Study leads to new cost-effective adiabatic connection methods for electron correlation energies

Accurately and efficiently calculating how electrons interact with each other lies at the heart of quantum chemistry. Recently, methods drawing on the adiabatic connection approach of density functional theory, using smooth conversions from the noninteracting to interacting systems of the computation, have proved useful for studying excitation energies in a variety of contexts. A new paper highlights recent advances of this method for computing electron correlation energies, and presents multiple approaches for doing so.

Holzer et al. conducted a systematic study of ways in which the Bethe-Salpeter equation, widely used for calculating optical properties in solids, can be applied to computations of atomic and molecular correlation energies. They did their study in the framework of the adiabatic connection fluctuation-dissipation theorem and aim to provide ways for computing atomic and molecular electronic energies using the laws of quantum mechanics.

With the so-called TURBOMOLE program package, the authors assessed the performance of several new techniques in various ways, including computing the total energies of the atoms of elements H through Ne on the periodic table. They found that the coupled-cluster infinite-order screened exchange approach showed promise as an accurate and cost-effective approach for computing correlation energies within the adiabatic framework.

“To our surprise, some of the methods available in the literature could not be generalized to atoms or molecules in magnetic fields, but it helped us to formulate new approaches,” said Wim Klopper, an author on the paper.

Klopper said he hopes the group’s findings will help stoke further interest in investigating which methods are both sufficiently accurate and cost-effective, as well as provide more insight into what makes adiabatic connection methods work well and what requires further investigation.

Source: “Bethe-Salpeter correlation energies of atoms and molecules,” by Christof Holzer, Xin Gui, Michael E. Harding, Georg Kresse, Trygve Helgaker, and Wim Klopper, The Journal of Chemical Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5047030 .