| Abstract
| - The refinement of borate structures using DFT calculations combined with experimental 11B quadrupolecoupling parameters from solid-state NMR spectroscopy is presented. The 11B electric field gradient (EFG)tensors, calculated using the WIEN2k software for trigonal and tetrahedral boron sites in a series of modelcompounds, exhibit a convincing linear correlation with the quadrupole coupling tensor elements, determinedfrom 11B MAS NMR spectra of the central or satellite transitions. The model compounds include Li2B4O7,Mg2B2O5, Mg3B2O6, NH4B(C6H5)4, and colemanite (CaB3O4(OH)3·H2O). The 11B quadrupole moment,Q = 0.0409 ± 0.0002 barn, derived from the linear correlation, is in excellent agreement with the acceptedvalue for Q(11B). This demonstrates that DFT (WIEN2k) calculations can provide precise 11B quadrupolecoupling parameters on an absolute scale. On the other hand, DFT calculations based on the reported crystalstructures for datolite (CaBSiO4(OH)) and danburite (CaB2Si2O8) cannot reproduce the experimental 11Bquadrupole coupling parameters to the same high precision. However, optimization of these structures byminimization of the forces between the atoms (obtained by DFT) results in a significant improvement betweenthe calculated and experimental 11B quadrupole coupling parameters, which indicates that reliable refinementsof the borate structures are obtained by this method. Finally, the DFT calculations also provide importantstructural information about the sign and orientation of the EFG tensor elements in the crystal frame, a kindof information that cannot be achieved from 11B NMR experiments on powdered samples.
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