Numerical analysis of the complete active-space extended Koopmans’s theorem

What is it about?

In this study, we explore the accuracy of a new approach, the complete active-space extended Koopmans's theorem (CAS-EKT) in calculating ionization energies (IEs) of atomic and molecular systems. By comparing CAS-EKT results with exact ionization energies from advanced quantum chemistry methods, we highlight how increasing basis set size improves accuracy. Our findings provide valuable insights for researchers aiming to enhance the precision of ionization energy calculations, especially for spectroscopic studies of small molecules like lithium hydride (LiH).

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Photo by Norbert Kowalczyk on Unsplash

Photo by Norbert Kowalczyk on Unsplash

Why is it important?

Our findings show a fundamental challenge in computational chemistry for accurately calculating ionization energies (IEs) of atoms and molecules. Ionization energies are crucial for understanding chemical reactivity, molecular properties, and spectroscopic behavior. By investigating the extended Koopmans's theorem (EKT) within both full configuration interaction (FCI) and complete active space configuration interaction (CAS-CI) frameworks, this research pushes the boundaries of computational accuracy, revealing how basis set choices and the active space size impact the precision of calculated IEs.

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