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Manuscript Title: POWDERSPEC: a program for efficient simulation of isotropic EPR spectra.
Authors: V. Beltran-Lopez, L. Gonzalez-Tovany
Program title: POWDERSPEC
Catalogue identifier: ACGX_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 69(1992)397
Programming language: Fortran.
Computer: CYBER-180-830.
Operating system: NOS, DOS 3.0 or higher.
Peripherals: graph plotter.
Keywords: Powder pattern, Powder EPR spectra, Isotropic EPR, Spectra, Orthorhombic symmetry, Gaussian numerical Integration, Crystallography.
Classification: 8.

Nature of problem:
The interpretation of electron paramagnetic resonance (EPR) spectra of randomly oriented paramagnetic ions is a difficult problem because the random orientation of the crystallites dilutes the spectral features dependent on the angular position. The main features in these spectra can be predicted from the corresponding absorption functions or powder patterns. It is important, then, to have an accurate knowledge of these powder patterns for a reliable interpretation of the spectra. The program POWDERSPEC calculates in a fast and precise form the powder patterns and the corresponding spectra for the full range of the orthorhombic field parameter lambda, 0<= lambda <= 1/3, under the following conditions:
i) the paramagnetic ions are isotropically oriented.
ii) the values of the resonance magnetic field are given by second order perturbation theory.

Solution method:
This program generates the powder patterns of polycrystalline samples by means of the Gaussian numerical quadrature of the single-variable integral appearing in a general method for analytical calculation of these patterns. For obtaining the corresponding magnetic resonance spectra, the powder patterns are numerically convoluted using the mid- point approximation with a first-derivative Lorentzian or Gaussian lineshape of convenient width.

Since a perturbation calculation is used, it is required that the magnitude of H(Zeeman) > H(hyperfine) and H(Zeeman) > H(crystalline field). It is also assumed that the tensors g and A are isotropic. The convolution is made with the derivative of a lineshape function with constant width; i.e., only samples where the line width is independent of orientation can be treated.

Running time:
In the CYBER-180-830: 35 CPU seconds. In the IBM-PC/AT with numeric processor: 200 CPU seconds.