CCL: Reaction of an anion with a closed shell molecule with CASSCF

Dear Muhammed,
 Unfortunately, I can't shed any light on the technical aspects of the
 CASSCF calculation, but *qualitatively*, what you describe looks very much
 like the "curve crossing model" of chemical reactivity that has been
 by Shaik and Pross and others. If you are looking for qualitative insights,
 I would search "curve crossing model". Good luck with your
 On Thu, Jul 2, 2020 at 10:01 AM Muhammed Buyuktemiz mbtemiz3]~[ <> wrote:
 > Sent to CCL by: "Muhammed  Buyuktemiz" [mbtemiz3^]
 > Dear CCLers,
 > I am trying to investigate the electron transfer processes for a reaction
 > between an anion and a closed shell molecule. As a specific example, you
 > may consider the reaction between hydroxide and acyl chloride.
 > Initially, I am placing two species at 10 A apart from each other and
 > presume that the two are infinitely separated, i.e the ion and the acyl
 > chloride don't `feel` each other. Later on I am carrying relaxed geometry
 > optimizations by keeping inter-molecular distance r constant while r is
 > decreased in subsequent calculations.
 > However, I am having difficulty in understanding/interpreting the
 > wavefunction for the infinitely separated species. At 10 A, CASSCF
 > optimized wavefunction* shows two major configurations each with 0.60
 > coefficients. The first configuration shows what I would normally expect,
 > an OH(-) ion and a closed shell Acyl Chloride electronic structure. The
 > problem I have is related to the second configuration; This configuration
 > shows that an electron transfer takes place at 10 A and the electron is
 > located on one of the antibonding orbitals of the acyl chloride, yielding
 > OH(0) + Acyl Chloride(-) type of electronic structure.
 > I assume this is not chemically correct (since the two are infinitely
 > separated) and doesn't allow me to investigate the perturbations induced
 > when OH- approaches to Acyl Chloride**. But most importantly, since Acyl
 > Chloride now has an extra electron located on the antibonding orbital, C-
 > Cl bond breaks up in the geometry optimization calculations.***
 > My initial thought on the problem was that this might be an unbalanced
 > active space issue but various combinations also led to the same outcome.
 > I now realize this may not surprising due to the variational nature of
 > the calculation; OH(0) + Acyl Chloride(-) configuration is as
 > important/stable as the OH(-) + Acyl Chloride configuration. However this
 > sentiment alone does not fix the issue and I am stuck.
 > Is there any way to work around this issue that will allow me to
 > investigate what `happens` to orbitals on the OH- approach?
 > Any suggestions are greatly appreciated. Thank you
 > *: rest of the coefficients are smaller than 0.1.
 > **: this problem also persists for smaller/larger intermolecular
 > distances and choosing an arbitrary 10 A is not a problem.
 > ***: OH(-) -- Acyl Chloride distance is kept at 10 A.>
 Alan Shusterman
 Chemistry Department
 Reed College
 3203 SE Woodstock Blvd
 Portland, OR 97202-8199
 "Patience, persistence, and a sense of humor." Dave Barrett
 Reed College '77)