I am trying to run single point calculations with Gaussian 09 for a Mulliken population analysis on large graphene/graphite (940-1411 atoms) sheets/clusters.
I was having difficulty with memory issues (single CPU license) running
DFTBA for single point calculations. I have stepped my convergence (beginning with
conver=1, and increasing by reading in my previous checkpoint files). I found my results oscillating and failing.
I decided to try
scf=(qc,conver=5,maxcycle=500). This worked, which concerned me.
It not only worked, but it worked much faster than my failed
sp calculations. I know Gaussian's old default convergence for single point calculations was N=4. As my calculation was done in less than two hours compared to the days it was taking for
DIIS, I have become concerned at the accuracy of the QC using
conver=5. I cannot find anything indicating my approach is bad, but also I cannot find anything syaing my approach should yield reasonable results.
Can anyone please tell me if this approach is reasonably accurate?