Computer-Aided Search for New Materials Using Quantum-Mechanics

Perhaps the most intriguing aspect of the spectacular success that semiconductor-based high technology has had in the past 50 years is the tiny number of species (core materials) on which these technologies are based. Even considering a broad range of semiconductor devices—transistor, computer chips, solid state lasers, detectors, solar cells, light-emitting diodes, etc.—there are only about ten basic semiconductors (all belonging to the same crystal type!), that enables these strategic technologies. This is a strikingly narrow material base, considering the number of core materials that enable other technologies: e.g., the 103–105 species used in metallurgy, polymer technologies, biotech, and the pharmaceutical drug industry. Thus, it is entirely possible that we are currently missing the crucial breakthrough material for present-day and future electronic devices. But how is one to search for new stable materials? Even if one considers only two types of atoms, there are as many as 2**N crystal structures possible on a lattice with N sites. Even for N=35, this equals the number of stars in our galaxy! Theoretical physicists at the National Renewable Energy Laboratory (NREL) in Golden, Colorado have developed a new strategy that enables one, using fast computers and concepts from Quantum Mechanics to search this astronomic space of possibilities for the "winning combination" of atoms producing novel, stable crystal structures. This approach—Linear Expansion in Geometric Objects (LEGO)—is based on the recognition that even complex crystal structures can be viewed as a collection of simple Geometric Objects such as pairs of atoms (dumbbells), triangles of atoms, etc. By assigning to each Geometric Object an (quantum-mechanical) energy value, one can rapidly scan hundreds of thousands of candidate structures (obtained by different assemblies of the Geometric Objects), looking for the one with the lowest overall energy. This LEGO approach has already predicted a number of previously unsuspected intermetallic compounds, that were missed by the conventional approach of trial-and-error. This could revolutionize the way in which novel materials are sought.

Online Presentation of LEGO methodology

We have an online presentation describing the LEGO methodology in HTML

Selected References

  1. A. Zunger, "First Principles Statistical Mechanics of Semiconductor Alloys and Intermetallic Compounds," in NATO Advanced Study Institute on Statics and Dynamics of Alloy Phase Transformations, edited by P. Turchi and A. Gonis, Plenum Press, New York, 361-419 (1994).

Other References

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