ROHF Spin contamination

[Nastasia Mauger]

Hello,

I am trying to run a ROHF calculation using the attached input. Although Molpro runs without issues, the expected ⟨S²⟩ value is not printed, even though I observe different occupations for the alpha and beta orbitals at the end of the ROHF procedure.

I would like to know how to properly run a ROHF calculation, since UHF leads to significant spin contamination in my case, and my current output does not display the expected ⟨S²⟩ value.

Thanks!

[peterso...@gmail.com]

Hi,

 

The output at the end of your ROHF,

 

Final alpha occupancy:  21  20

Final beta  occupancy:  20  20

 

Simply means that you have 1 open-shell orbital in symmetry 1. Otherwise the spatial parts of the closed-shell alpha and beta orbitals are identical. Since it is an ROHF calculation, <S2> will not be printed since the spin contamination will be zero by definition.

 

Regards,   -Kirk

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