume displacement automatically to set it between 15-20% acceptance.
• Number of particles, an integer. The larger this value, the longer it will take to run a simulation.
• Number of Monte Carlo cycles, this is the value to use in order to equilibrate and accumulate results. The default is to use half this number for equilibration and half for averaging results.

Observables

The only observable that this code computes is the average density given a value of the reduced pressure. It also provides the standard error for this average.

With both the pressure and the density, one can obtain the equation of state for a given potential.

If you are looking for a way to compute the radial distribution function or the structure factor, please do look into mcfort.