Magnetic properties in heavy-atom containing molecules

GUSTAVO A. AUCAR

Santiago de Chile

Congreso; WATOC; 2014

Comité internacional

The search for a QED-based (and then QFT-based) formalism that brings solid grounds to the whole area of relativistic quantum chemistry was just implicit in the first decades of the quantum theory. During the last few years it was shown that it is still unclear how to derive a well-defined N-electron relativistic Hamiltonian, and also the way negative-energy states may contribute to electron correlation. Furthermore, the relationship among electron correlation and radiative QED corrections is even more difficult to guess. These are few of the fundamental problems that need to be solved before such a program of research is finished within the wave function approach. The polarization propagator formalism [1, 2] was developed as an alternative approach to the study of atomic and molecular properties within both regimes, relativistic and non-relativistic, NR. Indeed, the relativistic polarization propagators gave new insights to the understanding of the physical origin of magnetic properties. As an example, diamagnetic and paramagnetic contributions, which arise from completely different electronic mechanisms within the NR regime are now unified within polarization propagators. They are produced by the same mechanism which is still not completely understood. One of its reasons is our ?NR way of thinking?. It is hardly seen how to grasp physical insights on magnetic properties without going down from 4-component to 2-component formalism, meaning the NR theoretical framework. In this communication I will shortly expose how far away one can go today working with relativistic polarization propagators [3], to get new insights on the electronic origin of atomic and molecular properties for heavy-atom containing molecules. Some of them are related with the following effects: nuclear size, electron correlation and QED. I will also show why paramagnetic contributions become diamagnetic in heavy elements and the relationship among spin-tensor operators and Kramers restricted or time reversal symmetric operators. I will focus on the treatment of NMR spectroscopic parameters within that formalism that is still not broadly used by the quantum chemistry community, perhaps for historical reasons. I will show results of shieldings and J-coupling calculations on heavy-atom containing molecules. Most of the other response properties can be treated in a similar manner.