The calculation of NMR shielding tensors based on density functional theory and the frozen-core approximation

Abstract

rnThe application of the frozen-core approximation to the calculation of the shielding tensor of nuclear magnetic resonance (NMR) spectroscopy is discussed and an implementation is presented. A complete formulation of the shielding calculation within the frozen-core approximation is given, both in general t e r m and for the special case of density functional theory (DFT) and "gauge including atomic orbitals" (GIAOs). The practical implementation is validated by a detailed discussion of the consequences of the approximation. The general conclusion is drawn that the frozen-core approximation is a useful tool for shielding calculations-if the valence space is increased to contain at least the ns, np, ( n -l)p, ( n -l ) d (fourth period and higher) shells, where n is the number of the given period in the periodic table of elements. The new method is applied to nSe shieldings and chemical shifts for a small number of compounds. The agreement between theory and experiment is good for relative shifts, whereas calculated absolute shieldings are generally too small by about 300-400 ppm. This difference is attributed to the relativistic contraction of the core density at the selenium atom that had been explicitly incorporated into the experimental absolute shielding scale. 0 1996 John Wiley & Sons, Inc.of chemistry and beyond. The range of nuclei that can be studied by NMR is steadily increasing. Thus, the area of multinuclear NMR, i.e., the study of nuclei other than--say-',*H, I3C, l4,I5N, I9F, 31 P, or 33S, is rapidly gaining importance [ll.The theoretical prediction of shielding tensors has a long and successful history. These calculations are carefully reviewed annually [21. A good

Revisiting HgCl2: A solution- and solid-state 199Hg NMR and ZORA–DFT computational study

“…Relativistic spin-orbit calculations using the zeroth-order regular approximation combined with density functional theory (ZORA-DFT) were performed using the Amsterdam Density Functional (ADF) program package [27] and its associated NMR program module [28][29][30][31]. The module DIRAC was applied to generate the core potentials for all atom types.…”

Hypo-electronic triple-decker sandwich complexes: synthesis and structural characterization of [(Cp*Mo)2{μ–η6:η6-B4H4E-Ru(CO)3}] (E = S, Se, Te or Ru(CO)3 and Cp* = η5-C5Me5)

“…Computation of the NMR shielding tensors employed gauge-including atomic orbitals (GIAOs), [43][44][45] using the implementation of Schreckenbach, Wolff, Ziegler, and coworkers. [46][47][48][49][50] . …”

Calculation of EPR g‐Tensors with Density Functional Theory

“…A cautionary note applies to elements with large semi-cores [71]. In this case, an adequate description of the core polarization is essential for obtaining reliable results.…”