The ABINIT Users Mailing List ( CLOSED )

[jzwanzig@dal.ca]

Dear colleagues,

I find that when minimizing the forces in a crystal structure, say by doing a 
run with "ionmov 2" and "optcell 2" the resulting output structure (acell, 
rprim, xred) together breaks the original input symmetry. Never by much, but 
certain symmetry operations will have residuals of around 1E-7, which is 
worse than the built-in 1E-8 threshold. So the symmetry of the "optimized" 
structure is lower than the original input. Sometimes this is easy to detect, 
for example when all the atoms are on high symmetry positions and the acell 
variable is "optimized" to (for example) "1.11111111 1.11111111 1.11111112". 
However, some unit cells I work with have complicated shapes but still some 
symmetry. Why does the optimization run break symmetry in this way? Is there 
a setting I should be using that I don't know about?

Thanks,

Joe Zwanziger