Specified supercell geometry in emc2?

Alloy Theoretic Automated Toolkit (ATAT)
1

In emc2, is there a way to set supercell dimensions
explicitly (e.g. 3x4x7) besides hoping it comes out
with a particular choice of -er?

My calculation predicts two miscibility gaps rather
than one even though a 16-site GS search predicts none.

SO, I think I have a false ground-state problem and I want
to do low-T MC on an appropriate super-cell geometry to
either find the predicted GS or prove to the fit that it
is not there.

2

A very reasonable feature request!
Solution: In emc2.c++
change

find_common_simple_supercell(&simple_supercell,lattice_only.cell,my_p_init_str->cell);
rMatrix3d mat_simple_supercell;
mat_simple_supercell.diag(to_real(simple_supercell));
iVector3d fit_sphere;
fit_sphere=find_sphere_bounding_box(lattice_only.cell*mat_simple_supercell,2.*enclosed_radius);
for (int i=0; i<3; i++) {
  simple_supercell(i)*=fit_sphere(i);
}

to

  if (file_exists("mcsupcel.in")) {
    ifstream supcelfile("mcsupcel.in");
    supcelfile >> simple_supercell;
  }
  else {
   /* piece of code you see above */
  }

And of course the file "mcsupcel.in" should contain the 3 numbers defining the supercell.
This will be in the next version…