Permanent electric dipole moment of diatomic molecules using relativistic extended–coupled–cluster method

We employ the four-component relativistic extended–coupled–cluster (ECC) method, a variational coupled–cluster (CC) approach, to compute the permanent electric dipole moment (PDM) of open-shell diatomic molecules (CaH, CaF, SrH and SrF) in their ground electronic state. The ECC results are compared with the PDM values estimated by the experiments as well as other single-reference CC-based approaches (the Z-vector technique, the expectation value method and the finite field approach) within the four-component relativistic framework to test the efficacy of the employed method. Our study reveals that the relativistic ECC method can yield reliable results for the PDMs of the considered molecular systems. We also observe that the computed results of the dipole moment improve upon the augmentation of diffused functions to the basis set.