Berkeley Lab - Scientific Computing Seminar

Date:

Friday, May 30, 2008

Time:

1:00pm-2:00pm

Location:

Building 50F, 1647 Conference Room

Seminar Speaker:

David Prendergast
Theory Facility, Molecular Foundry
Lawrence Berkeley National Laboratory

Title:

Computational Spectroscopy at the Molecular Foundry

Abstract:

Providing reliable and predictive models for novel nanoscale systems is one of the goals of the Theory Facility at the Molecular Foundry. To this end we are developing several computational methodologies which provide in silico spectroscopy. In particular, we use first principles methods to simulate excited state properties of various materials over a wide energy scale: from meV vibrational scattering to UV/Visible valence excitations to X-ray core-level spectroscopy. Within the realm of density functional theory (DFT) one can accurately describe x-ray excitations with careful consideration of the physics of the excited states. Examples will be presented for solid state, liquid, and molecular systems. Computational efficiency can be greatly improved through the construction of compact Hamiltonians which accurately reproduce ab initio electronic energy levels, proving advantageous in providing numerical convergence of spectroscopic simulations. Standard ground state DFT methods have well-known shortcomings in describing systems in valence excited states - most famously band gap underestimation and neglect of excitonic effects. Various approaches are outlined that overcome these issues by using beyond-DFT methods such as the GW approximation and the Bethe-Salpeter equation. Applications to the excitonic states of carbon nanotubes will be presented.

Sponsor of Seminar:

Lin-Wang Wang

Scientific Computing

Contact Esmond G. Ng EGNg@lbl.gov