REPULSION, A NOVEL-APPROACH TO EFFICIENT POWDER AVERAGING IN SOLID-STATE NMR

A novel approach to efficient powder averaging in magnetic resonance i s presented. The method relies on a simple numerical procedure which b ased on a random set of crystallite orientations through simulation of fictive intercrystallite repulsive forces iteratively determines a se t of orientations uniformly distributed over the unit sphere. The so-c alled REPULSION partition scheme is compared to earlier methods with r espect to the distribution of crystallite orientations, solid angles, and powder averaging efficiency. It is demonstrated that powder averag ing using REPULSION converges faster than previous methods with respec t to the number of crystallite orientations involved in the averaging. This feature renders REPULSION particularly attractive for calculatio n of magic-angle-spinning solid-state NMR spectra using a minimum of c rystallite orientations. For numerical simulation of powder spectra, t he reduced number of required crystallite orientations translates into shorter computation times and simulations less prone to systematic er rors induced by finite sets of nonuniformly distributed crystallite or ientations. (C) 1997 Academic Press.