Quasiatomic orbitals (QUAOs) [1-2] are very effective for charge decomposition in molecules. They resemble spherically averaged atomic orbitals but are slightly deformed to accommodate polarization effects. The QUAO space contains the full SCF (Hartree-Fock or DFT) occupied space. QUAO-based Mulliken or L�wdin atomic populations, unlike their conventional counterparts, yield stable atomic populations which conform to chemical intuition, even for large basis sets and system sizes. Pipek-Mezey localization based on PAOs is also very stable. We explore the application of these localized occupied orbitals in our Coupled Cluster program, particularly for the expensive perturbational triple substitution (T) contributions. The Laplace transformation method enables the use of the simple canonical formulas for localized orbitals, greatly improving the scaling behavior for large systems. Our local virtual spaces consist of sets of Natural Correlation Orbitals, optimized separately for each localized occupied orbital. A further advantage of QUAOs is that they provide a set of valence virtual orbitals, allowing the decomposition of correlation energy to a strongly structure-dependent molecular valence contribution, and largely atomic (often Rydberg-type) contributions.[1] Lu et al. J. Chem. Phys. 2003, 120, 2629�2637[2] West et al. J. Chem. Phys. 2013, 139, 234107.

Localized Laplace transformed coupled cluster perturbative triples correction in quasiatomic orbitals

248th National Meeting (2014)

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