Olivia Hull, Kansas State University

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The GW method is a highly accurate ab initio quantum mechanical technique for understanding the electronic structure of solids and surfaces. The evaluation of quantities within the GW approximation requires a double summation over occupied/virtual state pairs. Thus, information regarding which individual quantum states contribute to a specific quantity is encoded in the computation of the quantity. BerkeleyGW, an implementation of the GW method, has made GW calculations on systems of hundreds of atoms tractable due to its massive parallelism. Its parallelization scheme is intimately related to the sum-over-states computation, as it distributes occupied/virtual state pairs across MPI tasks. We have modified the BerkeleyGW parallelization scheme so that any number of individual states can be excluded from the double summation involved in calculating a quantity. Using this method, we selectively exclude various states from the GW computation of the polarizability of GaN, allowing us to study the origin of shoulder peaks in the plasmon excitation of the GaN electron energy loss spectrum. We find that interactions between Ga d-states and the valence bands are the source of these spectral features.

Abstract Author(s): Olivia Hull, Derek Vigil-Fowler