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Simulation of high pressure diffraction patterns: details on calculations
Each time you change a parameter, the diffraction patterns are calculated as follow
- calculate the unit cell volume using pressure and a third order 3d order Birch-Murnagham equation of state.
- calculate unit cell parameters from the unit cell volume. In this procedure, we keep the axial ratios a/b, a/c and unit cell angles to their zero pressure values.
- calculate d-spacings for all (hkl) planes in the JCPDS card from the unit cell parameters,
- for each plane, calculate the diffraction angle 2theta from the d-spacings and experimental wavelength.
- for each active phase, calculate a synthetic diffraction spectrum assuming a gaussian peak profile with the peak width provided by the user. Intensities from the JCPDS card are scalled by the intensity factor provided by the user.
- plot the pattern.
- sort all reflections present in the pattern and put them in the reflection table.
- there are no temperature effects.
- axial ratios and unit cell angles are not pressure dependent.
- calculations for triclinic and rhombohedral remain to be implemented.
Include your own JCPDS card in the program
- If you want to send me your own cards, I will include them in the database. However, I have had bad experiences with user provided cards. Some of them are very sloppy and completely wrong. Therefore, if you send me a card, I want
- a full reference for your peak positions and intensities (JCPDC card, mincryst database...)
- a full reference for the equation of state.
- Those references and your name will be included in the card.
Sebastien Merkel, 02/2006