Full configuration interaction calculation of BeH adiabatic states

The Shape of Full Configuration Interaction to Come

We present a Perspective on what the future holds for full configuration interaction (FCI) theory, with an emphasis on conceptual rather than technical details. Upon revisiting the early history of FCI, a number of its key contemporary approximations are compared on as equal a footing as possible, using a recent blind challenge on the benzene molecule as a testbed [Eriksen et al., J. Phys. Chem. Lett., 2020 11, 8922]. In the process, we review the scope of applications for which FCI continues to prove indispensable, and the required traits in terms of robustness, efficacy, and reliability its modern approximations must satisfy are discussed. We close by conveying a number of general observations on the merits offered by the state-of-the-art alongside some of the challenges still faced to this day. While the field has altogether seen immense progress over the years-the past decade, in particular-it remains clear that our community as a whole has a substantial way to go in enhancing the overall applicability of near-exact electronic structure theory for systems of general composition and increasing size.

Theoretical investigation on the low-lying electronic states of beryllium antimonide

The Λ-S electronic states with respect to the lowest four dissociation limits of BeSb are investigated theoretically on the icMRCI + Q level employing basis set of quintuple-ζ quality. The geometrical parameters, potential energy curves, vibrational energy levels, spectroscopic constants for the twelve Λ - S states are obtained, analyzed and compared with those of the Beryllium-VA group diatomic family species where data are available. The permanent dipole moments, transition dipole moments, Einstein emission coefficients, radiative lifetimes and Franck-Condon factors for interested Λ - S states are also derived. Further assessments of the spin-orbit coupling effect are performed for states associated with the first two dissociation asymptotes of BeSb. Four Λ - S states split into seven Ω states, and some of the PECs are distorted significantly through the spin-orbit coupling effect, which is similar to its isovalent diatomics BeAs. In consideration of potential risks of manipulating beryllium-containing species directly, the information associated with molecular structures, spectroscopic parameters as well as transition properties that provide in this paper is anticipated to serve as guidelines for further researches of BeSb.

Quantum Interference Contribution to the Dipole Moment of Diatomic Molecules

The interference energy partitioning analysis method developed by our group and used to study the nature of the chemical bond was extended to partition the electric dipole moment in quasi-classical and interference contributions. Our results show that interference participates in charge displacement in polar molecules, providing, directly or indirectly, a relevant contribution for the total dipole moment. A linear correlation was found between the interference contribution of the dipole moment from the bond electron group, μ_INT(bond), and the difference of electronegativity of the atoms which form the bond, ΔX_AB. This interesting result reinforces the fact that electronegativity is not a property of an atom alone, but rather a property of the atom in the molecule and that ΔX_AB can only be associated with that part of the total charge displacement resulting from the formation of the chemical bond. The partitioning of the total dipole moment into quasi-classical and interference contributions provides new insights about the reasons for the failure of the ΔX_AB criterion in predicting the correct orientation of the dipole moment in several molecules. The results of the present work also bring additional evidence for the previously proposed mechanism of formation of polar bonds.