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SUMMARY:Quantum topological effects in the transport properties of ionic c
 onductors - Professor Stefano Baroni\, SISSA — Scuola Internazionale Sup
 eriore di Sudi Avanzati\, Trieste
DTSTART:20200212T141500Z
DTEND:20200212T151500Z
UID:TALK135736@talks.cam.ac.uk
CONTACT:Lisa Masters
DESCRIPTION:According to the Green-Kubo theory of linear response\, the el
 ectric conductivity of an extended system is proportional to the time inte
 gral of the equilibrium current auto-correlation function. In this talk I 
 will provide an answer to the following silly question: how is it that in 
 ionic insulators a vanishing conductivity results from a non vanishing cur
 rent? The answer is rooted in the topological quantisation of adiabatic pa
 rticle transport\, a property discovered by Thouless in the early eighties
 . Thouless’ theory allows one to give a rigorous definition of the atomi
 c oxidation states in extended systems\, a concept that\, despite its ubiq
 uitousness in chemistry\, has long eluded a proper quantum mechanical inte
 rpretation. By combining this theory with a gauge invariance principle\, r
 ecently introduced in the theory of heat transport\, I will demonstrate th
 at the substitution of the real-valued\, time-dependent\, Born effective-c
 harge tensors that enter the quantum-mechanical definition of the ionic cu
 rrent with integer-valued\, time-independent\, scalar oxidation numbers re
 sults in the same electric conductivity\, as predicted by the Green-Kubo t
 heory. A few numerical experiments on molten salts will be reported on\, d
 emonstrating the soundness of our findings. These findings not only provid
 e an answer to the silly question\, but also relieve us from the burden of
  computing Born effective charges on the fly in ab-initio molecular-dynami
 cs simulations of charge transport in ionic conductors.
LOCATION:Department of Chemistry\, Cambridge\,  Pfizer Lecture Theatre
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