scholarly journals Local Structure of Cationic Sites in Dehydrated Zeolites Inferred from 27Al Magic-Angle Spinning NMR and Density Functional Theory Calculations. A Study on Li-, Na-, and K-Chabazite

2016 ◽  
Vol 120 (26) ◽  
pp. 14216-14225 ◽  
Author(s):  
Petr Klein ◽  
Veronika Pashkova ◽  
Haunani M. Thomas ◽  
Sarah R. Whittleton ◽  
Jiri Brus ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Local Structure ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Functional Theory ◽  
Angle Spinning

scholarly journals Computational and Experimental 1H-NMR Study of Hydrated Mg-Based Minerals

Molecules ◽  
2020 ◽  
Vol 25 (4) ◽  
pp. 933 ◽  
Author(s):  
Eric G. Sorte ◽  
Jessica M. Rimsza ◽  
Todd M. Alam
Keyword(s):  
1H Nmr ◽  
Density Functional ◽  
Nmr Spectra ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Functional Theory ◽  
Nmr Study ◽  
1H Nuclear Magnetic Resonance ◽  
Angle Spinning ◽  
Periodic Calculations

Magnesium oxide (MgO) can convert to different magnesium-containing compounds depending on exposure and environmental conditions. Many MgO-based phases contain hydrated species allowing 1H-nuclear magnetic resonance (NMR) spectroscopy to be used in the characterization and quantification of proton-containing phases; however, surprisingly limited examples have been reported. Here, 1H-magic angle spinning (MAS) NMR spectra of select Mg-based minerals are presented and assigned. These experimental results are combined with computational NMR density functional theory (DFT) periodic calculations to calibrate the predicted chemical shielding results. This correlation is then used to predict the NMR shielding for a series of different MgO hydroxide, magnesium chloride hydrate, magnesium perchlorate, and magnesium cement compounds to aid in the future assignment of 1H-NMR spectra for complex Mg phases.

scholarly journals The ambient hydration of the aluminophosphate JDF-2 to AlPO-53(A): insights from NMR crystallography

2017 ◽  
Vol 73 (3) ◽  
pp. 191-201 ◽  
Author(s):  
Daniel M. Dawson ◽  
Richard I. Walton ◽  
Stephen Wimperis ◽  
Sharon E. Ashbrook
Keyword(s):  
Crystal Structure ◽  
Density Functional ◽  
Frictional Heating ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Good Representation ◽  
Functional Theory ◽  
Nmr Parameters ◽  
Nmr Crystallography ◽  
Angle Spinning

The aluminophosphate (AlPO) JDF-2 is prepared hydrothermally with methylammonium hydroxide (MAH+·HO−, MAH+ = CH3NH3 +), giving rise to a microporous AEN-type framework with occluded MAH+ cations and extra-framework (Al-bound) HO− anions. Despite the presence of these species within its pores, JDF-2 can hydrate upon exposure to atmospheric moisture to give AlPO-53(A), an isostructural material whose crystal structure contains one molecule of H2O per formula unit. This hydration can be reversed by mild heating (such as the frictional heating from magic angle spinning). Previous work has shown good agreement between the NMR parameters obtained experimentally and those calculated from the (optimized) crystal structure of JDF-2. However, several discrepancies are apparent between the experimental NMR parameters for AlPO-53(A) and those calculated from the (optimized) crystal structure (e.g. four 13C resonances are observed, rather than the expected two). The unexpected resonances appear and disappear reversibly with the respective addition and removal of H2O, so clearly arise from AlPO-53(A). We investigate the ambient hydration of JDF-2 using quantitative 31P MAS NMR to follow the transformation over the course of ∼3 months. The structures of JDF-2 and AlPO-53(A) are also investigated using a combination of multinuclear solid-state NMR spectroscopy to characterize the samples, and first-principles density functional theory (DFT) calculations to evaluate a range of possible structural models in terms of calculated NMR parameters and energetics. The published structure of JDF-2 is shown to be a good representation of the dehydrated material, but modification of the published structure of AlPO-53(A) is required to provide calculated NMR parameters that are in better agreement with experiment. This modification includes reorientation of all the MAH+ cations and partial occupancy of the H2O sites.

Is a Non-Transition Element Nitride Ferromagnet Ever Achievable? Indication of the N-N Pairing Instability

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1525-1531 ◽  
Author(s):  
Wojciech Grochala
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Transition Element ◽  
Density Functional Theory Calculations ◽  
Functional Theory

The enthalpy of four polymorphs of CaN has been scrutinized at 0 and 100 GPa using density functional theory calculations. It is shown that structures of diamagnetic calcium diazenide (Ca2N2) are preferred over the cubic ferromagnetic polymorph (CaN) postulated before, both at 0 and 100 GPa.

scholarly journals Tensor-structured algorithm for reduced-order scaling large-scale Kohn–Sham density functional theory calculations

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Chih-Chuen Lin ◽  
Phani Motamarri ◽  
Vikram Gavini
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Density Functional Theory Calculations ◽  
System Size ◽  
Real Space ◽  
Functional Theory ◽  
Reduced Order ◽  
Separable Approximation ◽  
Tensor Basis

AbstractWe present a tensor-structured algorithm for efficient large-scale density functional theory (DFT) calculations by constructing a Tucker tensor basis that is adapted to the Kohn–Sham Hamiltonian and localized in real-space. The proposed approach uses an additive separable approximation to the Kohn–Sham Hamiltonian and an L1 localization technique to generate the 1-D localized functions that constitute the Tucker tensor basis. Numerical results show that the resulting Tucker tensor basis exhibits exponential convergence in the ground-state energy with increasing Tucker rank. Further, the proposed tensor-structured algorithm demonstrated sub-quadratic scaling with system-size for both systems with and without a gap, and involving many thousands of atoms. This reduced-order scaling has also resulted in the proposed approach outperforming plane-wave DFT implementation for systems beyond 2000 electrons.

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