Journal of Physical Chemistry, Vol.99, No.12, 4000-4007, 1995
Ab-Initio Computation of Se-77 NMR Chemical-Shifts with the Iglo-SCF, the Giao-SCF, and the Giao-Mp2 Methods
Ab initio geometries and Se NMR chemical shifts have been computed for Me(2)Se, H2Se, MeHSe, EtSeH, Se(SiH3)2, SeF4, SeF6, SeOF2, H2CSe, Me(2)CSe, SeCO, CSe2, and selenophene (C4H4Se). The mean absolute deviations from experimental delta(Se-77) data are 97, 76, and 78 ppm at the IGLO-SCF/II/Expt., GIAO-SCF, and GIAO-MP2/962+(d)/MP2/962(d) levels, respectively, over a range of 2800 ppm. For selenium chemical shift calculations, diffuse functions have to be included in the basis set in order to describe the Se long pairs properly, which provide the largest localized valence MO contributions to each Se shielding. A delta(Se-77) value of ca. -40 ppm is predicted for gaseous EtSeH. Both SCF and MP2 methods fail to reproduce the delta(Se-77) chemical shift of Se-4(2+) which requires a multireference description.
Keywords:DENSITY FUNCTIONAL THEORY;GAUSSIAN BASIS FUNCTIONS;COUPLED HARTREE-FOCK;ATOMIC BASIS SETS;FIRST-ROW ATOMS;LOCALIZED QUANTITIES;MOLECULAR CALCULATIONS;SHIELDING CONSTANTS;MAGNETIC-SUSCEPTIBILITIES;ABINITIO