[molpro-user] weird SCF convergence/reproducibility problem

[Wolfgang Eisfeld]

Jan,

The CO3 triplet state is degenerate (E'') at the D3h symmetry point. If
you treat it by RHF you induce symmetry breaking. Moreover, this is a
nasty system regarding artificial symmetry breaking even if you include
the second state component (like in NO3). These unpleasant problems are 
also encountered for distorted geometries.

You already noted that this is a strong multi-reference problem. As an 
effect, the true wave function is very different from any RHF solution. In 
fact, if I start a RHF calculation with a CASSCF initial guess for your
geometry, I cannot even reach convergence. The RHF result depends strongly 
on the initial guess and by this you can create all kinds of artificial 
solutions. Seems that Gaussian and Aces just produce different artifacts 
than Molpro.

Hope this helps,
Wolfgang

-------------------------------------------------------------------------------
PD Dr. Wolfgang Eisfeld
Bielefeld University         -  Theoretical Chemistry
Universitaetsstr. 25         -  D-33615 Bielefeld, Germany
Phone: +49-521-106 6171
Fax:   +49-521-106 6467      -  e-mail: wolfgang.eisfeld at uni-bielefeld.de
Web:   http://www.uni-bielefeld.de/chemie/tc/Eisfeld/
-------------------------------------------------------------------------------


On Sat, 26 Apr 2008, Gershom (Jan M.L.) Martin wrote:

> Dear MOLPRO gurus:
>
> Very recently I ran into a peculiar example of a transition state for which
> MOLPRO disagrees with every other code on the ROHF reference energy. See the
> simple input below. I tried every SCF convergence acceleration/coaxing trick
> in the book and a few that aren't, to no avail.
>
> The other structures on the same PES do not exhibit the problem. Does
> anybody have a clue what I am overlooking?
>
> (And yes, I know this is a highly multiref problem. Still, ROHF should give
> the same answer as Gaussian and ACES?)memory,8,m
>
> Many thanks in advance!
> Jan Martin
>
>
>    4
> E(UHF)=-262.355671204 au|Dpl=(0.5152,-0.4848,0) D||E(ROHF)=-262.338447756
> au|Dpl=(0.9471,-1.9519,0) Debye
> O    -0.832632    1.113558    0.000000
> C     0.000000    0.281073    0.000000
> O    -0.367117   -1.293021    0.000000
> O     1.199748   -0.031341    0.000000
> }
> basis=vdz
> int
> {uhf;wf,30,2,2;occ,13,3;closed,12,2}
> ! yields the correct energy
> !UHF STATE 1.2 ENERGY               -262.355671266903
> !UHF STATE 1.2 DIPOLE MOMENT           0.20268671    -0.19074510
> 0.00000000
> {hf;wf,30,2,2;occ,13,3;closed,12,2}
> ! yields a different energy, and dipole vector looks very different too
> !RHF STATE 1.2 ENERGY               -262.331395031327
> !RHF STATE 1.2 DIPOLE MOMENT           0.10470623    -0.21621532
> 0.00000000
>