Resolution of the Band Gap Prediction Problem for Materials Design.

An important property with any new material is the band gap. Standard density functional theory methods grossly underestimate band gaps. This is known as the band gap problem.

Accurate Ab Initio Quantum Mechanics Simulations of Bi2Se3 and Bi2Te3 Topological Insulator Surfaces.

It has been established experimentally that Bi2Te3 and Bi2Se3 are topological insulators, with zero band gap surface states exhibiting linear dispersion at the Fermi energy. Standard density functional theory (DFT) methods such as PBE lead to large errors in the band gaps for such strongly correlated systems, while more accurate GW methods are too expensive computationally to apply to the thin films studied experimentally. We show here that the hybrid B3PW91 density functional yields GW-quality results for these systems at a computational cost comparable to PBE.

The magnetic and electronic structure of vanadyl pyrophosphate from density functional theory.

We have studied the magnetic structure of the high symmetry vanadyl pyrophosphate ((VO)(2)P(2)O(7), VOPO), focusing on the spin exchange couplings, using density functional theory (B3LYP) with the full three-dimensional periodicity. VOPO involves four distinct spin couplings: two larger couplings exist along the chain direction (a-axis), which we predict to be antiferromagnetic, J(OPO) = -156.8 K and J(O) = -68.

Silicon nanowires as efficient thermoelectric materials.

Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT-a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another.