**POWDER.EXE**
program is intended for a simulation of powder EPR spectra.

It calculates resonance magnetic fields, their intensities and level numbers of allowed
transitions for some directions with the help of spiral circling of polar and
azimuthal angles.

For the estimation of resonance fileds the program imitates a sweeping of constant
magnetic field from Hmin to Hmax. Near resonance it uses small field steps with cubic
interpolation of energy level dependencies on magnetic field, far from resonance it
increases this step .

The program uses the exact numerical diagonalization of Spin-Hamiltonian matrix. It
draws on the screen and puts into output file (<*.GRV>) the spiral angular
dependencies of resonance magnetic fields and transition intensities. Then it integrates
these dependencies with Gaussian or Lorentzian (0-th, 1-st and 2-nd order derivatives) and
draws calculated powder spectrum on the screen. Simulated spectrum are saved in two ASCII
files:

1. <*.SPY> - file of one column with intensity values (Y-column); values of current
magnetic fields (X-column) are easily reconstructed for constant steps.

2. <*.PAR> - file with spectrum parameters: microwave frequency, minimal and maximal
values of X, number of steps (resolution) and so on.

With the help of **Powder.exe** you can prepare an atlas of simulated
spectra with different shape and width of individual EPR line, with different parameters
of spin-Hamiltonian, with different temperature.

Then you can compare calculated and observed spectra with the help of View_Spc.

Once calculated spiral angular dependencies can be re-read and used for new spectrum simulation with other individual line characteristics.

The program need such input data: the parameters of Zeeman interactions HS and HS3,
Crystal Field (CF) and hyperfine interactions SI in Spin-Hamiltonian, microwave
frequency and some others.

There are special entry program - FldEntry - that help
to make ready necessary input data with all conveniences.

Revised: April 17, 2010.