Professor Bellaiche's primary interests are the prediction, design and optimization of properties of semiconductors and ferroelectric materials. He uses state-of-the-art electronic-structure methods to study electronic, structural, optical, dielectric and piezoelectric properties.

Electronic-structure methods provide a powerful set of tools for the design and prediction of material properties. At least two different methods corresponding to two different system sizes are technically distinguishable: first-principles calculations vs. second-principles approaches. First-principles calculations can be used to investigate systems of normal size (up to 100 atoms) with few-percent accuracy, using only the atomic numbers of the atoms and some initial guess of the atomic coordinates as input. On the other hand, "second-principles" approaches have been recently developed to extend the reach of first-principles calculations by investigating properties of large systems (100 - 1 million atoms). Our interests are in applying these two electronic-structure techniques to study properties of technologically important materials.

More precisely, our current research program is divided into three activities:

• Ferroelectric systems. A particular project is to design compounds with optimum or new structural, piezoelectric and dielectric properties.

• Semiconductor compounds. This includes surface and alloying effects on structural, optical, and electronic properties. In particular, our focus is on the microscopic understanding of opto-electronic materials (III-V and II-VI semiconductors) and blue-laser systems (wide-band gap nitrides).

• High-Pressure Physics. Emphasis is placed on pretransitional effects, i.e., on effects occurring in a crystallographic structure just before it undergoes a phase transition to another structure. In particular, we would like to know what detailed mechanisms are associated with these pretransitional effects.

Modern computational and simulation methods can provide the fundamental understanding needed for progress in applied fields such as semiconductor technology, piezoelectric devices, and material science. As a result, significant advances in the design and the optimization of properties of complex systems can now be achieved.