Relativistic effects on NMR parameters

J. I. MELO; RUIZ DE AZUA M.C.; GIRIBET C; G.A. AUCAR; R. ROMERO

Kerkrade, The Netherlands,

Congreso; European Research Conference: "Electron correlation in a relativistic framework: advanced methods for calculations on heavy and superheavy elements"; 2001

European Science Foundation (ESF)

<!-- @page { size: 8.5in 11in; margin: 0.79in } P { margin-bottom: 0.08in } --> In the present work, relativistic corrections to magnetic molecular properties are derived from their relativistic RSPT(2)-like expression within Dirac-Fock space. In first place, the relativistic RSPT(2) expression is expanded up to order c-4 and reexpressed in terms of only those excited relativistic states which correspond to N-electron excited states in the non-relativistic limit, i.e. to the molecular Schrödinger Hamiltonian, HSCH. That expressions are then evaluated considering the no-pair approximation. To this end, expansion through order c-2 in the unperturbed molecular states is required, which in the no-pair approximation, can be readily obtained from H(2)=HSCH+D. The matrix elements between positive-energy four spinors corresponding to the relativistic magnetic perturbation are expanded up to order c-3 in order to derive an operator D*. This operator acting on the molecular states obtained from H(2) yields matrix elements of the perturbation which are correct to the same order. The final expressions are of second and third order within RSPT energy corrections to the Schrödinger molecular ground state in terms of operators D and D*.Relativistic corrections to both dia- and para-magnetic terms of nuclear magnetic shieldings are presented at RPA level of approach. As a model compound we used CH3X ( X=Br, I ). We get for the first time numerical results from Darwin and Mass-Velocity corrections to the diamagnetic terms. Correlation corrections for the main relativistic terms were calculated using the SOPPA approach. They are small for our model compounds. 1. G.A.Aucar and J. Oddershede, Int. J. Quantum Chem. 47, 425 ( 1993 ). 2. G. A. Aucar, T. Saue, L. Visscher, H.J.Jensen, J. Chem. Phys. 110, 6208 ( 1998 ). 3. G. A. Aucar, H. J. Jensen and J. Oddershede, Chem. Phys. Lett. 232, 47 ( 1995 ). 4. R. H. Romero and G. A. Aucar, Phys. Rev. A 57, 2212 ( 1998 ). 5. P. F. Provasi, S. P. A. Sauer and G. A. Aucar, J. Chem. Phys. 112, 6201 ( 2000 ). 6. "A QED-based approach to the indirect nuclear spin coupling tensor". R. H. Romero and G. A. Aucar, Phys. Rev. A. Submitted.