Accurate calculation of quasparticle energies and band gaps in molecules and nanclusters is highly desirable in the field of photovoltaics. Common DFT techniques, however, greatly underestimate band gaps. The GW approximation offers a reliable and accessible theory for calculating quasiparticle energies and band gaps with high accuracy, though practical application of GW for large systems is limited by very steep CPU and memory requirements as system size increases. We therefore present a new formalism for calculating quasiparticle energies within the GW approximation. In our method, the occupied and virtual Kohn-Sham orbitals are replaced by stochastic orbitals used to calculate the Green's function and the polarization potential, and thereby the GW self-energy. The method achieves near-linear scaling, allowing for one to calculate quasipartcle energies in systems prohibitively large for traditional approaches. We first illustrate the method for silicon nanoclusters of varying sizes (up to several thousand electrons). We then apply the method to a variety of organic semiconductors of experimental interest in the field of organic photovoltaics.

Stochastic GW: Formulation and application to nanoclusters

248th National Meeting (2014)

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