CCL:G: Triplet (3P) Oxygen HF energy lower than the reported HF limit?

["Kalju Kahn" <kalju ~ chem.ucsb.edu>]

 Sent to CCL by: "Kalju Kahn" [kalju+*+chem.ucsb.edu]
 Dear all,
 When I ran ROHF or UHF calculations of atomic oxygen in the triplet state,
 I get energies quite a bit lower than the reported SCF limit (-74.809398).
 For example, I use Partridge uncontracted 18s13p basis, for which
 Partridge in 1988 has reported -74.809398, in a good agreement with
 numeric HF value.  Several authors who have looked into large Gaussian
 basis sets (e.g. Jorge's generator coordinate GTOs) give similar results.
  When I run what I think is a triplet oxygen atom, I get:
 E(ROHF) -74.811377613235
 E (UHF) -74.814047051515
 It happen regardless of the program I try (Gaussian, NWChem, DIRCCR12).
 Output looks correct: I have one neutral atom with 8 electrons, 5 alpha
 and 3 beta electrons, and five occupied orbitals, three doubly occupied
 and two singly occupied).  I played with some symmetry options in NWChem
 and Roothan vs. Guest & Saunders orbitals in DIRCCR12 but the result's the
 same.  I can't figure out why the ROHF energy reported by modern programs
 is so much below the HF limit?
 I appreciate you correcting my misunderstanding here,
 P.S. NWChem input below:
 Kalju
 ---------------------------------------------------
 title "Checking oxygen triplet 3P state with NWChem"
 scratch_dir /work/nwchem/oxygen
 memory total 1000 mb
 print high
 set int:acc_std 1d-18
 set lindep:n_dep 0
 set tolguess 1e-10
 set tol2e 1e-18
 geometry units angstrom
   O      0.00000000    0.00000000   0.000000000
 end
 basis "ao basis"
 O    S
  1678789.0000000             1.0000000
 O    S
  251388.2000000              1.0000000
 O    S
   57213.7300000              1.0000000
 O    S
   16207.4400000              1.0000000
 O    S
    5288.2760000              1.0000000
 O    S
    1909.4780000              1.0000000
 O    S
     744.9231000              1.0000000
 O    S
     309.0755000              1.0000000
 O    S
     134.8645000              1.0000000
 O    S
      61.3312900              1.0000000
 O    S
      28.8379600              1.0000000
 O    S
      13.9450400              1.0000000
 O    S
       6.8990770              1.0000000
 O    S
       3.4315770              1.0000000
 O    S
       1.5398400              1.0000000
 O    S
       0.7097510              1.0000000
 O    S
       0.3230470              1.0000000
 O    S
       0.1442220              1.0000000
 O    P
    2113.5130000              1.0000000
 O    P
     500.2799000              1.0000000
 O    P
     162.5448000              1.0000000
 O    P
      62.2134300              1.0000000
 O    P
      26.3401400              1.0000000
 O    P
      11.9057400              1.0000000
 O    P
       5.6475940              1.0000000
 O    P
       2.7782140              1.0000000
 O    P
       1.3901900              1.0000000
 O    P
       0.6952810              1.0000000
 O    P
       0.3446420              1.0000000
 O    P
       0.1685380              1.0000000
 O    P
       0.0795510              1.0000000
 end
 scf
   triplet
   rohf
   thresh 3.0e-11
   tol2e  1.0e-18
   sym off
   adapt off
 end
 task scf energy
 -----------------------------------------
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Dr. Kalju Kahn
 Department of Chemistry and Biochemistry
 UC Santa Barbara, CA 93106