My group is engaged in research in condensed matter theory covering the areas of semiconductors, metals, surfaces, defects, nanostructure materials (such as fullerenes, nanotubes, and clusters), and many-electron effects in solids. The objective is to explain and predict the properties of materials using first-principles theories and computations.
Current Research Projects
A major interest of my group is nanoscience, in particular, systems involving nanotubes. Nanotubes are tubular structures, typically several nanometers in diameter and microns in length. These quasi-1D materials have novel properties (e.g., chiral currents and quantized conductance) of fundamental and practical interest. Systems being studied include defects on nanotubes, nanotube junctions, and nanopeapods. Various structures consisting of assembly of nanotubes and other nano-objects such as fullerenes and clusters are also being investigated.
The properties of a solid are dictated by the interacting electrons and ions in the system. Many properties are strongly affected by electron correlation effects. We are developing many-body perturbation methods and quantum Monte Carlo methods for studying these effects in real materials. In particular, first-principles one-particle and two-particle Green’s function approaches are used to compute quasiparticle energies and optical spectra for interpreting spectroscopic data and to predict phenomena such as photo-induced transformations. Quantum Monte Carlo techniques are used to determine ground-state properties of correlated electron systems. Many-electron effects (e.g., electron-hole interaction in optical processes) are particularly dominant in reduced dimensional systems such as surfaces, polymers, and clusters.
Nuclear magnetic resonance (NMR) is an important tool for studying the chemical, electronic and structural properties of liquids and solids. We have developed a method which allows the ab initio calculation of NMR chemical shifts in extended systems. This approach is applied to investigate crystals, amorphous solids, and liquids.
Hardness is a macroscopic property that is far from well understood. We are investigating the limits of the mechanical strength of solids, with the goals of understanding the physical origins of hardness and predicting new hard materials.
In the News
Researchers at Lawrence Berkeley National Laboratory and the University of California, Berkeley, have developed a new precision approach for synthesizing graphene nanoribbons from pre-designed molecular building blocks. Using this process the researchers have built nanoribbons that have enhanced properties—such as position-dependent, tunable bandgaps—that are potentially very useful for next-generation electronic circuitry.
Launched as a pilot project at Berkeley Lab, the Cleantech to Market program is finishing its first semester as an official class at UC Berkeley's Haas School of Business, and it's safe to say the students learned more than they expected on how to take a technology from the laboratory to the marketplace. What was less expected is how much the scientists got out of the program.