The scope of problems treatable by ab initio wavefunction methods has expanded greatly through the application of local approximations. In particular, atomic orbital (AO) based wavefunction methods have emerged as powerful techniques for exploiting sparsity and have been applied to biomolecules as large as 1707 atoms [Maurer, S. A.; Lambrecht, D. S.; Flaig, D.; Ochsenfeld, C. J. Chem. Phys. 2012,  136, 144107]. Correlated wavefunction methods, however, converge notoriously slowly to the basis set limit and, excepting the use of large basis sets, will suffer from a severe basis set incompleteness error (BSIE). The use of larger basis sets is prohibitively expensive for AO basis methods since, for example, second-order M�ller-Plesset perturbation theory (MP2) scales linearly with the number of atoms, but still scales as O(N5) in the number of functions per atom. Explicitly correlated F12 methods have been shown to drastically reduce BSIE for even modestly sized basis sets. In this work, we therefore explore an atomic orbital based formulation of explicitly correlated MP2-F12 theory. We present a simple approach to the derivation of general AO basis methods, a discussion of the advantages and disadvantages of employing AO basis methods, and a preliminary investigation into the implementational difficulties associated with explicitly correlated AO basis methods and with AO basis methods in general. Particular emphasis is put on the challenges associated with the implementation of AO basis methods in a massively parallel context.

Explicitly correlated atomic orbital basis methods and their place in the future of quantum chemistry

246th National Meeting (2013)

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