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Manuscript Title: Simulation of EPR-spectra of randomly oriented samples. See erratum Comp. Phys. Commun. 28(1982)217.
Authors: C. Daul, C.W. Schlapfer, B. Mohos, J. Ammeter, E. Gamp
Program title: POWDER
Catalogue identifier: ABVG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 21(1981)385
Programming language: Fortran.
Computer: CDC 6000.
Operating system: SCOPE 3.4.
RAM: 130K words
Word size: 8
Peripherals: disc, graph plotter.
Keywords: Crystallography, Anisotropic g-tensor, Anisotropic hyperfine Tensor, Anisotropic Perturbation calculation, Numerical integration And differentiation, Noise filter, Epr.
Classification: 8.

Nature of problem:
The EPR spectra of polycrystalline paramagnetic samples exhibits often complex features due to hyperfine and/or dipole-dipole and/or quadrupole interaction of the electronic and nuclear spins. This program calculates the first derivative of the EPR absorption spectrum of randomly oriented samples using the following approximations: i) the eigenvalues of the spin Hamiltonian are given by second order perturbation theory; ii) theintensities of the EPR transitions are determined by Zeeman interaction only; iii) the paramagnetic species are uniformly or randomly distributed in space. iv) 'allowed' transactions are calculated only.

Solution method:
The single crystal spectra for particular orientations are calculated. They are summed over all spacial orientations (Simpson rule) and convoluted with a line shape function giving the absorption line. A subsequent numerical derivation yields the 1st derivative spectrum and reduces the random derivations due to the limited number of orientations.

In the present version, the stick spectrum is convoluted with a line- shape function after the summation over all orientations has been carried out. This implies that only line widths independent upon orientation and mI can be treated. Furthermore, since a perturbation calculation is used, it is required that Eta(Zeeman) > Eta(hyperfine), Eta(Zeeman) > Eta(dipole-dipole) and that Eta(hyperfine) > Eta(quadrupole).

Running time:
Ranges between 10 s and 10 min on the CDC 6000.