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Two open shells

This becomes tricky in general and we give only the most important case:
shell 1
is a Roothaan case, see 6.3.2
shell 2
is one electron in an a (s) MO (nir = 1)

with parallel spin coupling of shells.

This covers e.g. the p5 s1 3P states, or the d4s1 6D states of atoms. The coupling information is given following the keyword $rohf. The (a, b) within a shell are taken from above (6.3.2), the cross term (shell 1)-(shell 2) is in this case:

a = 1    always    
b = 2    if  nnir        b = $\displaystyle {\frac{{(2n_{ir})}}{{n}}}$    if  n > nir    

where nir and n refer to shell 1.