Full configuration interaction calculation of BeH adiabatic states

Area of Science:

• Quantum Chemistry
• Theoretical Spectroscopy
• Computational Molecular Physics

Background:

• Accurate theoretical descriptions of molecular electronic states are crucial for understanding chemical bonding and reactivity.
• Beryllium hydride (BeH) is a simple diatomic molecule serving as a benchmark system for computational methods.

Purpose of the Study:

• To perform all-electron full configuration interaction (FCI) calculations for the adiabatic potential energy curves of lower electronic states of BeH.
• To investigate the interactions between valence and Rydberg states and report dipole moments and transition dipole strengths.
• To analyze avoided crossings and calculate spectroscopic parameters for various electronic states.

Main Methods:

• Employed an all-electron full configuration interaction (FCI) method.
• Utilized a moderately large atomic natural orbital (ANO) basis set augmented with Rydberg functions on the Be atom.
• Calculated adiabatic potential energy curves, dipole moments, and transition dipole strengths as a function of internuclear distance R(Be-H).

Main Results:

• Resolved the 'D complex' into three 3d substates and characterized a diexcited valence state of 2Sigma(-) symmetry.
• Identified a swallow well in the 4(2)Sigma(+) state due to an avoided crossing with the 3(2)Sigma(+) state, with a high probability of vibrational population.
• Found that the calculated spectroscopic properties of the 6(2)Sigma(+) adiabatic curve agree with experimental data for the F(4psigma) (2)Sigma(+) state, with no evidence of the E(4ssigma) (2)Sigma(+) state in the 'D complex' region.

Conclusions:

• The FCI calculations provide benchmark results for the open-shell BeH system, highlighting the capabilities and limitations of the chosen basis set.
• The study elucidates the complex electronic structure of BeH, including interactions between different types of electronic states and the nature of avoided crossings.
• Spectroscopic parameters derived from the calculated potential energy curves offer valuable data for experimentalists and further theoretical investigations.