Polarization propagators: a powerful tool for both reliable calculations and the analysis of NMR spectroscopic parameters on heavy and non-heavy atom containing molecules

ALEJANDRO MALDONADO; GUSTAVO A. AUCAR

Helsinki

Congreso; International Congress of Quantum Chemistry, 13 ICQC; 2009

Propagators are powerful theoretical tools that were first developed within the nonrelativistic regime and applied to calculate atomic and molecular properties more than 30 years ago. Recent relativistic generalization of polarization propagators has shown that they play a special role in describing the quantum origin of some molecular properties and the broad implication of their general definition.1 The theory of polarization propagators have: i) A formal definition that is the same for both the NR and relativistic regime; ii) This definition can be related with the scattering amplitude of QED; iii) Formal solutions of its equation of motion can be expressed in a perturbational scheme so that they may be improved in a well-defined way; iv) Several implementations at different levels of approach. Within the NR regime SOPPA and SOPPA-CC calculations are between the most reliables.2,3 Within the relativistic regime there appears several new understandings on the electronic origin of magnetic properties. As an example, diamagnetism arise as a NR approximation. When working within the relativistic regime one should be very careful in using well established NR physical concepts like dia- and para- magnetic contributions. In this presentation starting from a QED-based formulation of NMR spectroscopic parameters (that gives solid grounds to the relativistic polarization propagator theory), we will show recent calculations of such parameters for one, two- and more than two-heavy atom containing molecules. We show that we only need to apply the UKB prescription with small enough basis sets to get converged results of magnetic shieldings. In the case of J-couplings we show that relativistic effects and correlation effects contribute with opposite sign; in the case of HBr and HI systems both effects are of simmilar magnitud. 1. G. A. Aucar, Understanding NMR-J couplings by the theory of polarization propagators, Concepts in Magn. Reson. Part A 32A, 88, 2008. 2. J. E. del Bene, I. Alkorta and J. Elguero, A systematic comparison of SOPPA and EOM-CC J-couplings..., J. Chem. Theory and Comput. 4, 967, 2008. 3. T. Helgaker, M. Jaszunski and M. Pecul, The quantum-chemical calculations of NMR Jcouplings. Prog. in NMR Spectrosc. 53, 249, 2008.