A quarterly research and development magazine.
Predicting a material’s properties by first calculating its electronic structure could cut down experimental time and lead researchers to uncover new materials with unexpected benefits. But commonly used simulations are often inaccurate. This is especially so for materials like silicon, whose strongly correlated electrons influence each other over a distance and make simple calculations difficult.
Now a team of researchers at Sandia are looking at a solution that offers huge potential. Using LDRD and DOE Office of Science funding, Sergey Faleev and his colleagues have applied theoretical innovations and novel algorithms to make a hard-to-use theoretical approach from 1965 amenable to computation. The team’s approach may open the door to discovering new phases of matter, creating new materials, or optimizing performance of compounds and devices, such as alloys and solar cells.
A paper on this subject, “Quasiparticle Self-Consistent GW Theory,” appeared last year in Physical Review Letters. “GW” in the title refers to Lars Hedin’s 1965 theory that elegantly predicts electronic energy for ground and excited states of materials. “G” stands for the Greens function — used to derive potential and kinetic energy. “W” is the screened Coulomb interaction, which represents electrostatic force acting on the electrons. “Quasiparticle” is used to describe particle-like behavior in a complex system of interacting particles. Selfconsistent means the particle’s motion and effective field, which determine each other, are iteratively solved, coming closer and closer to a solution until the result stops changing.
“Our code has no approximation except GW itself,” said Faleev. “It’s considered to be the most accurate of all GW implementations to date.”
“It works well for everything in the periodic table,” adds coauthor Mark van Schilfgaarde, a former Sandian now at Arizona State University. The paper reports results for diverse materials, whose properties cannot be consistently predicted by any other theory. The 32 examples include alkali metals, semiconductors, wide band-gap insulators, transition metals, transition metal oxides, magnetic insulators, and rare earth compounds.