From: McGuire, Kelly (
Date: Wed May 23 2018 - 13:28:01 CDT

I am on the Scan Torsions step of the FFTK plugin, and my molecule has a carbon cage (amantadine). Some of the dihedral scans struggle

to finish. I set the scan to do +/- 180 for all of the dihedrals. I'm wondering what the best procedure for a cage type molecule would be

for a torsion scan. Most of them finish with the default MP2/6-31(d), but about 5 of them either end with the internal coordinates error, constraints

errors, or just stops without errors. However, if I change to HF/6-31(d), they finish with normal termination. I don't fully understand the difference between HF

and MP2 other than MP2 is a hartree-fock approximation but with an electron correlation energy correction. How much would it change my results on this

step if I used HF instead of MP2, or is there a better way to get the scan torsion to work for a cage molecule? Thanks!!

Kelly L. McGuire

PhD Scholar

Department of Physiology and Developmental Biology

Brigham Young University

LSB 3050

Provo, UT 84602