ALCF Science 1 - Argonne National Laboratory

argonne leadership computing facility
Materials Science
Probing the Non-scalable Nano Regime in Catalytic Nanoparticles
with Electronic Structure Calculations
To get insight into quantum-size effects (QSE) of nano-clusters and
estimate the impact on their catalytic ability, Argonne researchers,
in collaboration with colleagues at the Technical University of
Denmark, performed Density Functional Theory (DFT) calculations
on cuboctahedral gold clusters with adsorbed oxygen and carbon
monoxide. The effective cluster sizes ranged from 0.5 to about 4 nm
(13 to 1,415 atoms). The calculations were done on the IBM Blue
Gene/P supercomputer at the Argonne Leadership Computing Facility.
The researchers found the QSE to be energetically converged for
clusters larger than 309 atoms – where they obtained the adsorption
characteristics of single crystal surfaces. The QSE effects were on
the order of 1 eV and had a huge impact on the estimated catalytic
properties of the clusters. They also found the QSE to be essentially
reproduced by a simple, tight-binding model with nearest-neighbor
matrix elements estimated from bulk-gold calculations and fit to
reproduce the adsorption characteristic of the single-crystal surfaces.
INCITE Allocation:
10 Million Hours
“The computational resources
available through the INCITE
program have permitted us to
analyze the catalytic and electronic
properties of nanoparticles that
would have been impossible
to study on more conventional
systems.”
INCITE PROGRAM
Research accomplishments include:
Completed parallelization of dense linear algebra—can now always
run in VN mode with state-parallelization and will never run out of
memory;
Found new, efficient BG/P mappings;
Did additional general tuning of the parallel performance and are
working more closely with IBM to optimize the code further;
Discovered a scheme that corrects for numerical grid effects
(egg-box effect), which can sum up to several eVs for large
systems – and which furthermore influence the relaxation
of clusters (grid-snapping to hotspots of the egg-box
effect).
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Currently, the researchers are pursuing geometric
relaxation of larger clusters and focusing their efforts
on Pt and Rh, which, contrary to Au, have a partially
filled d-band. They continue to work on integrating
the HDF5 library into GPAW to allow the efficient
restart of calculations using wave functions. They’re
also addressing a thorny technical challenge: Dense
diagonalization arising from ScaLAPACK is one of several
Amdahl limitations in the canonical O(N3) DFT algorithm.
This is a non-trivial algorithmic bottleneck that will likely require
implementing O(N) DFT algorithms as a resolution.
Electron density perturbation from carbon monoxide adsorption
on a multi-hundred atom gold nanoparticle. The perturbation causes
significant quantum size effects in CO catalysis on gold particles.
Contact Jeff Greeley
Argonne National Laboratory | jgreeley@anl.gov