Berkeley Lab - Scientific Computing Seminar

Date:

Wednesday, April 23, 2008

Time:

11:15am-12:15pm

Location:

Building 50F, 1647 Conference Room

Seminar Speaker:

Burcin Temel
Department of Chemical Engineering, University of California - Berkeley

Title:

Scattering and Kinetics of Surface Reactions

Abstract:

In the first part of my talk, I will present Minimum Error Method (MEM), a least-squares minimization method used with preconditioned conjugate gradient, which provides an efficient and accurate alternative to solve systems of ordinary differential equations. Existing methods usually utilize matrix methods, which are computationally expensive. MEM, which is based on the Chebyshev polynomials as a basis set, uses the recursion relationships and fast Chebyshev transforms which scale as O(N). For large basis set calculations this provides an enormous computational efficiency in the calculations. Chebyshev polynomials are also able to represent non-periodic problems very accurately. We applied MEM on elastic and inelastic scattering problems: it is more efficient and accurate than traditionally used Kohn variational principle, and it also provides the wave function in the interaction region.

The second part of my talk is on a phenomenological kinetics (micro-kinetic modeling) vs. kinetic Monte Carlo study for CO oxidation on RuO₂ surface. Phenomenological kinetics (PK) is widely used in industry to predict the optimum conditions for a chemical reaction. PK neglects the fluctuations, assumes no lateral interactions, and considers an ideal mix of reactants. The rate equations are tested by fitting the rate constants to the results of the experiments. Unfortunately, there are numerous examples where a fitted mechanism was later shown to be erroneous. We have undertaken a thorough comparison between the phenomenological equations and the results of a kinetic Monte Carlo (kMC) simulations performed on the same system. We showed that the PK equations are qualitatively consistent with the kMC results but are quantitatively erroneous as a result of interplays between the adsorption and desorption events.

Sponsor of Seminar:

Lin-Wang Wang

Scientific Computing

Contact Esmond G. Ng EGNg@lbl.gov