[Ifeffit] P 1 space group

[scalvin at slc.edu]

Hi Bruce and others,

Back in the day, I used to use a "trick" for generating feff files for
non-crystalline, molecular substances (or small nanoclusters). I'd use a
space group of P 1 with a = b = c = 100, and alpha = beta = gamma =
90...then I could enter coordinates in hundredths of an Angstrom.

But I tried the trick recently, and the Atoms inside Artemis complains
that I should be using a cubic space group and doesn't run.

I don't know my space groups very well, but is there actually a cubic
group that doesn't have any symmetry within the unit cell? It seems to me
that a real material (not just my trick) could have an "accidentally"
cubic unit cell without being a cubic space group. Can someone who knows
crystallography better than I do confirm that?

If so, then atoms could issue a warning, but should not prevent a feff.inp
file from being generated.

Incidentally, of course I know there's a fairly trivial alternative to my
trick...I could just create the feff.inp file without using atoms (Artemis
even conveniently provides a template). But I think it's marginally easier
for some of those new to the software to use the P 1 method, because then
they don't have to think about potential lists and such.

--Scott Calvin
Sarah Lawrence College