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From: Wai-To Chan <chan@curl.gkcl.yorku.ca>
Message-Id: <200106100158.f5A1wVC26991@curl.gkcl.yorku.ca>
Subject: phase information/orbitals question
To: chemistry@ccl.net
Date: Sat, 9 Jun 2001 21:58:31 -0400 (EDT)
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<<<<<<
At the risk of re-opening the debate on the observation of orbitals,

I recently had a communication informing me that several experiments 
have provided  phase information involving electrons in atoms and 
molecules and that this can be regarded as evidence for wavefunctions 
as opposed to electron density.

I wonder if anyone has any views on this and/or whether they might 
provide examples of this kind of work.

eric scerri
>>>>>>>>>>>

  I suppose you were saying phase information can be recovered from
measurement of electron distribution according to some reports. 

  Mathematically the phase information of the molecular orbitals
in a wavefunction is removed in its transformation to a electron
probability density function. 
Two functions of electron density for the interpretation of 
molecular structure and reactivities I know of are the Bader Laplacian and the
one-electron potential. Both functions are capable of prediction of 
such molecular properties as lone-pair locations without any reference to MOs.
But the phase information of the HOMO is missing
in the Laplacian (a point noted in Bader's book) and the
one-electron potential.  So you still have to turn to the MO
theory for the interpretation and prediction of systems such as
pericyclic reactions.  

  There are other approaches to description of chemical 
reactivities like Fukui functions and Politzer's local ionization 
function that might recover other properties in the electron 
density. 

  On a related note I recall that a few weeks ago you were asking
for suggestions of material on philosophical treatise of density 
functional theory. A perhaps useful paper for your purpose I can think
 of is the one by Richard Bader published about 3 years ago in the 
international journal of quantum chemistry. It has a title 
like "the short-sighted nature of DFT theory". The exact title could
differ from it quite a bit. 

Wai-To Chan