ECP-CCSD

Figure 25 The calculated energy change in the [2 + 2] cyclodimerization of chalcogen diimides E(NMe)2 (E = S, Se, Te). The calculations have been performed at LDA as well as at MP2/ECP, CCSD/ECP, and CCSD(T)/ECP levels of theory ( 2005 from Ref. 165 Reproduced by permission of Taylor Francis, Inc. http //www.taylorandfrancis.com)...

The work of Lee et al. [1113] compares results obtained with relativistic effective core potentials (ECP). The ECP calculations have been carried out with a Kramers-restricted (KR) two-component formalism as described in Ref. [836]. These results demonstrate the accuracy of the ECP-CCSD(T) approach when compared with experiment. Tsuchiya et al. [1115] investigated Au2 with MP2, CCSD and CCSD(T) employing a scalar-relativistic third-order DKH3 Hamiltonian. Again CCSD(T) yields results that reproduce all spectroscopic parameters remarkably well. 

Homonuclear dimers. In the first approximation, bonding in the solid state of an element is described by bonding in its homonuclear dimer, M2. Knowledge of the latter was, therefore, important to estimate AHsab of the bulk Cn. Moreover, Hg2 and Cn2 have been of a special interest in chemical theory in testing the accuracy of quantum chemical methods in treating closed-shell interactions. Accordingly, electronic structures of these dimers were calculated with the use of a various methods, such as 4c-BDF, ECP CCSD(T), QP PP CCSD(T) [204] and 4c-DFT [155, 198]. Results are summarized in Table 14 and Fig. 29. 

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