Exploring the Properties of Light Diatomic Molecules in Strong Magnetic Fields

Abstract: In this study, we develop and implement a specialized coupled-cluster (CC) approach tailored for accurately describing atoms and molecules in strong magnetic fields. Using the open-source Ghent Quantum Chemistry Package (\texttt{GQCP}) in conjunction with the Python-based Simulations of Chemistry Framework (\texttt{PySCF}), we calculate potential energy curves, permanent and transient dipole moments, as well as vibrational spectra for the diatomic molecules H$_2$, HeH$^+$ and LiH under various magnetic field strengths adopting a fully non-perturbative treatment. The main computational difficulties stem from the inclusion of the magnetic field in the Hamiltonian, in particular, from the presence of the angular momentum operator, which leads to a complication of the wave function and introduces a gauge-origin dependence. Addressing these challenges requires advanced modifications to existing routines, which we achieve by implementing gauge-comprising atomic orbitals (GIAOs) by using \texttt{GQCP}, and the capabilities offered by \texttt{PySCF}. This approach enhances the accuracy and reliability of the CC theory, opening pathways for more comprehensive investigations in molecular quantum chemistry at strong magnetic fields.