Reddit mentions of The Jahn-Teller Effect

My dissertation is on the pseudo Jahn-Teller effect (symmetry breaking in highly symmetric, NON-electronically degenerate systems) and developing a DFT method for assessing vibronic coupling. This is probably one of the best explanations I've heard from a non-theory person.

>This is because most molecules don't have low-lying electronic states with the "right" symmetry to see the coupling.

There's a pretty straightforward rule that you can use to predict which electronic states are valid for vibronic coupling. The direct product of the electronic state of State #1 and State #2 must yield the symmetry of the vibrational mode causing the symmetry breaking.

So, a simple example is Si2H4 (Ethylene with the carbons replaced with silicon). The molecule is planar (D2H symmetry) but unlike Ethylene, Si2H4 likes to take on a trans-bent configuration (C2H symmetry). The vibrational mode responsible for this is a b2G mode. Si2H4 is in a 1AG state, so we need to look for excited states that will give b2G when a direct product is taken... So you go and look at a product table for D2H (http://www.webqc.org/symmetrypointgroup-d2h.html at the bottom) you can see the only combination using 1AG that gives B2G is B2G... So the Jahn-Teller problem is described as: 1AG x B2G -> B2G.

I use this reference to teach JT-effect in an undergrad quantum lab.

This book was written by arguablythe expert on this stuff. You can search for more work by Isaac Bersuker, James Boggs, and Alexander Boldyrev if you're interested.

Sorry I suck at reddit formatting.