Chapter 5
Effects of a Static Electric Field on Molecular Magnetic Properties Employing the CTOCD Method: Shielding Polarizabilities of CO, H O, andCH Compounds 2
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M. B. Ferrero , M . C. Caputo , and C. Ridruejo
Downloaded by CORNELL UNIV on May 14, 2012 | http://pubs.acs.org Publication Date: August 20, 1999 | doi: 10.1021/bk-1999-0732.ch005
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Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, 1428, Ciudad Universitaria, Buenos Aires, Argentina Consejo Nacional de Investigaciones Científicas y Técnicas, 1917 Rivadavia, Buenos Aires, Argentina
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A procedure based on formal annihilation of the diamagnetic contribution to the quantum mechanical election current density, via a continuos transformation of its origin all over the molecular domain, CTOCD-DZ method, is applied for determining shielding polarizabilities to first order in a perturbing electricfield.Analytical expressions for the third-rank tensors have been implemented in the SYSMO suite of programs employing the coupled Hartree-Fock (CHF) approach. In the limit of exact eigenfunctions to a model Hamihonian, the CTOCD-DZ expressions reduce to conventional terms. In any calculation relying on the algebraic approximation, irrespective of size and quality of the (gaugeless) basis set employed, all the components of the magnetic shielding polarizabilities evaluated within these methods are origin independent. Test calculations have been carried out in CO, H O andCH compounds. 2
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The presence of a time-independent electric field produces changes in the molecular second-rank tensors, i. e., the magnetic susceptibility χ«β and the magnetic shielding σ'φ of the 1th nucleus, which are the usual response properties to the presence of an external magnetic field. The contributions of Buckingham to the understanding of the behavior of molecular properties in the presence of electromagnetic fields are fundamental. The dependence of those properties on the electricfieldsis one of the topics in which his influence has been very important (1,2). The application of a static electric field polarizes the electronic charge distribution and leads to changes in molecular magnetic susceptibility and nuclear
© 1999 American Chemical Society
In Modeling NMR Chemical Shifts; Facelli, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1999.
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80 magnetic shielding, which can be rationalized in terms of response tensors of higher rank. In the presence of two external perturbations, i. e., the spatially uniform time-independent electric and magneticfieldsΕ and B, and of a permanent dipole moment μι, on nucleus I, the energy of the molecule, evaluated in the singlet electronic state |ψ ) is, employing Buckingham notation (7, 2) to denote molecular tensors, α
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W =W/ -MaEa-laa0E Efi+..... - JL ΧαβΕ Ββ + 2 2 -±ΧφΒ Β Εγ+ +ό
