How to fix composition in emc2 code

Alloy Theoretic Automated Toolkit (ATAT)
1

Hi everyone

I want to run emc2 code under fixed composition, say 50% vs 50%. I saw -x option in emc2 command that says ‘-x=[real] set concenctration’. So I tried running emc2 by typing

‘emc2 -keV -gs=-1 -er=120 -x=0.5 -mu0=0 -dx=3e-3 -T0=100 -dT=50 -T1=100 -innerT -o=mc1.out -oss=snap.out’.

But it didn’t work. The result did not give 50% composition. Is it possible to fix the composition instead of chemical potential in emc2 code? If it is possible, did I set something wrong in the command line? I would greatly appreciate any help.

Thanks

2

I’ve been using the -cm flag for this, which enables "Canonical" mode [i.e. constant (n,V,T), as opposed to the Grand Canonical ensemble which has constant (mu,V,T)].

3

A bit more experimentation finds that in addition to -cm it is also necessary to set x=0 for a 50:50 composition. Negative values of x can be used to push the stoichiometry in the other direction, and a value of 1 causes e2mc to hang, presumably due to the statistical equivalent of a divide by zero problem.

4

Thanks for your answers!
Note that when -x=1 or -x=-1, there are no spins to flip, hence the freeze.

5

Thanks for your answer, ajjackson. It helps a lot.