Quantitative molecular orbital energies within a G0W0 approximation

Abstract

Using many-body perturbation theory within the G0W0 approximation, we explore routes for computing the ionization potential (IP), electron affinity (EA), and fundamental gap of three gasphase molecules -benzene, thiophene, and (1,4) diamino-benzene -and compare with experiments.We examine the dependence of the IP on the number of unoccupied states used to build 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 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. Our results indicate that a sufficient dielectric function kinetic energy cutoff may be the limiting step for a wide application of G0W0 to larger organic systems. arXiv:1204.0509v1 [cond-mat.mtrl-sci]

Excitation spectra of aromatic molecules within a real-spaceGW-BSE formalism: Role of self-consistency and vertex corrections

“…[66][67][68] To accelerate convergence of the sumover-transitions (poles of the polarizability), we compute the self energy at various levels of convergence (N states satisfying E DFT (N states ) = {20, 30, ..., 90} eV where E DFT (N states ) is the Kohn-Sham DFT eigenvalue of the highest-energy state included in the G and polarizability summations), and obtain a weighted 1/N states extrapolation for a best estimate of numerically converged GW self energies. [68][69][70] The extrapolation produces IPs 50-100 meV larger than the most converged calculation. Note that while we choose the same cutoff of N states for both the calculation of the polarizability and the sum over states, different cutoffs can be applied to these separate summations.…”

Benchmark ofGWmethods for azabenzenes

“…This leads to the notoriously slow convergence of GW calculations with respect to the number of unoccupied states. 35,39,146,147 The localized nature of the NAO basis sets contributes to a faster convergence with basis set size than that of planewave basis sets. Here, we show a representative example of the basis set convergence for pyrimidine.…”

Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional

“…A rigorous formalism for quasiparticle energies is many-body perturbation theory (MBPT), which in practice is most often used in the GW approximation, 20,21 where G is the single-particle Green's function and W is the screened Coulomb interaction. GW has been shown to be an accurate approach for a wide range of molecules [22][23][24][25][26][27] and bulk solids. [28][29][30] However, several issues have hindered the widespread use of GW calculations for molecule-metal interfaces.…”

“…[31][32][33][34] Moreover, several benchmarking studies, including work on smaller molecule-metal systems, also showed that results from perturbative GW calculations can be challenging and expensive to converge numerically. 23,35,36 Furthermore, it is by now well known that single-shot GW calculations often depend on the underlying starting point, 22,37,38 which adds additional complications for efficient GW calculations of large-scale molecule-metal interfaces and their functional properties.…”