From owner-chemistry@ccl.net Fri Jul  3 17:32:00 2020
From: "Eric V. Patterson eric.patterson(-)stonybrook.edu" <owner-chemistry_+_server.ccl.net>
To: CCL
Subject: CCL: Reaction of an anion with a closed shell molecule with CASSCF
Message-Id: <-54135-200702181649-19088-DbrAvE4+i6DNRTopj+2Qvw_+_server.ccl.net>
X-Original-From: "Eric V. Patterson" <eric.patterson{}stonybrook.edu>
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Date: Thu, 2 Jul 2020 18:16:42 -0400
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Sent to CCL by: "Eric V. Patterson" [eric.patterson%a%stonybrook.edu]
Dear Muhammed,

You have not stated otherwise, so I assume this is a gas-phase calculation?  If so, then your observed result is logical.  Hydroxide anion is extremely unstable in the gas phase, where hydroxide radical is commonly encountered in the gas phase.  It is quite plausible that the two species “feel” each other across even 10 Angstroms of perfect vacuum.  Given the good single-electron accepting ability of the acyl group, your result is not unexpected.

Cheers,
Eric




> On Jul 2, 2020, at 4:19 AM, Muhammed Buyuktemiz mbtemiz3]~[gmail.com <owner-chemistry.:.ccl.net> wrote:
> 
> 
> Sent to CCL by: "Muhammed  Buyuktemiz" [mbtemiz3^gmail.com]
> 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.> 
>