casscf/6-31g* opt cas(active_electrons=2,active_orbitals=2)
geom="""
C      0.000000     0.000000     0.664311
C      0.000000     0.000000    -0.664311
H      0.000000     0.923944     1.237411
H      0.000000    -0.923944     1.237411
H      0.000000     0.923944    -1.237411
H      0.000000    -0.923944    -1.237411
"""