London dispersion force

[Gavroy]

hi,
lately i am concerned with Van der Waals forces and I often found in chemistry books the so-called London dispersion force, which says that the potential energy of the Van der Waals interaction is:

U=-2/3 a1a2I1I2/(r^6*(I1+I2)

but by now I could not find a theoretical derivation of this approximation?

does anybody know one in the internet?

[Bill_K]

You'll probably get better results asking this on the Atoms & Molecules forum

[alxm]

To begin with there's London's original papers:
Eisenschitz and London, Z. Physik 60, 491 (1930), London, Z. Physik 63, 245 (1930)

They're also available in (a somewhat mediocre) translation in Hettema "Quantum Chemistry, Classic Scientific Papers", if you can find it. There's a somewhat hand-waving derivation in Landau-Lifshitz volume 3, §89. Also in Atkins and Friedman's "Molecular quantum mechanics" section 12.5 (3rd edition).

I found an online account in some lecture notes here (http://www.soton.ac.uk/~compchem/other/perturbation_theory.pdf), page 32-34. It's the same derivation as used in all the above.

[Gavroy]

ah, this is exactly what i was looking for, thank you