Quantitative molecular orbital energies within a G0W0 approximation
Using many-body perturbation theory within a G0W0 approximation, with a plane wave basis set and using a starting point based on density functional theory within the generalized gradient approximation, we explore routes for computing the ionization potential (IP), electron affinity (EA), and fundamental gap of three gas-phase molecules — benzene, thiophene, and (1,4) diamino-benzene — and compare with experiments. We examine the dependence of the IP and fundamental gap on the number of unoccupied states used to represent the dielectric function and the self energy, as well as the dielectric function plane-wave cutoff. We find that with an effective completion strategy for approximating the unoccupied subspace, and a well converged dielectric function kinetic energy cutoff, the computed IPs and EAs are in excellent quantitative agreement with available experiment (within 0.2 eV), indicating that a one-shot G0W0 approach can be very accurate for calculating addition/removal energies of small organic molecules.
KeywordsTopical issue: Challenges and solutions in GW calculations for complex systems. Guest editors: Feliciano Giustino, Paolo Umari and Angel Rubio
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