Application of the finite-field coupled-cluster method to calculate molecular properties relevant to electron electric-dipole-moment searches

Heavy polar diatomic molecules are currently among the most promising probes of fundamental physics. Constraining the electric dipole moment of the electron ($e\mathrm{EDM}$), in order to explore physics beyond the standard model, requires a synergy of molecular experiment and theory. Recent advances in experiment in this field have motivated us to implement a finite-field coupled-cluster (FFCC) approach. This work has distinct advantages over the theoretical methods that we had used earlier in the analysis of $e\mathrm{EDM}$ searches. We used relativistic FFCC to calculate molecular properties of interest to $e\mathrm{EDM}$ experiments, that is, the effective electric field ($E_{\mathrm{eff}}$) and the permanent electric dipole moment (PDM). We theoretically determine these quantities for the alkaline-earth monofluorides (AEMs), the mercury monohalides ($\mathrm{Hg}X$), and PbF. The latter two systems, as well as BaF from the AEMs, are of interest to $e\mathrm{EDM}$ searches. We also report the calculation of the properties using a relativistic finite-field coupled-cluster approach with single, double, and partial triples’ excitations, which is considered to be the gold standard of electronic structure calculations. We also present a detailed error estimate, including errors that stem from our choice of basis sets, and higher-order correlation effects.