If accurate results are desired in quantum chemistry, the coupled-cluster (CC) approach is the method of choice. The accuracy provided by the most successful CC approach, the CC singles, doubles, and perturbative triples [CCSD(T)] method, is adequate for most chemical applications, and it is often referred to as the “gold standard” of quantum chemistry. Besides the level of correlation, the other factor seriously limiting the accuracy of computational results is the quality of the atomic orbital basis set. Large basis sets including functions of high angular momentum are required to reduce the error stemming from the incompleteness of the basis below an acceptable magnitude. A partial solution to this problem is offered by explicitly correlated approaches, which are based on wave functions that explicitly contain the interelectronic distances thereby significantly reducing the basis set requirements. Unfortunately, calculations with explicitly correlated CCSD(T) are still relatively time consuming. Recently, we have developed a reduced-cost explicitly correlated CCSD(T) approach that is as accurate as the parent method. The approach is based on well-established data compression techniques, which were also successfully utilized to speed up conventional CC methods. The approach significantly extends the scope of explicitly correlated CCSD(T) and enables the accurate solution of the electronic Schrödinger equation for a couple of dozens of atoms.

 

 

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