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Abstract :
[en] The present work is devoted to an ab-initio characterization, using planewave and localized basis sets, of multiferroic and magnetoelectric materials. After a general description of the underlying concepts and computational techniques, we focus on BiFeO3, which is probably the most intensively studied multiferroic.
We start our investigation by comparing the ability of different exchange-correlation functionals
(LSDA(+U), GGA and hybrid) to accurately describe the most fundamental properties of BiFeO3
(crystallographic structure, electronic band structure, magnetism, phonons at Gamma, Born effective charges). Next we present infrared reflectivity and Raman spectra obtained from first-principles and compare them to experimental data.
We then extend the study of the dynamical properties of BiFeO3 to the whole Brillouin zone by
analyzing the phonon band structure, density of states and interatomic force constants. We also
use combined Einstein and Debye models to fit the specific heat as obtained from first-principles
and compare it to experimental data. The final part of this thesis is devoted to the investigation
of pressure driven spin phase transitions in Bi2FeCrO6 .
