Regularized SCAN functional

We propose modifications to the functional form of the Strongly Constrained and Appropriately Normed (SCAN) density functional to eliminate numerical instabilities. This is necessary to allow reliable, automatic generation of pseudopotentials (including projector augmented-wave potentials). The regularized SCAN is designed to match the original form very closely, and we show that its performance remains comparable

Tin chemical shift anisotropy in tin dioxide: on ambiguity of CSA asymmetry derived from MAS spectra

Two different axial symmetries of theandnbsp;119Snandnbsp;chemical shiftandnbsp;anisotropyandnbsp;(CSA) inandnbsp;tin dioxideandnbsp;with theandnbsp;asymmetryandnbsp;parameter (andeta;) of 0 and 0.27 were reported previously based on the analysis of MASandnbsp;NMR spectra. By analyzing the static powder pattern, we show that theandnbsp;119Sn CSA is axially symmetric. A nearly axial symmetry and the principal axis system of theandnbsp;119Sn chemical shift tensor in SnO2andnbsp;were deduced from periodic scalar-relativistic density functional theory (DFT) calculations of NMR parameters. The implications of fast small-angle motions on CSA parameters were also considered, which could potentially lead to a CSA symmetry in disagreement with aandnbsp;crystal symmetry. Our analysis of experimental spectra usingandnbsp;spectral simulationsandnbsp;and iterative fittings showed that MAS spectra recorded at relatively high frequencies do not show sufficiently distinct features in order to distinguish CSAs with andeta;andnbsp;andasymp;andnbsp;0 and andeta;andnbsp;andasymp;andnbsp;0.4. The example of SnO2andnbsp;shows that both the MASandnbsp;lineshapeandnbsp;and spinning sideband analyses may overestimate the andeta; value by as much as andsim;0.3 and andsim;0.4, respectively. The results confirm that a static powder pattern must be analysed in order to improve the accuracy of the CSA asymmetry measurements. The measurements on SnO2andnbsp;nanoparticlesandnbsp;showed that the asymmetry parameter of theandnbsp;119Sn CSA increases for nm-sized particles with a larger surface area compared to andmu;m-sized particles. The increase of the andeta; value for tin atoms near the surface in SnO2andnbsp;was also confirmed by DFT calculations.</p