INVESTIGADORES
MALDONADO Alejandro Fabian
artículos
Título:
The appearance of an interval of energies that contain the whole diamagnetic contributions to NMR magnetic shieldings.
Autor/es:
ALEJANDRO F. MALDONADO; GUSTAVO A. AUCAR
Revista:
JOURNAL OF CHEMICAL PHYSICS
Editorial:
AMER INST PHYSICS
Referencias:
Lugar: Chicago; Año: 2007 vol. 127 p. 154115 - 154122
ISSN:
0021-9606
Resumen:
Working within relativistic polarization propagator approach it was shown in a previous article that the electronic origin of diamagnetic contributions to NMR nuclear magnetic shielding, $sigma^d$, mostly arise from excitations that fit in a well defined interval of energies such that $2mc^2$ $leqq$ $left ( varepsilon_{i} - varepsilon_{ar{s}} ight )$ < $4mc^2$. That interval of energies do not have in principle any physical reason to be so well defined, and giving a large amountof the total contribution to $sigma^d$, {it e.g.} close to 98 % of it. Then a further study is given in this article where we show some of the main characteristics of that interval of energy, like its bothuniversal appearance and basis set independence. Our main result is the finding that $sigma^d$ is completely described by that interval of excitation energies, {it i.e.} there is no contribution arising from outside of it. Most of the contributions belonging to that interval arise from virtual electronic energies larger than $-3mc^2$. For heavier atoms there are few contributions from states with virtual negative-energies smaller than $-3mc^2$. The model systems under study were: Noble gases; $X$H ($X$=Br, I, At); $XH_2$ ($X$=O, S, Se, Te, Po); $XH_3$ ($X$=N, P, As, Sb, Bi); $XH_4$ ($X$=Sn, Pb) and $SnXH_3$ ($X$=Br, I). The pattern of contributions of occupied MOs is also shown where the $1s_{1/2}$ is the most important for excitations ending in the bottom half part of the above mentioned interval. On the other side the contribution of the other occupied MOs are more important than that of $1s_{1/2}$ for the other part of such interval. We also show that $sigma^d$ is electron correlation independent within both relativistic and non relativistic domain. In the case of $sigma^p$ we find out a clear dependence of electron correlation effects with relativistic effects; which is of the order of 30 % for Pb in PbH_{4}.