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

From: Konstantin Momot <[email-masked]>
Date: Thu, 20 Mar 1997 14:53:40 +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 
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 Koopmans' 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 Koopmans 
energies for at least some orbitals ? 

4) Those which do not have the Koopmans 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