From owner-chemistry@ccl.net Fri Aug 25 18:28:00 2017 From: "Igors Mihailovs igorsm**cfi.lu.lv" To: CCL Subject: CCL: Vibrational sublevels along particular coordinate on PES Message-Id: <-52956-170825154931-7703-BT0yxnfi6IYTDP3nZjZOrw%server.ccl.net> X-Original-From: Igors Mihailovs Content-Language: en-US Content-Type: multipart/alternative; boundary="------------F4C63DE21E867218C5F18A4F" Date: Fri, 25 Aug 2017 22:51:44 +0300 MIME-Version: 1.0 Sent to CCL by: Igors Mihailovs [igorsm~~cfi.lu.lv] This is a multi-part message in MIME format. --------------F4C63DE21E867218C5F18A4F Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Dear computational chemistry specialists, Thank you all for your help and clarifications! Now I think I have an idea about analysing a multidimentional PES, at least from the viewpoint of statistical mechanics... Several minor questions, though: 1. Eric Hermes erichermes+/-gmail.com wrote: Second, this approach is only valid if your reaction coordinate is sufficiently flat that it can be treated classically. How flat is "sufficiently flat" PES? For example, I have barriers of 10 to 20 kcal/mol for going from 10° to 90° torsion (actually this is called internal rotation, I think). Is that "sufficiently flat"? Could someone provide examples for "not sufficiently flat" case (I mean, among well-known ones)? Do I understand it correctly that the restriction applies to cases when tunneling appears, which has also Heribert mentioned (as with proton transitions)? Can I assume that if the PES is "sufficiently flat", then the vibrational sublevels are close to each other? For the my case of internal rotation, for instance... 2. Heribert Reis hreis]|[eie.gr wrote: |the vibrational wave function of the lowest level (for simplicity) around that dihedral value| I am not sure I have understood this. In accord with the following discussion, does that mean I would need to solve for the one-dimensional problem with my 1D-PES as the well potential, which would provide me with vibrational levels, of which some will be located at the vicinity of torsion angle value NN°, some other level at MM°, etc., etc.? Thank you all again in advance! --------------F4C63DE21E867218C5F18A4F Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit Dear computational chemistry specialists,

Thank you all for your help and clarifications! Now I think I have an idea about analysing a multidimentional PES, at least from the viewpoint of statistical mechanics...

Several minor questions, though:

1.
Eric Hermes erichermes+/-gmail.com wrote:

Second, this approach is only valid if your reaction coordinate is sufficiently flat that it can
be treated classically.

How flat is "sufficiently flat" PES? For example, I have barriers of 10 to 20 kcal/mol for going from 10° to 90° torsion (actually this is called internal rotation, I think). Is that "sufficiently flat"? Could someone provide examples for "not sufficiently flat" case (I mean, among well-known ones)? Do I understand it correctly that the restriction applies to cases when tunneling appears, which has also Heribert mentioned (as with proton transitions)?

Can I assume that if the PES is "sufficiently flat", then the vibrational sublevels are close to each other? For the my case of internal rotation, for instance...

2.
Heribert Reis hreis]|[eie.gr wrote:

the vibrational wave function of the lowest level (for simplicity) around that dihedral value

I am not sure I have understood this. In accord with the following discussion, does that mean I would need to solve for the one-dimensional problem with my 1D-PES as the well potential, which would provide me with vibrational levels, of which some will be located at the vicinity of torsion angle value NN°, some other level at MM°, etc., etc.?

Thank you all again in advance!

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