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Explanation of the London Dispersion Force

Can anyone give me a brief overview of what's actually going on in an intermolecular attraction between particles that possess no permanent dipole? As far as I can see the 'classical' explanation (involving transient dipoles) is, from a quantum mechanical point of view, ridiculous. No urgency to this one, it's just been playing on my mind.

Reply 1

EierVonSatan

eek, agreed the traditional 'hand-wavey' explanation does seem to defy a quantum mechanical treatment, but so does organic mechanisms since two electrons clearly don't move together to attack things. The dispersion force is in fact a quantum mechanical outcome of intermolecular interactions, it has something to do with pertubation theory of the coulomb interactions between the two atoms/molecules and apparently has nothing to do with instantaneous dipoles :biggrin:

Reply 2

-Kav-

Aye, I think that's about the best any of us here is going to do. I think I'll have to hunt down a suitable textbook or my computational chemistry genius of a professor to get anything more rigorous. Cheers for confirming that I'm on the right lines, though, as I was starting to think that I was imagining a problem that wasn't there. :p:

I've always forgiven mechanistic organic stuff on the ground that it's so predictively useful. In this case, the idea of instantaneous dipoles has the feel of an out-and-out lie. If the perturbation theory around it is similar to Hartree-Fock, even it'll struggle as an actual explanation, since it's a semi-classical model in itself.