CCL: RE: Orbitals

 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
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