Could you attach the inpgen input? At the moment I have not yet a clear understanding on what is going on there. We have performed calculations on larger unit cells, so that is not in general a problem, though I understand that it is pretty large.

Dear Terry,

This is a problem with our k-point set generator. I assume that you want to perform the calculation at the Gamma point only. If so, you can overcome the issue by changing the last line of your inpgen input to

&kpt div1=1 div2=1 div3=1 gamma=T /
 
 

Let me also add that FLEUR might not be the perfect choice for calculating properties of molecules. FLEUR is a code for crystals, thin films, and for surfaces of crystals. Calculations on single molecules in large boxes are computationally extraordinarily expensive with it. A more natural choice for such systems would be the Siesta code.
If you nevertheless want to perform these calculations with FLEUR, you probably need several nodes of a compute cluster and it might also be a good idea to link FLEUR to the ChASE eigensolver and try that one out (maybe via linking to ELSI), though I am unsure whether calculations over multiple compute nodes can be performed with that code path at the moment. The ChASE eigensolver has strengths when the number of eigenfunctions you want to calculate is very small in comparison to the number of basis functions. Single atoms or molecules in a large box are a prototype example for this.