From owner-chemistry@ccl.net Thu Aug 20 19:45:00 2009
From: "Kalju Kahn kalju-.-chem.ucsb.edu" <owner-chemistry-#-server.ccl.net>
To: CCL
Subject: CCL:G: Triplet (3P) Oxygen HF energy lower than the reported HF limit?
Message-Id: <-40039-090820192942-2485-gkCD8xIVKvdJSKsjwoJJqQ-#-server.ccl.net>
X-Original-From: "Kalju Kahn" <kalju ~ chem.ucsb.edu>
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Date: Thu, 20 Aug 2009 16:29:27 -0700
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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