Subject: CCL: RE: Orbitals

From: "Leif Laaksonen" <leif.laaksonen_at_csc.fi>
Date: Wed, 28 May 2003 21:24:41 +0300

Hi,

I might remember wrong from my primary courses in quantum chemistry
that only obsrvables are the expectation values from the wave
function!

This means that while the wave function (|P>) as such is not
observable the expectation value of property X is (<P|X|P>).

Regards,

-leif  

-----Original Message-----
From: Computational Chemistry List [mailto:chemistry-request_at_ccl.net] On Behalf Of Guosheng Wu
Sent: Wednesday, May 28, 2003 7:46 PM
To: chemistry_at_ccl.net
Subject: CCL:Orbitals

> > > --- elewars <elewars_at_trentu.ca> wrote:
> > > > 2003 May 28
> > > >
> > > > Are MOs physically real? This is a meaningful question only if there is some
> > > > experiment or observation that could provide an answer _yes_ or _no_.  Is there,
> > > > at least in principle, such an experiment or observation?

> > Guosheng Wu wrote:
> > 
> > > MO is just a useful mathematical tool for quantum chemistry/physics, and
> > > it seems to me itself does not have much physical meaning.
> > >
> > > However, many properties from MOs are meaningful and can be observed
> > > by exmperiments: such as the square of absolute MOs (|MO|^2) corresponding
> > > to the electronic density. Things like |MO|^2 of d-orbitals were published
> > > in a Science article last one or a few years.

> --- elewars <elewars_at_trentu.ca> wrote:
> > Hello,
> > 
> > Thanks for your ideas. If photoel. spectra (and Koopmans theorem--in this case the
> > second MO is at the ionization limit) really measure the energy difference of two MOs,
> > then MOs exist!
> > 
> > In any case, it is an interesting discussion.
> > 
> > EL
> > =====

The properties from |MO|^2 exist does not really mean MO exists.
 
When we know some properties from x^2 exist and can be measured,
this does not mean x exists and can be measured.
 
For example, what does the complex number(i) mean in the real world?
Measurable? Not really, but obviously it's a useful mathematical tool
for lots of applications. Certainly (i^2=-1) means something. Right?

Related issue for absolute energy: energy difference is measurable 
by many kind of experiments, but not for the absolute energy. 
 
This may lead to some kind of philosophical problem, if one has 
such a taste.

Guosheng

__________________________________
Do you Yahoo!?
Yahoo! Calendar - Free online calendar with sync to Outlook(TM).
http://calendar.yahoo.com

-= This is automatically added to each message by mailing script =-
To send e-mail to subscribers of CCL put the string CCL: on your Subject: line
and send your message to:  CHEMISTRY_at_ccl.net

Send your subscription/unsubscription requests to: CHEMISTRY-REQUEST_at_ccl.net 
HOME Page: http://www.ccl.net   | Jobs Page: http://www.ccl.net/jobs 

If your mail is bouncing from CCL.NET domain send it to the maintainer:
Jan Labanowski,  jkl_at_ccl.net (read about it on CCL Home Page)
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+