Theory of the Electronic Properties of Solids Prof. Alfonso Baldereschi, Full Professor Prof. Raffaele Resta, Full Professor Prof. Maria Peressi, Associate Professor Dr Alberto Debernardi, Postdoctoral Fellow (INFM) Dr Agnese Callegari, Postdoctoral Fellow (INFM-DEMOCRITOS) Dr X.M. Duan, Postdoctoral Fellow Dr A Stroppa, PhD student Dr Michele Tosolini, Research Fellow The research activity is devoted to the theoretical/computational study of structural, electronic, magnetic and optical properties of solids and in particular of semiconductors and insulators. The main research fields are: Semiconductor epitaxial heterostructures. Computational study based on density functional theory in the local density approximation and with the pseudopotential method. In particular: heterojunctions between wide-gap semiconductors, with the investigation of the relationship between interface morphology and stability and electronic properties of the junction (e.g. ZnMgSe/ZnCdSe); in particular, role of the atomic interdiffusion at the interface on the existence of localized electronic states in case of heterovalent heterojunctions (ZnSe/Ge); heterojunctions between alloys, and variation of the band alignments with composition and local compositional fluctuations; heterojunctions between crystalline Si and amorphous Si, with and without H (and with different content); structural and electronic properties of cross-sectional (110) surfaces of various defected GaAs samples with different defects (vacancies; impurities such as Si, N, In; complex defects); simulation of scanning tunnelling microscopy images. Dielectric polarization in solids. Study of macroscopic polarization with the use of the Berry phase method, developed by R.Resta (starting from 1992). Study of microscopic polarization by developing novel approaches, based on linear-response theory. Further development of the theory of the insulating state, based on the localization of the electronic wavefunction, and related to the Berry phase. Materials of interests are semiconductors, ferroelectric oxides, and also quasi-one-dimensional systems (polymers, nanotubes). Magnetic materials. Structural, electronic and magnetic properties of MnAs compound in different strain configurations and magnetic phases, in the local spin density approximation. Properties of Mn doped Si(x)Ge(1-x) alloys, and characterization of their magnetic properties (halfmetallicity, in particular) with respect to the alloy composition and local environment around the magnetic impurities. Interfaces between conventional semiconductors and magnetic materials, in particular MnAs and Heusler alloys. Wide gap semiconductor alloys. Alloys based on (Ga,In)(As,N) are studied with supercell approach, with particular attention to the local atomic type distribution and electronic and optical structure.

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