Number of electrons and spin multiplicity are not related. For example:
O2 molecule may be triplet or singlet. But number of electrons is the same.
If you change multiplicity, you don't change number of electrons.
You can use RHF only for closed shell singlets.
Try use small example to understand how ICHARG and MULT variables work.
If you need more help, it would be useful to see input file.
Hope this helps.
On Mon Feb 10 '14 2:53pm, Siddheshwar Chopra wrote
>I am stuck with some doubts and not able to get them clarified at all. They are::
>Say I have a CxHyMetal cluster...
>1) I understand when RHF is used and when ROHF.. Now could anyone clarify:
>TO MAKE EVEN NO. OF ELECTRONS (assuming the system has odd no. of electrons) IN SYSTEM, I CAN EITHER ADD +1 OR -1 CHARGE USING icharg... (FOR RHF)
>SECOND WAY I CAN ALSO CHANGE THE MULTIPLICITY OF THE SYSTEM AND RUN ROHF... BUT BY DOING THIS I HAVE ADDED A SPIN TO THE SYSTEM..
>Please tell me... Are not both ways same?? Don't both the ways mean that I have added an electron?
>2) I was running RHF on of such cluster with C1 symmetry and even no. of electrons. It worked well. But when I added symmetry to the i/p file and added ONLY the symmetry atoms, then I got errors: a) ODD no. of electrons. Cant run RHF and b) too many primitive bend coordinates. For around 70 atoms in total (with C1)
>How should I go about this problem now? I want to use symmetry in my case.