Seminars to be announced

[CM ICTP - Trieste]

Joint ICTP/Democritos

INFORMAL SEMINAR on Chemical Physics



Tuesday, 23 October   -    11:00 a.m.


Seminar Room - Main Building   (first floor)



R. CARACAS   ( Ecole Normale Superieure de Lyon )



"Theoretical studies of major earth and planetary materials"


Abstract

We employ first-principles calculations based on the density functional 
theory (DFT) and density-functional perturbation theory (DFPT) to study 
several of the major constituents of the terrestrial and icy planets.
In the first part, we use the latest theoretical developments of the 
DFT and DFPT and their practical implementations in the ABINIT package 
to determine the phase diagram, the compressibility, the high-pressure 
elastic constants and the Raman spectra for (Mg,Fe,Al)(Si,Al)O3 
perovskite and post-perovskite. The elastic constants determined from 
DFPT and from the stress-strain fits differ by only a few GPa, e.g. 
less than 5 GPa for MgSiO3 perovskite, and they fall within 10% of the 
experimental values. The calculations of the Raman spectra are even 
more spectacular, given the extreme requirements for convergence and 
accuracy of dielectric properties, usually hard to obtain. The 
agreement between linear-response and experiment is excellent for both 
peak position and intensity. For example the same three main groups of 
peaks in both theory and experiment characterize the Raman spectra of 
MgSiO3 perovskite. This made us confident of the accuracy of our 
results and we proposed the Raman spectra of the post-perovskite, 
characterized by only one main peak at high pressure. Thus Raman 
spectroscopy can be used as an identification tool for the perovskite 
to post-perovskite phase transition in high-pressure experiments. In 
the same theoretical framework we briefly discuss the pressure 
variation of the Raman spectra of alumina polymorphs.
In the second part we discuss the phase diagram of solid nitrogen. 
Nitrogen phase diagram is characterized by several disordered and 
ordered molecular structures at low pressures and an atomic structure 
at high pressures. Here, we propose a new molecular phase which can be 
a link in the transition path between molecular and atomic nitrogen. We 
also study in detail the dynamical and the spectroscopic properties of 
atomic nitrogen.
=================

	
SEMINAR on  Disorder and strong electron correlations



Thursday, 25 October   -    11:00 a.m.



Seminar Room,  Main Bldg.- first floor


M. VAVILOV  ( University of Wisconsin - Madison )

"Non-linear transport in a two dimensional electron system"


Abstract

	One of the most exciting recent discoveries in condensed matter 
physics is the observation of magnetoresistance oscillations and zero 
resistance states of a two dimensional electron system (2DES).
For a microscopic description of this phenomenon I will introduce a 
quantum kinetic equation for a two-dimensional electron gas.  This 
equation can be used to calculate all transport characteristics of 2DES 
in magnetic fields, including Shubnikov - de Haas oscillations,  smooth 
part of the magnetoresistance, and non-linear electric current in 
response to applied electric fields.  I will describe the components of 
the kinetic equation in terms of a semiclassical picture of electrons 
moving along cyclotron trajectories.  I will apply this equation to 
analyze the current-voltage characteristic of a 2DES, compare 
theoretical predictions with experimental data, and outline potential 
future experiments.