REPULSION, A Novel Approach to Efficient Powder Averaging in Solid-State NMR
✍ Scribed by Mads Bak; Niels Chr Nielsen
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 277 KB
- Volume
- 125
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
A novel approach to efficient powder averaging in magnetic sphere. Because the computation time is proportional to the resonance is presented. The method relies on a simple numerical number of crystallite orientations and because high-quality procedure which based on a random set of crystallite orientations averaging corresponding to a uniform distribution of crysthrough simulation of fictive intercrystallite repulsive forces iteratallite orientations is critical for obtaining reliable parameters tively determines a set of orientations uniformly distributed over for anisotropic parts of the spin Hamiltonian, several studies the unit sphere. The so-called REPULSION partition scheme is have recently addressed methods for efficient powder avercompared to earlier methods with respect to the distribution of aging in magnetic resonance (1-5).
crystallite orientations, solid angles, and powder averaging effi-
A criterion for, in a minimum number of steps, achieving ciency. It is demonstrated that powder averaging using REPULacceptable powder averaging corresponding to a uniform SION converges faster than previous methods with respect to the distribution of crystallite orientations, is that each orientation number of crystallite orientations involved in the averaging. This feature renders REPULSION particularly attractive for calcula-through its weighting factor contributes equally to the sum tion of magic-angle-spinning solid-state NMR spectra using a minof contributions from all crystallites. Otherwise, expensive imum of crystallite orientations. For numerical simulation of powcomputing time is spent on crystallites only providing a der spectra, the reduced number of required crystallite orientations minor contribution to the spectrum. Since each weighting translates into shorter computation times and simulations less factor may be assumed proportional to the solid angle, this prone to systematic errors induced by finite sets of nonuniformly criterion may be regarded equivalent to finding the most distributed crystallite orientations. ᭧ 1997 Academic Press uniform distribution of crystallite orientations over the unit sphere. Despite numerous studies it has not, to our knowledge, been demonstrated possible to derive a set of truly 132