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Need help regarding using Symmetry and mulitplicity both..

Siddheshwar Chopra
sidhusai@gmail.com


Dear Sir,
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.

Please help.



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