David Farrell

Research Interests

My research interests include:

• • Multiple time and length-scale simulation methods

  • Continuum and discrete modeling methods (Finite elements, ab initio and classical molecular dynamics/statics)

  • Reaction mechanisms and kinetics in hydrides

  • Radiation damage and fracture in ceramics

Current Research

General adoption of hydrogen as a vehicular fuel depends on the ability to store hydrogen on-board at high volumetric and gravimetric densities, as well as the ability to extract it at rapid rates. Recent experimental and theoretical studies have identified several new complex hydrides with thermodynamic properties and material storage capacities approaching and, in some cases, surpassing the targets set by the U.S. Department of Energy. However, these materials are known to suffer from extremely poor hydrogen absorption and desorption kinetics. To determine the source of the poor kinetics, we will use ab-initio molecular dynamics (AIMD) to understand the microscopic kinetic processes involved in hydrogen release, research which has been funded by the DOE (DE-FG02-07ER46433) and the NSF (CBET- 0730929). We have also begun work to examine the phase diagrams for mixed complex hydride systems

(LiNH₂-LiBH₄, for example), and point defect formation and migration.

Our calculations will provide an in-depth atomistic picture of the chemical reactions and diffusion pathways controlling the kinetics of hydrogen release in some of these new complex hydrides. To fully explore these systems will require many calculations with hundreds of atoms for time periods of up to nanoseconds. However, the predictive power of AIMD comes at a price: to run a system of 150 atoms for 5 picoseconds on 32 2.4 GHz processors requires roughly 5 days; to simulate a system of 300 atoms for 100 picoseconds would take roughly 800 days. Thus, this class of problem becomes intractable on a small cluster. Instead, our calculations are run on supercomputers such as the Argonne National Laboratory Leadership Computing Facility's IBM Blue Gene/P, Intrepid, and the National Institute for Computational Science's Cray XT5, Kraken.

Biography

I am originally from Plattsburgh, NY; in 2003, I received my BS in Mechanical Engineering from Clarkson University in Potsdam, NY. I received my PhD in Mechanical Engineering in 2008 from Northwestern University in Evanston, IL. The focus of my dissertation was the characterization of defect structures in silicon carbide fusion reactor components. During graduate school, I had the opportunity to work at both Sandia National Laboratories campuses and the Naval Research Laboratory.

As a post-doc in the Wolverton group, I have been working on modeling hydrogen release from hydrogen storage materials using molecular dynamics with interatomic interactions described by density functional theory.

Publications

Farrell, D., A. Thompson, D. Shin, C. Wolverton. First-principles molecular dynamics study of the structure and dynamic behavior of liquid Li₄BN₃H₁₀. Phys. Rev. B. 80, 224201 (2009)