The physics behind NMR spectroscopic parameters and new results from polarization propagators

GUSTAVO A. AUCAR

Beijing

Conferencia; REHE 2010 "Exact Relativistic Methods for Electronic Structure and Magnetic Property Calculations"; 2010

College of Chemistry and Molecular Engineering Peking University

Recent developments of formalisms which include relativistic effects within different theoretical frameworks and at different level of theory, for calculating NMR spectroscopic parameters J and σ, show that one can assess a large amount of data arising from heavy-atom containing molecules1. Still new challenges do appear and needs to be tackled, like what is the best way to include QED effects and electron correlation. The NR polarization propagator formalism was developed in the early 1970s by Jens Oddershede and coauthors. They are special devices from which one can get a deep understanding of the electronic mechanism which produce any response property like NMR spectroscopic parameters. From them reliable calculations of such parameters are obtained at the second-order level of approach. Since the early 1990s we have been involved in its relativistic and QED extensions2. From the beginning it was shown that one gets NR expressions from its corresponding relativistic generalizations by making c goes to infinity and the fact that time-reversal symmetry should be applied instead of the spin-symmetry within the relativistic framework. In this presentation we are going to sum up some of the new insights that arise from our formalism3: the interpretation of time-reversal symmetry applied to response properties, the unification of magnetic terms (the appearance of a unique electronic mechanism!) which replace the NR paramagnetic and diamagnetic contribution of J and σ, and the concept of virtual creation and destruction of electron-positron pairs (a fundamental concept for understanding response properties within the relativistic framework). We are going also to show new benchmark ab initio calculations of J and σ for molecules which contain more than two heavy atoms and the appearance of new effects.             References 1.   H. Fukui, Bull. Chem. Soc. Jpn. 83, 635 (2010); W. Liu, Molec. Phys. 108, 1679 (2010); J. Autschbach and S. Zheng, Annual Report on NMR Spect. 67, 1 (2009); T. Helgaker, M. Jaszunski and M. Pecul, Prog. in NMR Spect. 53, 249 (2008);  J. Vaara, Phys. Chem. Chem. Phys. 9, 5399 (2007). 2.   G. A. Aucar and J. Oddershede, Int. J. Quantum Chem. 47, 425 (1993); R. H. Romero and G. A. Aucar, Phys. Rev. A 65, 53411 (2002). 3.   G. A. Aucar, R. H. Romero and A. F. Maldonado, Int. Rev. Phys. Chem. 83, 1 (2010).