INVESTIGADORES
MALDONADO alejandro Fabian
artículos
Título:
Relativistic effects on the nuclear magnetic shieldings of rare-gas atoms and halogen in hydrogen halides within relativistic polarization propagator theory.
Autor/es:
SERGIO S. GÓMEZ; ALEJANDRO F. MALDONADO; GUSTAVO A. AUCAR
Revista:
JOURNAL OF CHEMICAL PHYSICS
Editorial:
AMER INST PHYSICS
Referencias:
Lugar: Chicago; Año: 2005 vol. 123 p. 214108 - 214114
ISSN:
0021-9606
Resumen:
In this work an analysis of the electronic origin of relativistic effects on the isotropic dia- and paramagnetic contributions to the nuclear magnetic shielding $sigma(X)$ for noble gases and heavy atoms of hydrogen halides is presented. All results were obtained within 4-component polarization propagator formalism at different level of approach (RPA and PZOA), by using a local version of DIRAC code. From the fact that calculations of diamagnetic contributions to $sigma$ within RPA and PZOA approachs for HX (X = Br, I, At) and rare gas atoms are quite close each other and the finding that the diamagnetic part of the principal propagator at PZOA level can be developed as a serie (S($Delta$)), it was found that there are a branch of negative energy "virtual" excitations that contribute with more than 98 % of the total diamagnetic value even for the heavier elements, namely Xe, Rn, I and At. It contain "virtual" negative energy molecular orbital states with energies between $-2mc^2$ and $-4mc^2$. This fact can explain the excellent performance of the LR-ESC scheme for elements up to the fifth row in the Periodic Table. An analysis of convergency of S($Delta$) and its physical implications is given. It is also shown that the total contribution to relativistic effects of the innermost orbital ($1s_{1/2}$) is by far the largest. For the paramagnetic contributions results at RPA and PZOA approximations are similar only for rare gas atoms. On the other hand, if the Mass-correction contributions to $sigma^p$ are expressed in term of atomic orbitals a different pattern is found for 1$s_{1/2}$ orbitals contributions compared with all other s-type orbitals when the whole set of rare gas atoms are considered.