INVESTIGADORES
AUCAR Gustavo Adolfo
congresos y reuniones científicas
Título:
Polarization propagators: a powerful tool for both reliable calculations and the analysis of NMR spectroscopic parameters on heavy and non-heavy atom containing molecules
Autor/es:
ALEJANDRO MALDONADO; GUSTAVO A. AUCAR
Lugar:
Helsinki
Reunión:
Congreso; International Congress of Quantum Chemistry, 13 ICQC; 2009
Resumen:
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.