Tight polarization functions

The MP2 and CCSD(T) values in Tables 11.2 and 11.3 are for correlation of the valence electrons only, i.e. the frozen core approximation. In order to asses the effect of core-electron correlation, the basis set needs to be augmented with tight polarization functions. The corresponding MP2 results are shown in Table 11.4, where the A values refer to the change relative to the valence only MP2 with the same basis set. Essentially identical changes are found at the CCSD(T) level. 

Augmented with additional tight polarization functions Relativistic version of the cc-pVQZ basis Geometry = level at which the structure is optimized... 

The AO basis set should be of triple zeta or better quality polarization functions are important and additional basis functions with very tight and diffuse exponents are helpful. A good compromise between accuracy and cost is provided by the AO basis set given by Chipman [5], enlarged by an additional tight s function. 

Before discussing the data, a note on the cc basis sets used is needed. When the cc basis sets for third-row elements such as sulfur were first developed, the numbers of polarization functions used were the same as in the basis sets for the second-row elements (e.g.. Id for cc-pVDZ, 2dlf for cc-pVTZ, and so on). It was subsequently found that the d set for third-row elements was inadequate and needed to be expanded by adding a set of tight d functions. The resulting basis sets are referred to as cc-pV(X+d)Z and aug-cc-pV(X+d)Z. For H and second-row elements, these sets are the same as the original cc-pVXZ and aug-cc-pVXZ sets, but for third-row elements they have an extra set of d functions. 

ENaC is located in the apical membrane of polarized epithelial cells where it mediates Na+ transport across tight epithelia [3], The most important tight epithelia expressing ENaC include the distal nephron of the kidney, the respiratory epithelium, and the distal colon. The basic function of ENaC in polarized epithelial cells is to allow vectorial transcellular transport of Na+ ions. This transepithelial Na+ transport through a cell involves... 

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