Molecular Electron Affinities Using the Generalized Kohn-Sham Semicanonical Projected Random Phase Approximation.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of electron affinities is crucial for understanding molecular properties and reactivity.
• Existing methods may struggle with the accurate description of anionic systems, particularly those involving diffuse or non-valence states.

Purpose of the Study:

• To investigate the suitability of one-particle energies from the generalized Kohn-Sham semicanonical projected random phase approximation (GKS-spRPA) for predicting molecular electron affinities.
• To develop and present an efficient computational implementation of the GKS-spRPA method for fast electron affinity calculations.

Main Methods:

• Utilizing the GKS-spRPA method, which incorporates exact exchange and polarizability-dependent correlation terms.
• Comparing GKS-spRPA results with high-level equation of motion coupled cluster methods for validation.
• Applying the method to model systems and a series of perhalobenzene molecules (C6X6).

Main Results:

• The GKS-spRPA method demonstrates high accuracy for electron affinities, with maximum errors of 0.13 eV for valence and 0.03 eV for nonvalence anionic states.
• The GKS-spRPA effective potential correctly accounts for necessary terms for describing anionic systems.
• For perhalobenzenes, a transition in ground-state character from nonvalence-σ* to valence-π* or valence-σ* is predicted with increasing halogen size.

Conclusions:

• The GKS-spRPA method is a suitable and efficient approach for calculating molecular electron affinities.
• The findings provide insights into the electronic structure of anionic perhalobenzene molecules.
• The study highlights the potential for experimental verification of predicted electronic state transitions.