The performance of different GW methods is assessed for a set of 24 organic acceptors. Errors are evaluated with respect to coupled cluster singles, doubles, and perturbative triples [CCSD(T)] reference data for the vertical ionization potentials (IPs) and electron affinities (EAs), extrapolated to the complete basis set limit. Additional comparisons are made to experimental data, where available. We consider fully self-consistent GW (scGW), partial self-consistency in the Green's function (scGW0), non-self-consistent G0W0 based on several mean-field starting points, and a "beyond GW" second-order screened exchange (SOSEX) correction to G0W0. We also describe the implementation of the self-consistent Coulomb hole with screened exchange method (COHSEX), which serves as one of the mean-field starting points. The best performers overall are G0W0+SOSEX and G0W0 based on an IP-tuned long-range corrected hybrid functional with the former being more accurate for EAs and the latter for IPs. Both provide a balanced treatment of localized vs delocalized states and valence spectra in good agreement with photoemission spectroscopy (PES) experiments.

Several isomeric structures of the uracil−water complex and its covalent-bound anion were calculated ab initio with second-order, many-body, perturbation theory and the 6-311++G** basis set. In all neutral complexes, water forms two hydrogen bonds with uracil. In each of the conventional anionic forms, a single, but stronger and shorter, hydrogen bond is found. All complexes are nonplanar, but ring-puckering is less pronounced in neutrals than in anions. Several isomers of the anionic uracil−water complex have positive adiabatic electron-detachment energies. The existence of multiple anionic isomers with vertical electron-detachment energies between 0.30 and 0.90 eV accounts for the broad photoelectron spectrum. The lowest unoccupied molecular orbital of the neutral complex at the geometry of the anionic complex provides a simple explanation for the structural and energetic consequences of electron attachment.

In designing organic materials for electronics applications, particularly for organic photovoltaics (OPV), the ionization potential (IP) of the donor and the electron affinity (EA) of the acceptor play key roles. This makes OPV design an appealing application for computational chemistry since IPs and EAs are readily calculable from most electronic structure methods. Unfortunately reliable, high-accuracy wave function methods, such as coupled cluster theory with single, double, and perturbative triples [CCSD(T)] in the complete basis set (CBS) limit are too expensive for routine applications to this problem for any but the smallest of systems. One solution is to calibrate approximate, less computationally expensive methods against a database of high-accuracy IP/EA values; however, to our knowledge, no such database exists for systems related to OPV design. The present work is the first of a multipart study whose overarching goal is to determine which computational methods can be used to reliably compute IPs and EAs of electron acceptors. This part introduces a database of 24 known organic electron acceptors and provides high-accuracy vertical IP and EA values expected to be within ±0.03 eV of the true non-relativistic, vertical CCSD(T)/CBS limit. Convergence of IP and EA values toward the CBS limit is studied systematically for the Hartree-Fock, MP2 correlation, and beyond-MP2 coupled cluster contributions to the focal point estimates.

Electron propagator methods are applied to the ionization energies of the five most stable tautomers of guanine. Excellent agreement with gas-phase photoelectron spectra is obtained for the amino-oxo form of 7H-guanine. According to ionization energy assignments, both 9H-guanine and its amino-oxy tautomers also may be present in the gas phase. The presence of amino-oxy 7H-guanine, however, is less certain, due to its higher total energy. In all cases, the lowest ionization occurs from a π level. There are strong correlation effects for higher cationic states. Energy orderings of π and σ hole states are different for each of the isomers.

Photoelectron spectra of deoxyribonucleotide anions are interpreted with ab initio, electron propagator calculations. Ground-state structures display hydrogen bonds which are not present in less stable minima that resemble Watson-Crick fragment geometries. For the adenosine and thymidine anions, there are two vertical electron detachment energies (VEDEs) within 0.1 eV of each other that correspond to phosphate- and base-centered Dyson orbitals (DOs). The first VEDE of the cytidine anion belongs to a phosphate-centered DO. The anomalously low VEDE of the guanosine anion is assigned to a base-centered, pi DO. Higher VEDEs of all four anions also are assigned.