Analytic Calculation of Contact Densities and Mössbauer Isomer Shifts Using the Normalized Elimination of the Small-Component Formalism.

The analytic linear response formalism for the calculation of the effective contact densities ρ̅ in the context of the normalized elimination of the small component (NESC) method is developed and implemented. The formalism is tested for the calculation of contact densities and contact density differences in a series of mercury cations and mercury-containing molecules. The calculations carried out at the NESC/SCF, NESC/MP2, and NESC/CCSD levels of theory demonstrate high sensitivity of the contact density to the local coordination environment and the oxidation state of mercury. The NESC/MP2 results are in a very good agreement with the NESC/CCSD ones, which suggests that the former method can be used as a cost-effective alternative to high-level ab initio calculations.