title: NR2 and P3+: Accurate, Efficient Electron-Propagator Methods for Calculating Valence, Vertical Ionization Energies of Closed-Shell Molecules.
abstract: Two accurate and computationally efficient electron-propagator (EP) methods for calculating the valence, vertical ionization energies (VIEs) of closed-shell molecules have been identified through comparisons with related approximations. VIEs of a representative set of closed-shell molecules were calculated with EP methods using 10 basis sets. The most easily executed method, the diagonal, second-order (D2) EP approximation, produces results that steadily rise as basis sets are improved toward values based on extrapolated coupled-cluster singles and doubles plus perturbative triples calculations, but its mean errors remain unacceptably large. The outer valence Green function, partial third-order and renormalized partial third-order methods (P3+), which employ the diagonal self-energy approximation, produce markedly better results but have a greater tendency to overestimate VIEs with larger basis sets. The best combination of accuracy and efficiency with a diagonal self-energy matrix is the P3+ approximation, which exhibits the best trends with respect to basis-set saturation. Several renormalized methods with more flexible nondiagonal self-energies also have been examined: the two-particle, one-hole Tamm-Dancoff approximation (2ph-TDA), the third-order algebraic diagrammatic construction or ADC(3), the renormalized third-order (3+) method, and the nondiagonal second-order renormalized (NR2) approximation. Like D2, 2ph-TDA produces steady improvements with basis set augmentation, but its average errors are too large. Errors obtained with 3+ and ADC(3) are smaller on average than those of 2ph-TDA. These methods also have a greater tendency to overestimate VIEs with larger basis sets. The smallest average errors occur for the NR2 approximation; these errors decrease steadily with basis augmentations. As basis sets approach saturation, NR2 becomes the most accurate and efficient method with a nondiagonal self-energy.
authors.affiliation: †Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States.
authors.forename: H H
authors.initials: HH
authors.lastname: Corzo
authors.affiliation: ‡Departamento de Química, Universidad Autónoma Metropolitana, Iztapalapa San Rafael Atlixco 186, Col. Vicentina, Iztapalapa, C.P. 09340, México, D.F., Mexico.
authors.forename: Annia
authors.initials: A
authors.lastname: Galano
authors.affiliation: †Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States.
authors.forename: O
authors.initials: O
authors.lastname: Dolgounitcheva
authors.affiliation: †Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States.
authors.forename: V G
authors.initials: VG
authors.lastname: Zakrzewski
authors.affiliation: †Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849-5312, United States.
authors.forename: J V
authors.initials: JV
authors.lastname: Ortiz