Analysis of the bond‐valence method for calculating ²⁹Si and ³¹P magnetic shielding in covalent network solids

Abstract

(29) Si and (31) P magnetic-shielding tensors in covalent network solids have been evaluated using periodic and cluster-based calculations. The cluster-based computational methodology employs pseudoatoms to reduce the net charge (resulting from missing co-ordination on the terminal atoms) through valence modification of terminal atoms using bond-valence theory (VMTA/BV). The magnetic-shielding tensors computed with the VMTA/BV method are compared to magnetic-shielding tensors determined with the periodic GIPAW approach. The cluster-based all-electron calculations agree with experiment better than the GIPAW calculations, particularly for predicting absolute magnetic shielding and for predicting chemical shifts. The performance of the DFT functionals CA-PZ, PW91, PBE, rPBE, PBEsol, WC, and PBE0 are assessed for the prediction of (29) Si and (31) P magnetic-shielding constants. Calculations using the hybrid functional PBE0, in combination with the VMTA/BV approach, result in excellent agreement with experiment. © 2016 Wiley Periodicals, Inc.

Spin–orbit effects on the 119Sn magnetic-shielding tensor in solids: a ZORA/DFT investigation

“…With the 4c relativistic DFT (with the BP86 functional), s ref is computed as 3199 ppm. [53][54][55]90 In contrast, the current results show that although PBE/GIPAW and cluster-based PBE/ ZORA/SC methods yield similar trends for tin(II)-containing and tin(IV)-containing solids, the two methods yield quite different results for s ref (Table 1). The underestimation of absolute shieldings predicted by ZORA calculations has been discussed previously.…”

“…37 Predicted isotropic 119 Sn chemical shifts in tin-containing solids calculated with plane-wave DFT techniques employing relativistic pseudopotentials at the ZORA level (without the SO component) are in good agreement with isotropic chemical shifts, although the calculated values do deviate by up to 200 ppm from experiment in some cases. 29,31,[46][47][48][49][50][51][52][53][54][55] The effect of hybrid functionals on computed magnetic shielding is also assessed. 16 In this study, we present calculations of the principal components of 119 Sn magneticshielding tensors for tin sites with different oxidation states and different co-ordination environments.…”

Calculations of solid‐state 43Ca NMR parameters: A comparison of periodic and cluster approaches and an evaluation of DFT functionals

“…Three clusters of CaCl 2 Á2H 2 O of increasing size are shown in Figure 2. Based on these observations, and those of earlier work, [26,[29][30][31] we used thirdco-ordination-shell clusters in all subsequent calculations because clusters of this size appear to conserve sufficiently the local point-group symmetry of the calcium sites. For both the 43 Ca magnetic-shielding and quadrupolarcoupling tensors, there are large differences between computed results for the first-and third-co-ordination-shell clusters, whereas the third-and fifth-co-ordination-shell clusters yield similar values.…”

“…GIPAW calculations used the following functionals: CA-PZ, [47,48] PW91, [49] PBE, [50] rPBE, [51] PBEsol, [52] and WC. [23,[25][26][27][28][29][30][31][32][33][54][55][56][57][58] In this work, clusters were constructed by expanding to the third co-ordination shell of atoms around the central 43 Ca site. [23,[25][26][27][28][29][30][31][32][33][54][55][56][57][58] In this work, clusters were constructed by expanding to the third co-ordination shell of atoms around the central 43 Ca site.…”

“…For example, the calculations presented in Ref. [23,[25][26][27][28][29][30][31][32][33] As Hartree-Fock exchange is difficult to implement in periodic calculations, we also illustrate the use of cluster models for calculating 43 Ca NMR parameters. [24] To the authors' knowledge, no systematic study has been undertaken to investigate model-chemistry effects on computed 43 Ca NMR parameters.…”