RICERCA ITALIANA     

Understanding ab-initio the structural, electronic and optical properties of nanostructured and low-dimensional semiconductor systems

Università degli Studi di Modena e Reggio Emilia

Abstract

This project is aimed to integrate and develop the research capabilities of four teams having complementary expertises in the study of processes related to the electronic and optical properties of nanostructured and low-dimensional semiconductor systems. Such processes, which are very important both from the point of view of fundamental science and that of technological applications, will be studied at the atomic level, exploiting the now powerful combination of quantum-mechanical theory and computer simulation.

The theoretical understanding of the electronic states is a fundamental step for the design of new materials, being intimately linked with their experimental characterization. Many experimental quantities, obtained as the response to external probes in modern nondestructive spectroscopies, as photoemission, energy-loss, or optical absorption spectra, involve electronic excitations, and hence require a detailed knowledge of electronic excited states. It is, thus, critical to be able to describe accurately the latter with reliable and efficient theoretical approaches.

In order to reach our goals we will coordinate and combine the activities of four research groups. The latter are, since long time, active in this research field along timely and relevant lines, documented by the amount of high-profile publications. Besides being now among the world leading groups in the field, they have also demonstrated a strong availability and ability >>>

Principal Investigator

Stefano OSSICINI Università degli Studi di MODENA e REGGIO EMILIA

Research Objectives

The scientific aim of this research program is the substantial improvement and development of a theoretical approach "with atomic understanding" for the determination of the structural, electronic and optical properties of nanostructured and low-dimensional semiconductor systems.

To reach this goal this program will integrate and develop the research capabilities of four research teams in the field of the fundamental science of nanoscale systems and advanced materials. These teams have actively and succesfully collaborated in the past in several projects, such as the PRIN Ossicini 1997, PRIN Ossicini 2002, the CNR Project MADESS2, and the INFM-PRA Project RAMSES 2000 and the INFM-PAIS Project CELEX 2002. Moreover both Roma and Milano nodes already belong to an European Network of Excellence (NoE) entitled NANOQUANTA, whereas Modena and Napoli nodes are both active in the European Network Psi-k "Electronic Structure Calculation of Solids and Surfaces"; besides Ossicini is the European Coordinator of the submitted NoE Project "Silicon Nanophotonics".

Through the active collaboration and the powerful combination of quantum-mechanical theory and computer simulation we will make contact with nanoscience experimental studies and directly with technologically relevant structural, electronic and optical processes. Several state-of-the-art computer codes are available for the proposed research program: besides publicly available codes such as >>>

Timescale

24 months

National and international background

Understanding and controlling the properties of materials is crucial for improving the information technology on which our modern life is built. In particular, the ability to describe the electronic excitations with accurate ab-initio methods is of fundamental importance for the study of new materials. The theory plays a crucial role, not only from the point of view of the fundamental research, but also because a precise knowledge of the electronic excitations represents a fundamental step towards the innovation, design and fabrication of materials and devices based on nanoscale-technology having properties tuned to the requirements of real technological applications.
Although Density Functional Theory (DFT) [1] has proven to be a powerful tool for calculating electronic ground-state properties, it is of limited use for providing an accurate description of spectroscopic properties. For instance, it is well known that DFT underestimates the energy gaps, and only by overcoming the single particle approach [2] it is possible to obtain good agreement with the experimental data.



Fig. 1 Experimental gaps (dashed) compared with theoretical DFT-LDA ones (circles) and those within the GW method (squares) [3].

Thus DFT should be considered as a first step towards more sophisticated theoretical and computational schemes based on many-body perturbation theory (MBPT) or, alternatively, on time-dependent density-functional >>>