$closed shells a1 1-2 ( 2 ) b1 1 ( 2 ) $open shells type=1 a1 3 ( 1 ) b2 1 ( 1 ) $roothaan 1 $rohf 3a1-3a1 a = 0 b = 0 1b2-1b2 a = 0 b = 0 3a1-1b2 a = 1 b = -2