Correlation consistent basis sets methodology

In the present work, correlation consistent basis sets have been developed for the transition metal atoms Y and Hg using small-core quasirelativistic PPs, i.e., the ns and (nA)d valence electrons as well as the outer-core (nA)sp electrons are explicitly included in the calculations. This can greatly reduce the errors due to the PP approximation, and in particular the pseudo-orbitals in the valence region retain some nodal structure. Series of basis sets from double-through quintuple-zeta have been developed and are denoted as cc-pVwZ-PP (correlation consistent polarized valence with pseudopotentials). The methodology used in this work is described in Sec. II, while molecular benchmark calculations on YC, HgH, and Hg2 are given in Sec. III. Lastly, the results are summarized in Sec. IV. 

The concomitant advances in theoretical methodologies and algorithms have also played a vital role in increasing computational capabilities for theoretical thermochemistry. These advances include (1) new methods for accurate treatment of electron correlation in molecules and atoms such as coupled cluster and quadratic configuration interaction methods, (2) new basis sets such as the correlation consistent basis sets, and (3) development of model chemistry ... 

The first iteration of the ccCA methodology modeled the popular and successfiil Gn methods [79]. In fact, similar to the G3 method, the initial formulation of ccCA sought as its effective level of theory QCISD(T) with large basis sets and some aceount of core-valence correlation. However, ccCA utilized the larger and more flexible correlation consistent basis sets instead of the Pople-style sets adopted by the Gn authors, which we felt would enable the more systematic behavior of the... 

The ccCA methodology was first used to compute the enthalpies of formation of oxides and hydroxides of Li, Be, Na, or Mg metal ions. The computations were performed using newly optimized correlation consistent basis sets for the metals... 

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