Alex Zunger
Alex Zunger is a Fellow at the National Renewable Energy Laboratory.
Title: Quantum-Mechanical Combinatorial Design of Solids with Target Properties
One of the most striking aspects of solid-state physics is the diversity of structural forms in which crystals appear in Nature. The already rich repertoire of such (equilibrium) forms has recently been significantly enriched by the advent of artificial growth techniques (MBE, STM- atom positioning, etc) that can create desired structural forms, such as superlattices and geometric atomic clusters even in defiance of the rules of equilibrium thermodynamics.
As is well known, different atomic configurations generally lead to different physical properties even at fixed chemical composition. While the most widely-known illustration of such “form controls function” rule is the dramatically different color, conductivity and hardness of the allotropical forms of pure carbon, the physics of semiconductor superstructures and nanostructures is full of striking examples of how optical, magnetic and transport properties depend sensitively on atomic configuration (e.g, compare the properties of random to ordered alloys).
Yet, the history of material research generally proceeded via accidental discoveries of materials configuration with interesting physical property (semiconductivity, ferromagnetism; superconductivity etc). Given the ability of growing many different atomic configurations, and given the often sensitive dependence of physical properties on atomic configuration, makes one wonder: can one first articulate the desired target physical property, then search (within a class) for the configuration that has this property?
This talk describes the recent steps made by solid-state theory and computational physics to address this “Inverse Design“ problem. I will show how Genetic Algorithms, in combination with efficient (“Order N“) solutions to the Pseudopotential Schrödinger equation allow us to investigate astronomical spaces of atomic configurations in search of the structure with a target physical problem. Only a small fraction of all (~ 10^14 in our case) configurations need to be examined. Examples will include Band-Gap design in superlattices; architecture of impurity–clusters with desired optical properties, and Inverse Design of the Curie temperature in dilute magnetic systems.
This work was performed in collaboration with A. Franceschetti, P. Piquini, S. Duidy.
Additional Reading might include:
P. Piquini and A. Zunger “Using superlattice ordering to reduce the band gap of random (In,Ga)As/InP alloys to a target value via the inverse band structure approach” Phys. Rev. B ,Rapid Communication, 78, 161302(R) (2008) (pdf link)
M. d'Avezac and A. Zunger “ Identifying the minimum-energy atomic configuration on a lattice: a Lamarckian twist on Darwinian evolution” Phys. Rev. B 78, 064102 (2008). (pdf link).
P. Piquini, P. A. Graf, and A. Zunger “ Band gap design of quarternary (In,Ga)(As,Sb) semiconductors via the inverse band structure approach” Physical Review Letters 100, 186403 (2008). (pdf link).
G. L.W. Hart, Volker Blum, Michael J. Walorski, and Alex Zunger, “ Evolutionary Approach for Determining First-Principles Hamiltonian” , Nature Materials 4, 391 (2005) (pdf link) .
A Franceschetti, S. V. Dudiy, S. V. Barabash, A. Zunger, J. Xu, and M. van Schilfgaarde “ First-Principles Combinatorial Design of Transition Temperatures in Multicomponent Systems: The Case of Mn in GaAs” Physical . Review . Letters . 97, 047202 (2006) (pdf link).
S.V. Dudiy and Alex Zunger, “ Searching for Alloy Configurations with Target Physical Properties: Impurity Design via a Genetic Algorithm Inverse Band Structure Approach” , Physical . Review Letters t. 97, 046401 (2006). (pdf link).
J.-W. Luo, A. Franceschetti, and A. Zunger “ Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects” Nano Letters 8 (10), 3174-3181 (2008) (http://www.sst.nrel.gov/nano_pub/nl801459h.pdf pdf link]).
