Subject: G: orbital energies in G94's ROHF ?

From: Konstantin Momot <[email-masked]>
Date: Tue, 18 Mar 1997 17:31:50 +42000

Dear list members,

I have a couple of questions about the meaning of one-electron energies 
in the G94 implementation of ROHF.  The questions are stated at the end of 
the post and are preceded by the description of some unexpected (for me) 
results.  

First, a couple of examples of what I'm talking about:

1.  H atom in 3-21G basis set:

    from UHF,  E total  = -.496198636018
               E e-e    = 0.000000000000D+00   (of course!)
               e(1s)    = -.49620     

    from ROHF, E total  = -.496198635984 
               E e-e    = 0.000000000000D+00  
               e(1s)    = -.11747   (exhibit 1 !!!)

    The ROHF convergence and -V/T are .3888D-05 and 1.9645, resp.  

  Clearly, 1) the ROHF result is inconsistent with 
                E tot = Sum of orbital energies - E e-e
           2) the orbital energy of the occ. MO does not have the meaning 
              of Coopman's ionization energy.

2.   Li atom in 3-21G:

     from UHF:    E total  = -7.38151    -V/T = 2.0015
                  E e-e    =  2.28290
               e(1sa)=-2.46051   e(2sa)=-0.19443  e(1sb)=-2.44387
            Sum of MO e's - E(ee)  =  -7.38171  (same as E tot, within -V/T)

     from ROHF:   E total  = -7.38151
                  E e-e    =  2.28269
               e(1s) = -2.44947     e(2s) = -0.05262   
             Sum of MO e's - E(ee) = -7.23425   (exhibit 2 !)

         The last value's difference from E total is much greater than 
       warranted by -V/T, and the 2s energy from ROHF is noticeably 
       higher than that from UHF.

So, my QUESTIONS are:

1)  What is the ROHF method implemented in G94 ?  

2)  Does it have anything to do with the method of half-electrons ?  

3)  Do the orbital energies from G94's ROHF have the meaning of Coopmans 
energies for at least some orbitals ? 

4) Those which do not have the Coopmans IP meaning - do they have any 
particular meaning in terms of E total, E e-e, J's, K's, etc. ?

Thanks in advance for all answers, leads, and suggestions.  I will summarize 
and post the replies. 

--

Konstantin Momot

[email-masked]       |"The best lack all conviction 
http://aruba.ccit.arizona.edu/     | and the worst are filled 
         ~momot/research.html      | with a passionate intensity" - Yates