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Re: [lammps-users] [EXTERNAL] how to perform grand canonical Monte Carlo simulation for binary mixture by LAMMPS?
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Re: [lammps-users] [EXTERNAL] how to perform grand canonical Monte Carlo simulation for binary mixture by LAMMPS?


From: "Thompson, Aidan" <athomps@...3...>
Date: Fri, 13 Oct 2017 22:03:51 +0000

There are a lot of complicating factors in your example. Also, it is gigantic. I can't check every possible thing you might be doing wrong. However, I did run my own tests on a modified version of in.gcmc.lj, in which I ran two gcmc fixes with two LAMMPS types with identical interaction coefficients.  The total density and pressure of the system came out slightly lower than for the 1-component case, while the excess chemical potential came out slightly higher. I think is due to the fact the ideal gas contribution to chemical potential is different by shifted by kTln(2) for 2-component case.  In any event, the numbers of types 1 and 2 are the same, within statistical noise.

 

 

--

      Aidan P. Thompson

      01444 Multiscale Science

      Sandia National Laboratories

      PO Box 5800, MS 1322      Phone: 505-844-9702

      Albuquerque, NM 87185     Fax  : 505-845-7442

      E-mail:athomps@...3... Cell : 505-218-1011

 

 

From: "chenwei@...7134..." <chenwei@...7134...>
Date: Tuesday, September 26, 2017 at 3:55 AM
To: lammps/lammps LAMMPS Users List <lammps-users@lists.sourceforge.net>
Subject: [EXTERNAL] [lammps-users] how to perform grand canonical Monte Carlo simulation for binary mixture by LAMMPS?

 

Dear LAMMPS users,

 

I try to perform grand canonical Monte Carlo simulation for binary mixture by LAMMPS.

 

I want a pure GCMC simulator.

 

Firstly, I test the program by the simulation of one component hard sphere fluid. The cutoff distance of LJ 12-6 potential is set equal to sigma, it is not a perfect hard sphere system, but the density of the system from the simulation is very close to the theoretical one.

 

However, there is a problem when I do the simulation for a binary hard-sphere mixture.  The densities predicted by the simulator are always far away from the confirmed theoretical ones.

 

The GCMC exchange is performed by these two commands in my script:

 

fix                1 O gcmc 1 1 1 1 29494 $T 3.982254 0.1 group O

fix                2 C gcmc 1 1 1 2 29494 $T 1.065682 0.1 group C

In addition, the density of the atoms handled by the second fix command is always close to zero. Here,  the density of group C is almost zero, but if I change the order of those two fix commands, then the density of group O is close to zero.

 

The LAMMPS Version is (6 Jul 2017).

 

Please find the full .in script and the .data file from the attachment.

 

Thank you very much,

 

Wei

 



Attachment: in.gcmc.lj2
Description: in.gcmc.lj2