| Topic: |
Science > Physics |
| User: |
"Dr Photon" |
| Date: |
26 Aug 2005 11:36:02 AM |
| Object: |
Bohrn again |
Is there life in the old Bohr yet?
Quoting from
http://www.nature.com/nphys/journal/vaop/nprelaunch/full/nphys115.html
"A look back at Bohr's molecular model offers a fresh perspective on
the formation of chemical bonds between atoms in hydrogen and other
molecules.
Although it is possible to model the electronic structure of molecules
with great accuracy, such numerical methods provide little intuitive
insight into electron-electron interactions. In two papers, in
Physical Review Letters and Proceedings of the National Academy of
Sciences, Anatoly Svidzinsky and colleagues [1,2] have taken a trip
down memory lane to uncover an intriguing approach to understanding the
chemical bonds within molecules, and at the same time take a fresh
perspective on the "old quantum theory" developed by Niels Bohr in
1913.
The famous Bohr model introduced the quantized nature of electron
orbits in one-electron atoms, long before wave mechanics was developed.
Much later, in the 1980s, the so-called D-scale approach provided a
quantitative description of the two electrons surrounding a helium
nucleus, by generalizing the Schr=F6dinger equation to D dimensions; the
situation relevant to the three-dimensional world is deduced by
interpolating between the D =3D 1 and the D =3D infinity limits.
However, neither approach - although each successful in its own realm
- has so far yielded satisfactory results for two-centre problems,
such as the hydrogen molecule. Svidzinsky et al. have re-examined the
D-scale approach and show how a simple modification can fix its
shortcomings [1]. Whereas the original did not even predict a bound
ground state for the hydrogen molecule, their new version provides
quantitative values that are remarkably close to those obtained from
extensive computer simulations. Furthermore, the authors show that, in
the large-D limit, dimensional scaling can reproduce the Bohr model -
notably by bringing in quantum mechanical concepts that were completely
unknown to Bohr at the time.
Svidzinsky et al. explore further [2] this link between 'new' and
'old', to demonstrate that Bohr's planetary model is indeed able to
quantitatively describe the hydrogen molecule and some more complicated
molecules such as diatomic lithium - and gives a clear physical
picture of how a chemical bond forms. "
[1]http://link.aps.org/abstract/PRL/v95/e080401
[2]http://www.pnas.org/cgi/content/abstract/102/34/11985
Note to cranks: while the Bohr model has many obvious successes, and
from the above article these are still being extended, still nobody's
going to ditch the current model in favour of it.
It's a hard life.
br
.
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