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Cubic-scaling algorithm and self-consistent field for the random-phase approximation with second-order screened exchange

Journal of Chemical Physics

Moussa, Jonathan E.

The random-phase approximation with second-order screened exchange (RPA+SOSEX) is a model of electron correlation energy with two caveats: its accuracy depends on an arbitrary choice of mean field, and it scales as O(n 5) operations and O(n3) memory for n electrons. We derive a new algorithm that reduces its scaling to O(n3) operations and O(n2) memory using controlled approximations and a new self-consistent field that approximates Brueckner coupled-cluster doubles theory with RPA+SOSEX, referred to as Brueckner RPA theory. The algorithm comparably reduces the scaling of second-order Møller-Plesset perturbation theory with smaller cost prefactors than RPA+SOSEX. Within a semiempirical model, we study H2 dissociation to test accuracy and Hn rings to verify scaling. © 2014 AIP Publishing LLC.

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TYPE Journal Article YEAR 2014
OSTIScopus

Simulation and modeling of the electronic structure of GaAs damage clusters

Journal of Applied Physics

Moussa, Jonathan E.; Foiles, Stephen M.; Schultz, Peter A.

In an effort to build a stronger microscopic foundation for radiation damage models in gallium arsenide (GaAs), the electronic properties of radiation-induced damage clusters are studied with atomistic simulations. Molecular dynamics simulations are used to access the time and length scales required for direct simulation of a collision cascade, and density functional theory simulations are used to calculate the electronic properties of isolated damaged clusters that are extracted from these cascades. To study the physical properties of clusters, we analyze the statistics of a randomly generated ensemble of damage clusters because no single cluster adequately represents this class of defects. The electronic properties of damage clusters are accurately described by a classical model of the electrical charging of a semiconducting sphere embedded in a uniform dielectric. The effective band gap of the cluster depends on the degree of internal structural damage, and the gap closes to form a metal in the high-damage limit. We estimate the Fermi level of this metallic state, which corresponds to high-energy amorphous GaAs, to be 0.46 ± 0.07 eV above the valence band edge of crystalline GaAs. © 2013 American Institute of Physics.

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TYPE Journal Article YEAR 2013
OSTIScopus
Results 26–43 of 43
Results 26–43 of 43