Deduction of electronic properties from Gaussian output.

[Roy Jensen <royj - at - uvic.ca>]

Thanks to those of you who have aided in my use of ab initio
 calculations thus far.  With your help, I was able to get several
 transition metal cluster calculations running.
 Our lab uses mass spectrometry and spectroscopy to detect and
 characterize species. I was asked a question I cannot answer. That, of
 course led to more questions...
 0. Many texts and manuals explain how to do quantum chemistry or use
 ab initio packages. Is there an introductory reference that explains
 how to extract information from the output, Gaussian in this case?
 1. How can I tell if I need to use guess=alter?
 2. Is it reasonable to run the same complex as a singlet, triplet,
 quintet, and septet and determine the ground state multiplicity as the
 job that has the lowest energy?
 3. I generally run NBO analysis on these complexes. How do I determine
 the electronic angular momentum?
 4. Is it reasonable to _estimate_ allowed and forbidden electronic
 transitions by using the orbital energy levels provided from the
 optimized geometries? I understand that CIS and CASSCF calculations
 would provide better results.
 I have been using the UB3LYP/LANL2DZ basis set for the calculations;
 MP2/anything takes too long to converge.
 Roy Jensen