  Mercury monohalides are promising candidates for electron electric dipole
moment searches. This is due to their extremely large values of effective
electric fields, besides other attractive experimental features. We have
elucidated the theoretical reasons of our previous work. We have also presented
a detailed analysis of our calculations, by including the most important of the
correlation effects' contributions. We have also analyzed the major
contributions to the effective electric field, at the Dirac- Fock level, and
identified those atomic orbitals' mixings that contribute significantly to it.
