DF Seminar

[Rosita Glavina]

Department of Physics - University of Trieste

Thursday 25 February 2010 - 3.00 pm
Room 204 (2nd floor LB)

prof. Raffaele Resta
(University of Trieste)

TITLE:
HOW A SERIES OF COMPUTATIONS CHANGED OUR VIEW OF THE POLARIZATION OF SOLIDS

ABSTRACT:
The concept of macroscopic polarization is the basic one in the
electrostatics of dielectric media: but for many years this concept has
evaded even a precise microscopic definition, and has severely
challenged quantum-mechanical calculations.
Textbooks usually visualize a polarized dielectric as an assembly of
discrete microscopic polarization elements, a la Clausius-Mossotti.
Unfortunately, the electronic distribution inside a real material is
continuous, and often quite delocalized: in such a case, there is no
unambiguous way of defining the macroscopic polarization as a
property of the periodic charge of the polarized dielectric, contrary to
what most textbooks (e.g. Kittel, Ashcroft-Mermin) incorrectly state.
Owing to a series of computer experiments, the concept itself of
dielectric polarization in condensed matter has undergone a change of
paradigm, culminating in the so called "modern theory of polarization"
(based on a Berry phase) in the early 1990s. Before it, it was impossible
to address from a quantum-mechanical viewpoint e.g. the spontaneous
polarization of ferroelectric materials (experimentally known since half a
century and more).
In this talk, I will review the historical developments. Computation after
computation, it became clear what polarization really is and therefore
also how it must be computed. Nowadays, the modern theory is a standard
tool in electronic structure.