|Date:||Wed, 25 Oct 2017 09:05:50 +0800 (GMT+08:00)|
Dear Aidan P. Thompson,
I fixed this problem by using two different random number seeds in those two commands:
fix 1 O gcmc 1 1 1 1 29494 $T 9.0 0.1 group O
fix 2 C gcmc 1 1 1 2 271828 $T 9.0 0.1 group C
From:"Thompson, Aidan" <athomps@...3...>
Sent Time:2017-10-14 06:03:51 (Saturday)
To: "chenwei@...7134..." <chenwei@...7134...>, "firstname.lastname@example.org" <email@example.com>
Subject: Re: [EXTERNAL] [lammps-users] how to perform grand canonical Monte Carlo simulation for binary mixture by LAMMPS?
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
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,