parallel genetic algorithms for the structural characterisation of nanoalloys · 2015-07-06 ·...
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Parallel Genetic Algorithms for the Structural Characterisation of Nanoalloys
Jack Davis School of Chemistry University of Birmingham
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Birmingham Cluster Genetic Algorithm
• The Birmingham Cluster Genetic Algorithm (BCGA) is a genetic algorithm for the structural characterisation of nanoalloys.
• A GA is search method based on the principles of natural selection, sharing key terminology - Generation, Mutation, offspring etc.
• The BCGA includes local minimisation with each step - simplifying the search.
“Stepped Surface”
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Nanoalloys• Metallic nanoparticles
composed of two or more metallic elements.
• Potential optical, electronic and catalytic applications.
• Structural characterisation is an essential step towards understanding these properties.
Core-Shell Multi-Layer
Mixed-Random Janus Mixed-Ordered
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Operations
A + B AB
C
Daven and Ho Crossover
MutationRandom new geometry
SAtom Swap D Displace
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BCGA-DFT• Local minimisation carried
out directly at the density functional theory level.
• Allows the BCGA to capture size-specific effects commonly seen in small clusters, otherwise missed with potentials.
• Hugely expensive, only possibly for 10 atom or less sized clusters.
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Parallelisation• How can we study larger
clusters?
• The BCGA is intrinsically parallelisable as local minimisations have no interdependence.
• Direct MPI parallisation is not possible. We would not be able run DFT codes in parallel alongside the GA.
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Database Method• Pool GA methodology
insures efficiency within a parallel scheme.
• The pool is updated whenever a lower energy structure is found.
• The pool of structures is kept within a text file. This allows multiple instances of the code access to the structures.
Shayeghi, PCCP, 2014, Accepted
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Initialise Pool
Check Pool
Crossover
Minimise
StopConverged
Mutate
Check EnergyAgainst Pool
Minimise
ThrowAway
Higher Accept
Lower
Pop back in pool!
Pool Method
Selection
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Au20• The pool/database
methodology has been benchmarked and applied to Au20.
• The tetrahedral (Td) structure of Au20 has been predicted by both theory and experiment.
• The pool-BCGA successfully finds this as the global minimum.
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Au10 Ir8 Ir10
Davis, J. Phy. Chem. A, 2014, 114.
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Conclusions & Future Work
• Continue to test the code on a variety of systems.
• More mutation schemes.
• Ligand and surface optimisation.
• Implementation of a an SQL database.
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Acknowledgements • Roy Johnston.
• A. Shayeghi.
• Johnston Group.
• School of Chemistry
• Archer, Minerva and Bluebear HPCs.