Electron Propagator Theory: Fourth Order Diagrams, Composite Approach and Application to Anions, Superhalides and Double–Rydberg Anions

Abstract

The Electron Propagator Theory is useful for calculating vertical electron detachment energies and Dyson orbitals of neutral molecules and anions. The Electron Propagator Theory is a second quantization method that can be improved systematically by increasing the Super–Operator space or improving the order of couplings. In this work, a software (DROGON .D4) is used to obtain expressions, plots and program 316 fourth–order Brandow–type diagrams. The combination of high correlation methods with complete basis sets is usually unfeasible for moderate–large molecular systems. For this reason, composite approaches are common for the high accuracy prediction of molecular and thermochemical properties. In this work, the exploration of the composite approach begins with an Electron Propagator Benchmark of methods for neutral molecules and anions in addition to the statistical study of additive properties of basis sets and high correlation effects. Then, composite electron propagator methods are defined and tested: CP3+/34, CN/34 are good approximations for neutral molecules with mean unsigned errors of 0.08 and 0.14 eV, respectively. For anions, CP3+/a23, CP3+/a34, CNR2/a23 and CNR2/a34 yield mean unsigned errors of 0.11, 0.12, 0.15 and 0.12 eV, respectively. Case studies of several anions of interest are analyzed: P2N3- is a pentagonal ring with several accessible electronic states for its neutral form. The first vertical electron detachment energy is 4.41 eV and corresponds to a 2A1 state. Its lower energy isomer, N2PNP- is also apentagonal ring with a lower vertical electron detachment energy of 3.73 eV corresponding to a 2B2 final state. In addition, vertical electron detachment energies for superhalides have been studied for Al(BO2)4- , Mg2(CN)5-, CHB11H11- , CHB11F11- and CHB11Cl11-