title: Why benchmark-quality computations are needed to reproduce 1-adamantyl cation NMR chemical shifts accurately.
abstract: While the experimental (1)H NMR chemical shiftsof the 1-adamantyl cation can be computed within reasonably small error bounds, the usual Hartree-Fock and density functional quantum-chemical computations, as well as those based on rather elaborate second-order Møller-Plesset perturbation theory, fail to reproduce its experimental (13)C NMR chemical shifts satisfactorily. This also is true even if the NMR shielding calculations treat electron correlation adequately by the coupled-cluster singles and doubles model augmented by a perturbative correction for triple excitations (i.e., at the CCSD(T) level) with quadruple-ζ basis sets. We demonstrate that good agreement can be achieved if highly accurate 1-adamantyl cation equilibrium geometries based on parallel computations of CCSD(T) gradients are employed for the NMR shielding computations.
authors.affiliation: Institut für Physikalische Chemie, Universität Mainz, Jakob-Welder-Weg 11, D-55099 Mainz, Germany. harding@mail.utexas.edu
authors.forename: Michael E
authors.initials: ME
authors.lastname: Harding
authors.forename: Jürgen
authors.initials: J
authors.lastname: Gauss
authors.forename: Paul von Ragué
authors.initials: Pv
authors.lastname: Schleyer