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$closed shells

Specification of MO occupation for RHF, e.g.
 a1g     1-4                                    ( 2 )
 a2g     1                                      ( 2 )
$open shells type=1

MO occupation of open shells and number of open shells. type=1 here means that there is only a single open shell consisting e.g. of two MOs:
b2g     1                                      ( 1 )
b3g     1                                      ( 1 )

$roothaan         1
a = 1      b = 2

Roothaan parameters for the open shell, here a triplet case. define recognizes most cases and suggests good Roothaan parameters.

For further information on ROHF calculations, see the sample input in Section 18.6 and the tables of Roothaan parameters in Section 6.3.