ELFT HÍRADÓ

[tcsaba <tcsaba AT eik.bme.hu>]

                     M E G H Í V Ó - I N V I T A T I O N

      Seminar Series of the Department of Theoretical Physics at the
            Budapest University of Technology and Economics


                             Jenő Kürti
              (Department of Physics of Complex Systems,
                     Eötvös Lóránd University)

            Bond length alternation in hydrocarbon rings


Bond length alternation (BLA) is an inherent trait of linear polyenes. 
For
finite chains this is simple the consequence of chain end effects.
Although decreasing with increasing chain length, BLA retains for 
infinite
long chains – this is the well known Peierls distortion.
The question is what happens for cyclic hydrocarbons: the annulene
molecules. In the antiaromatic case (nC=4n) the existence of the BLA is 
a
triviality due to the Jahn–Teller effect. The situation is much more
subtle for aromatic (nC=4n+2) rings. The best known example is benzene,
where there is no BLA.
We demonstrate theoretically, using both the Longuet-Higgins–Salem (LHS)
model and density functional theory that increasing the number of carbon
atoms in the aromatic rings leads to the appearance of the BLA for large
enough rings. The reason for this is the pseudo Jahn–Teller effect. In 
the
infinite limit the aromatic and the antiaromatic rings (as well as the
linear chains) behave similarly, showing Peierls distortion.


Idöpont: 2016. március 18. péntek, 10:15
Helyszín: BME Fizikai Intézet, Elméleti Fizika Tanszék,
Budafoki út 8. F-épület, III lépcsöház, szemináriumi szoba