O. Dolgounitcheva

Structures and electron detachment energies of uracil anions

Abstract Uracil and its radical anions were studied with second-order, many-body perturbation theory, coupled-cluster theory and electron propagator methods with large, diffuse, atom-centered basis sets. All structures were optimized and two minima were found for anionic forms: one corresponding to a 2 A′, diffuse-bound state and another corresponding to a 2 A, non-planar, covalent-bound state. The optimized 2 A′ anionic structure is lower in energy than the neutral form. The vertical electron detachment energy (VEDE) of this structure is very close to the experimentally observed value. A large, positive VEDE was found for the 2 A, covalent-bound anion.

One-Electron Pictures of Electronic Structure: Propagator Calculations on Photoelectron Spectra of Aromatic Molecules

Hartree-Fock [1] and density functional [2, 3] theories offer one-electron pictures of molecular electronic structure. The former has been the standard by which the concept of electron correlation has been defined [4] and its errors therefore are known as correlation effects. Density functional theories provide a variety of exchange and correlation approximations that can be incorporated into orbital eigenvalue equations. The widespread application of methods based on the Kohn-Sham equations [5] attests to the appeal of the one-electron paradigm.

Ground state and vertical electron detachment energies of icosahedral and D5h Al13

Al13− clusters are studied with ab initio, many-body methods. Coupled-cluster theory places the icosahedral structure 0.54 eV lower than the D5h isomer. Electron propagator predictions on the photoelectron spectrum of Al13− are in close agreement with the observed bands and attribute shakeup character to features at higher energy.

Electron-propagator calculations on the photoelectron spectrum of ethylene

Electron-propagator calculations are performed on the vertical ionization energies of ethylene with a sequence of correlation-consistent basis sets. Two methods are employed: the nondiagonal, renormalized, second-order (NR2) approximation and the third-order, algebraic, diagrammatic construction. The computational efficiency of the NR2 method permits the use of the correlation-consistent, pentuple ζ basis, which contains 402 contracted Gaussian functions. As the size of the basis set grows, NR2 results for outer-valence ionization energies steadily increase; NR2 errors with the largest basis set are less than ∼0.15 eV. Agreement with prominent, inner-valence peaks is also satisfactory and the ratio of two pole strengths corresponding to inner-valence, 2Ag states is in close agreement with observed intensity ratios.

Efficient electron propagator algorithms for shakeup final states: Anthracene and acridine

A new algorithm was reported previously for renormalized electron propagator methods that are appropriate for shakeup final states. These methods include the algebraic diagrammatic construction in the third order, the two-particle, one-hole Tamm–Dancoff approximation and the nondiagonal, renormalized, second-order approximation. To demonstrate the capabilities of this approach, results on anthracene and acridine are presented. Good agreement with photoelectron spectra are obtained. The orbital picture of ionization collapses for many final states at relatively low ionization energies.

Ionization energies of benzo[a]pyrene and benzo[e]pyrene

Photoelectron spectra of benzo[a]pyrene and benzo[e]pyrene have been assigned on the basis of ab initio electron propagator theory. Electron correlation effects are included in the partial third order approximation and agreement with experimental peaks is very close. To each ionization energy, there corresponds a Feynman–Dyson amplitude that exhibits the change in electronic structure associated with the removal of an electron. Correlation corrections to the Koopmans description of the cationic states are large for many states, but the qualitative validity of this model remains valid. The lowest final states with σ holes occur around 11.0 eV.

Structure, bonding, and energetics of C72− isomers

Several isomers of C72− were studied with electron correlation methods and augmented, correlation-consistent basis sets. All are thermodynamically stable with respect to dissociation into C5− and C2− anions. Isomerization energies are less than 5 kcal/mol at the highest level of theory. Vertical and adiabatic electron detachment energies are positive for the D3h form of C72−. Linear, carbene, bridged-chain, and chain-ring isomers are considered as well. Feynman–Dyson amplitudes connecting dianionic and anionic states reveal extensive delocalization of the least bound electrons.