Subject: phase/orbitals (alleged earlier posting)

From: Eric Scerri <[email-masked]>
Date: Tue, 12 Jun 2001 20:39:10 -0700

Apologies for the confusion.  In fact I failed to send my earlier 
posting which I have now corrected.  Here it is (or was).

>Dr. Richard L. Wood:
>
>>  I think he means that the idea of an orbital is NOT a mathematical
>>  concept, but a "physical", i.e. from a physics point of view,
>>  concept.
>
>Well, we apparently disagree. To me, the idea of "orbitals" in the
>case of a many electron system is basically a mathematical concept,
>since these "orbitals" have no physical reality.  But they do of
>course have physical significance, in so far as they are excellent
>approximate models in the rationalization of many kinds of physical
>and chemical behaviour.
>
>Yours, Jens >--< 
>
>=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>JENS SPANGET-LARSEN
-----------------------------------------------------

I agree with Jens regarding the mathematical nature of orbitals 
although when I recently gave a talk on this topic and presented a 
very similar position to the above I was urged to consider the 
experiments which purport to reveal phase information.  The 
implication was that I was incorrect in ruling out the possibility of 
ever observing orbitals.  This troubled me and this is what led to my 
posting.

So far the many responses I have received seem to suggest that phase 
information may be obtainable but that this still does not imply that 
individual atomic/molecular orbitals have been or ever will be 
observed in many-electron systems.

But I wonder whether the approximate nature of orbitals in 
many-electron systems might be a separate issue from whether they 
might be observable in general.

Orbitals are presumably not observable in H atoms either although 
within a non-relativistic Schrodinger treatment they are defined 
exactly.  Should we perhaps separate the approximate nature of 
orbitals in N electron systems from the more categorical aspect that 
an orbital is not an actual electron path, even in H, or He+, or Li2+ 
etc although the term "orbital" wrongly suggests that it might be.

So until somebody observes phase information in any one-electron 
system I think I can continue to insist that orbitals cannot be 
observed.

eric scerri
-- 

Dr. Eric Scerri ,
UCLA,
Department of Chemistry & Biochemistry,
607 Charles E. Young Drive East,
Los Angeles,  CA 90095-1569
USA

E-mail :   [email-masked]
tel:  310 206 7443
fax:  310 206 2061
Web Page:    http://www.chem.ucla.edu/dept/Faculty/scerri/index.html

Editor  of  Foundations of Chemistry
http://www.wkap.nl/journalhome.htm/1386-4238

Also see International Society for the Philosophy of Chemistry
http://www.georgetown.edu/earleyj/ISPC.html

---

From: "Dr. Richard L. Wood" <[email-masked]>
Date: Wed, 13 Jun 2001 12:38:56 -0400

> posting which I have now corrected.  Here it is (or was).

But isn't the actual "orbital" the result of taking a MATHEMATICAL
function and squaring it to get a "probability density"?

And, as such, isn't this "probability density" also a MTHEMATICAL construct?

Later, someone related the "probability density" with the concept of an
"orbital".
And wasn't this someone a physicist?

Please correct me if I'm incocrrect.

Richard

--
Richard L. Wood, Ph. D.
Physical/Computational Chemist
Post-doctoral Associate
Cornell University, Ithaca, NY 14853

---

From: Maurice Cafiero <[email-masked]>
Date: Wed, 13 Jun 2001 19:51:31 +0000

hello:
    I apologize for dragging this out, but I would like to add someting to this
discussion.
I attribute the widely accepted yet *wrong* idea that orbitals are real to the
fact that within HF theory,
a physical property can be attributed to the orbital enegies (IP, EA). But just
because the enegies have a
(weak) predictive power does not mean that orbitals are real.  How "physical"
or "mathematical" is it
to take one multiplicative term out of a wavefunction and square it and expect
to get something meaningful?

Lewis dot structures have a somewhat predictive power, but are we going to
start looking for experimental evidence
for lewis dots?

--
Mauricio Cafiero
Doctoral Candidate : Theoretical
                     and Computational
                     Quantum Chemistry
Department of Chemistry
University of Arizona