Calculated using coupled-cluster CCSD

Harmonic and cubic force fields of Sis were calculated using coupled-cluster (CC) theory (25) and a correlation-consistent basis set. Specifically, the CC singles and doubles (CCSD) method (24) was used in conjunction with the cc-pVTZ basis set (25) developed by Dunning and co-workers. The force... 

One can avoid these problems by using Coupled Cluster (CC) theory107, which contains infinite-order effects and therefore does not lead to the oscillatory behaviour of properties calculated with MPn108. Homoaromatic stabilization energies have been calculated for smaller molecules with CCSD(T) or QCISD(T)54 56. These are CC methods, which cover S and D excitations and, in addition, include T effects in a perturbational way109110. They represent some of the most accurate single determinant ab initio methods available today that can be applied in a routine way. 

There have been many calculations of a for neon itself at various levels of approximation. Some of these are summarized in Ref. [26] and a basis set analysis has been made in Ref. [25]. Of the electron-correlated results[42]-[47], there appears to be a consensus that the best value using coupled-cluster-single-doubles wavefunctions with a perturbational estimate of connected triplet excitations, CCSD(T), is 2.680-2.690 au[25],[44],[46],[47]. 

At the B3LYP/6-31 l-b- -G(d,p) -b ZPE level of theory, the local PAs of phenol at different sites are evaluated in kJmoL as follows 820 for para-C, 809 for ortho-C2, 757 for meta-Cs, 699 for ipso-C and 743 for oxygen . The coupled-cluster CCSD(T) approach in conjunction with the 6-311-1— -G(d,p) basis set yields a PA(C4) of 819 kJmol . When using an appropriate basis set, the calculated PAs thus compare reasonably well with the experimental value quoted above. 

In order to obtain more accurate energetic values, the electronic energies of the global minima are calculated using the coupled-cluster CCSD(T) theory at the complete basis set limit (CBS) for the small sizes of n = 2-8, and the composite G3B3 technique for all B[J clusters considered (with n — 2 20). Geometrical parameters are also fully optimized at the coupled-cluster CCSD(T) theory for... 

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