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Li P.,University of South Carolina | Parker T.M.,Center for Computational Molecular Science and Technology | Hwang J.,University of South Carolina | Deng F.,University of South Carolina | And 4 more authors.
Organic Letters | Year: 2014

CH-π interactions have been cited as an important contributor to carbohydrate recognition. To determine whether N-heterocycles form stronger CH-π interactions, the interactions of methyl ether groups with heterocyclic and nonheterocyclic aromatic surfaces were studied. Both experimental and computational experiments found that N-heterocyclic aromatic surfaces formed stronger interactions. This enhancement was attributed to attractive dipole-dipole interactions between the methyl ether C-O bond and the N-heterocyclic aromatic dipole. © 2014 American Chemical Society.

Parrish R.M.,Center for Computational Molecular Science and Technology | Sherrill C.D.,Center for Computational Molecular Science and Technology
Journal of Chemical Physics | Year: 2014

We develop a physically-motivated assignment of symmetry adapted perturbation theory for intermolecular interactions (SAPT) into atom-pairwise contributions (the A-SAPT partition). The basic precept of A-SAPT is that the many-body interaction energy components are computed normally under the formalism of SAPT, following which a spatially-localized two-body quasiparticle interaction is extracted from the many-body interaction terms. For electrostatics and induction source terms, the relevant quasiparticles are atoms, which are obtained in this work through the iterative stockholder analysis (ISA) procedure. For the exchange, induction response, and dispersion terms, the relevant quasiparticles are local occupied orbitals, which are obtained in this work through the Pipek-Mezey procedure. The local orbital atomic charges obtained from ISA additionally allow the terms involving local orbitals to be assigned in an atom-pairwise manner. Further summation over the atoms of one or the other monomer allows for a chemically intuitive visualization of the contribution of each atom and interaction component to the overall noncovalent interaction strength. Herein, we present the intuitive development and mathematical form for A-SAPT applied in the SAPT0 approximation (the A-SAPT0 partition). We also provide an efficient series of algorithms for the computation of the A-SAPT0 partition with essentially the same computational cost as the corresponding SAPT0 decomposition. We probe the sensitivity of the A-SAPT0 partition to the ISA grid and convergence parameter, orbital localization metric, and induction coupling treatment, and recommend a set of practical choices which closes the definition of the A-SAPT0 partition. We demonstrate the utility and computational tractability of the A-SAPT0 partition in the context of side-on cation-π interactions and the intercalation of DNA by proflavine. A-SAPT0 clearly shows the key processes in these complicated noncovalent interactions, in systems with up to 220 atoms and 2845 basis functions. © 2014 AIP Publishing LLC.

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