Electron spin localisation and correlation effects for point defects in semi-ionic solids

Hydroxyl vacancies in single-walled aluminosilicate and aluminogermanate nanotubes

“…Both defects are magnetic, generating a doublet spin-state. In line with previous results for paramagnetic defects in zeolites [10], both for Al-Ge and Al-Si, the occupied (unoccupied) defect states (see Fig. 3 and SI) are highly localized around the undercoordinated Si (Ge) atom.…”

“…For completeness we considered the Al-Si (Al-Ge) 2D-sheets also by adopting the hybrid functional B3LYP [15] which is reported to account correctly for the chemical reactivity of aluminosilicate-based materials [20]. In line with previous HF-based calculations for zeolites, which produced band gaps considerably larger than PW91 results [10], the B3LYP band gaps are wider than both the PW91 values and the experimental optical gap of 3.6 eV [3]. Specifically, within the adopted triple-zeta basis (see SI), we found 9.3 eV and 7.42 eV for Al-Si and Al-Ge 2D-sheets respectively.…”

Effects of global orbital cutoff value and numerical basis set size on accuracies of theoretical atomization energies

“…While the numerical basis sets have been successfully employed in the studies of various phenomena [40][41][42][43][44], systematic studies on the size effect of basis sets are scarce. Altmann et al [45] evaluated the performance of numerical basis sets in DFT calculations on sulfur-containing molecules and another two groups testified the performance of DMol 3 with regard to electron affinities [40] and binding energies of hydrogen bonded complexes [33,46].…”

Hydroxyl vacancies in single-walled aluminosilicate and aluminogermanate nanotubes

“…Re-gardless of the specific route adopted for their synthesis, both Al-Si and Al-Ge tubes are achiral and analogous to zig-zag (n, 0) semiconducting carbon-based nanotubes [8]. Following a recent Density Functional Theory (DFT) study of Imogolite-based nanotubes [9], which opened up the possibility of first-principle studies for these systems, as well as previous simulations of neutral paramagnetic defects in zeolites [10] we address the effects of the simplest defects, i.e. neutral hydroxyl (-OH) vacancies, on Al-Ge and Al-Si in terms of both electronic structure changes and ensuing modifications in the global insulating properties.…”

“…For completeness we considered the Al-Si (Al-Ge) 2Dsheets also by adopting the hybrid functional B3LYP [15] which is reported to account correctly for the chemical reactivity of aluminosilicate-based materials [20]. In line with previous HF-based calculations for zeolites, which produced band gaps considerably larger than PW91 results [10], the B3LYP band gaps are wider than both the PW91 values and the experimental optical gap of 3.6 eV [3]. Specifically, within the adopted triple-zeta basis (see SI), we found 9.3 eV and 7.42 eV for Al-Si and Al-Ge 2D-sheets respectively.…”