Electron-pair Approximation and Related Methods

Coupled Electron-pair Approximation and Related Methods 

The methods discussed so far require a computational time proportional to where n is the number of basis functions used. To go up one level to more sophisticated methods, Cl, CEPA or higher-order MBPT, increases the computation time to an dependence. It is therefore not surprising that few studies at this level on larger van der Waals molecules have appeared, e.g. (H20)2 - Ne-Na , N -HF, CO-HF, HCN- 

HF Ar-HCpo°, (AH )2 complexes (A = N,0,F,P,S,Cl)i and He-Oj . We may expect many more calculations at this level in the near future, as computers become rapidly more powerful. 

Effect of size-consistency corrections on the interaction energy. 

The effect of size-consistency corrections on the van der Waals well depth is quite pronounced if no dimer SCF precedes the Cl-type calculation, but not negligible otherwise even in (HjOfj (Table II). Considering that (H20)2 is among the more strongly bound van der Waals complexes, the relative influence on weaker complexes will be much more serious. 

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C. Coupled Electron-pair Approximation and Related Methods... 

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