Bulletin of the American Physical Society
2007 APS Four Corners Section/SPS Zone 16 Joint Fall Meeting
Volume 52, Number 14
Friday–Saturday, October 19–20, 2007; Flagstaff, Arizona
Session J2: Condensed Matter: First Principles Calculations |
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Chair: Mark Riffe, Utah State University Room: Chemistry (Bldg. 20) Room 225 |
Saturday, October 20, 2007 11:00AM - 11:36AM |
J2.00001: Recent Developments in Electronic Structure Methods: The Quasiparticle Self-Consistent GW Approximation Invited Speaker: The ability to solve the fundamental equation of motion of condensed matter --- the Schrodinger equation---from first principles, has evolved a great deal in the last 30 years. The standard workhorse, the Local Density Approximation (LDA) is now widely used in most branches of science and engineering. However, it has many limitations, and numerous attempts to extend and improve on the the LDA have been attempted. There have been notable successes, but most of these methods are semi-empirical, and tend to be specialized --- suitable for resolving one or another failing of the LDA. Here we prsent a new type of approach based on Hedin's GW approximation. This approach, which we call the quasiparticle self-consistent $GW$ (QS$GW$) approximation, is based on a kind of self-consistent perturbation theory, where the self-consistency is constructed to minimize the perturbation. QS$GW$ describes optical properties in a wide range of materials rather well, including cases where the local-density and LDA-based $GW$ approximations fail qualitatively. Self-consistency dramatically improves agreement with experiment, and is sometimes essential. QS$GW$ avoids some formal and practical problems encountered in conventional self-consistent $GW$, which will be discussed. QS$GW$ handles both itinerant and correlated electrons on an equal footing, in a true \emph{ab initio} manner without any ambiguity about how a localized state is defined, or how double-counting terms should be subtracted. Weakly correlated materials such as Na and $sp$ semiconductors are described with uniformly high accuracy. Discrepancies with experiment are small and systematic, and can be explained in terms of the approximations made. Its consistently high accuracy make QS$GW$ a versatile method that can reliably predict critical energy band properties of GaAs, CuInSe$_2$, TiO$_2$ and NiO in a unified framework. [Preview Abstract] |
Saturday, October 20, 2007 11:36AM - 11:48AM |
J2.00002: Ab Initio Study of Covalent Functionalization of Defective Carbon Nanotubes by Carboxyl Group Nabil Al-Aqtash, Igor Vasiliev Covalent sidewall functionalization of carbon nanotubes with carboxyl groups (COOH) is investigated using first principles computational methods. The binding energies and equilibrium geometries of functionalized nanotubes with no surface defects, Stone-Wales defects and vacancies are calculated in the framework of density functional theory combined with the generalized gradient approximation. Our calculations show that the binding of COOH groups with carbon nanotubes containing surface defects is stronger than that with defect-free nanotubes. Furthermore, the presence of COOH groups on the surface leads to a considerable change of the electronic and structural properties of defective nanotubes. Our results suggest that surface defects play an important role in the formation of chemical bonds between carboxyl groups and carbon nanotubes. [Preview Abstract] |
Saturday, October 20, 2007 11:48AM - 12:24PM |
J2.00003: Polar oxide interfaces: Understanding the technology of the future using first-principles calculations Invited Speaker: Perovskite oxides are a class of materials that display a spectacular array of physical phenomena including magnetism, ferroelectricity, piezoelectricity, and superconductivity. Incorporating such phenomena into existing semiconductor technology is one of the grand challenges of our century. However, achieving this goal has both practical and fundamental obstacles. In this talk, two polar oxide interfaces are discussed: the interface between Si/SrTiO$_3$ and SrTiO$_3$/LaAlO$_3$. First-principles electronic structure calculations are used to understand the practical challenge of growing SrTiO$_3$ on Si, and to explain the novel, highly-mobile electron gas that forms at the interface between SrTiO$_3$ and LaAlO$_3$. [Preview Abstract] |
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