  Heavy polar diatomic molecules are the primary tools for searching for the
T-violating permanent electric dipole moment of the electron (eEDM). Valence
electrons in some molecules experience extremely large effective electric
fields due to relativistic interactions. These large effective electric fields
are crucial to the success of polar-molecule-based eEDM search experiments.
Here we report on the results of relativistic ab initio calculations of the
effective electric fields in a series of molecules that are highly sensitive to
an eEDM, the mercury monohalides (HgF, HgCl, HgBr,and HgI). We study the
influence of the halide anions on effective electric field, and identify HgBr
and HgI as interesting candidates for future electric dipole moment search
experiments.
