From owner-chemistry@ccl.net Wed Dec 20 13:08:00 2006 From: "Rachel Crepo rache97]*[gmail.com" To: CCL Subject: CCL: Rydberg Natural Atomic Orbitals Message-Id: <-33287-061220130425-22110-cb9rOH0hl6UPpUGqA2JBMw#,#server.ccl.net> X-Original-From: "Rachel Crepo" Date: Wed, 20 Dec 2006 13:04:25 -0500 Sent to CCL by: "Rachel Crepo" [rache97**gmail.com] In NBO donor-aceptor squeme, how can be interpreted E2 energies to Rydberg orbitals? In some cases, these contributions are larger than conventional bonding-antibonding or LP-antibonding interactions. I am trying to explain differences in stabilities between different conformations using this squeme and the only energy differences are related to bonding-Rydberg interactions. Comments and suggestions are welcome, Best regards, Rachel From owner-chemistry@ccl.net Wed Dec 20 22:44:00 2006 From: "Mark Zottola mzottola]=[gmail.com" To: CCL Subject: CCL: hydrogen bonds AIM Message-Id: <-33288-061220223249-13282-Jvh4dLCZ2f9MUBYQXu6POw%a%server.ccl.net> X-Original-From: "Mark Zottola" Content-Type: multipart/alternative; boundary="----=_Part_32083_3607559.1166665771682" Date: Wed, 20 Dec 2006 20:49:31 -0500 MIME-Version: 1.0 Sent to CCL by: "Mark Zottola" [mzottola*o*gmail.com] ------=_Part_32083_3607559.1166665771682 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Alexander, Your English is fine, it is only the points you raise that I have issue with. I have to disagree with your assertion that there are many artifacts within the electron density analysis. I have yet to see a specious bond critical point in literally hundreds of analyses. Ring critical points nea= r bond critical points (a topological fold catastrophe), do not imply that those bond critical points are artifacts; rather reflects something about the structural stability of the molecule. If the electron density analysis is done properly, then the existence of unexpected bond critical points means there is a lack of a proper theoretical understanding of the system being examined. While I agree that Popelier's paper was a first step in aplpying electron density topology to hydrogen bonds, his criteria lack theoretical justification and cannot be reliably applied to hydrogen-bonded systems. On 12/19/06, hocquet|a|ccr.jussieu.fr wrote: > > Sent to CCL by: hocquet]=3D[ccr.jussieu.fr > My main concern about bond critical points is not the fact that "there > cannot be > a bond without a bond critical point", my issue is that there are too > often too > many bond critical points in an electronic density topology, and too many > of > them are just artefacts and not "evidence for the presence of a bond". i > agree > that Popelier's criteria can be judged as vague (and basis set dependent)= , > but > the very presence of bond paths is itself basis set dependent and not > unique. > Therefore, (and this is the credit to Popelier's approach), there is need > for a > deeper approach to bonding that the mere observation of a bond critical > point in > electronic density topology. > Sorry if my messages are not clear enough (english is not my mother > tongue). > Yours, > *********************************************** > Alexandre Hocquet > > Ecole Europ=E9enne d'Ing=E9nieurs en G=E9nie des Mat=E9riaux > 6, rue Bastien Lepage 54010 Nancy Cedex > Alexandre.Hocquet^_^eeigm.inpl-nancy.fr > http://www.eeigm.inpl-nancy.fr/~hocque23/hocquet.htm > *********************************************** > > > > -=3D This is automatically added to each message by the mailing script = =3D-> > > > ------=_Part_32083_3607559.1166665771682 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline
Alexander,
 
Your English is fine, it is only the points you raise that I have issu= e with.  I have to disagree with your assertion that there are many ar= tifacts within the electron density analysis.  I have yet to see = a specious bond critical point in literally hundreds of analyses. &nbs= p;Ring critical points near bond critical points (a topological fold c= atastrophe), do not imply that those bond critical points are art= ifacts; rather reflects something about the structural stability of the mol= ecule.  If the electron density analysis is done properly, then t= he existence of unexpected bond critical points means there is a lack = of a proper theoretical understanding of the system being examined.
 
While I agree that Popelier's paper was a first step in aplpy= ing electron density topology to hydrogen bonds, his criteria lac= k theoretical justification and cannot be reliably applied to hydrogen-bond= ed systems. =20
 

 
On 12/19/06, hocquet|a|ccr.jussieu.fr <owner-chemistry_+_ccl.net > wrote:=20
Sent to CCL by: hocquet]=3D[ ccr.jussieu.fr
My main concern about bond critical points is not the= fact that "there cannot be
a bond without a bond critical point&q= uot;, my issue is that there are too often too
many bond critical points= in an electronic density topology, and too many of
them are just artefacts and not "evidence for the presence of a bo= nd". i agree
that Popelier's criteria can be judged as vague (= and basis set dependent), but
the very presence of bond paths is itself = basis set dependent and not unique.
Therefore, (and this is the credit to Popelier's approach), there i= s need for a
deeper approach to bonding that the mere observation of a = bond critical point in
electronic density topology.
Sorry if my messa= ges are not clear enough (english is not my mother tongue).
Yours,
***********************************************
Alexandre= Hocquet

Ecole Europ=E9enne d'Ing=E9nieurs en G=E9nie des Mat=E9= riaux
6, rue Bastien Lepage 54010 Nancy Cedex
Alexandre.Hocquet^_^eei= gm.inpl-nancy.fr
http:/= /www.eeigm.inpl-nancy.fr/~hocque23/hocquet.htm
*********************= **************************



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