AN EFFICIENT METHOD FOR CALCULATING POWDER PATTERNS

A novel approach to the calculation of powder lineshapes is presented, Lineshapes from asymmetric second-rank tensor interactions are produc ed by summing lineshapes from symmetric tensors. This approach signifi cantly reduces the calculation time, greatly facilitating iterative no nlinear least-squares fitting of experimental spectra. Results are rep orted for anisotropic C-13 NMR lineshapes of glycine, benzoic acid, an d octanoic acid in a urea inclusion compound. Lineshapes from nonunifo rm distributions of crystallite orientations can also be calculated by using distributions of the Euler angles that define the orientation o f the principal-axis system of the chemical-shielding tensor with resp ect to the magnetic field. (C) 1996 Academic Press, Inc.