
=================================   crystal   ================================


   Crystal calculates diffraction profiles of perfect crystals, and
   some imperfect crystals: curved crystals and mosaic crystals.

   It allows Bragg and Laue geometries and (in the case of perfect crystals)
   diffracted and transmitted intensity calculations.
   The diffracted intensity can be calculated as a function of either rock
   angle or photon energy.
   It uses XRAYLIB to define the crystal structure and to
   retrieve the scattering factors to build the crystal structure factors.



Reference:

Sanchez del Rio, M., Perez-Bocanegra, N., Shi, X., Honkimaki, V. & Zhang, L. (2015).
J. Appl. Cryst. 48, 477-491. http://dx.doi.org/10.1107/S1600576715002782
in free acces at:
https://arxiv.org/abs/1502.03059

Zachariasen, W. (1967). Theory of X-ray Diffraction in Crystals. New York: Dover



This is a description of the input parameters for crystal:
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CRYSTAL: Select a crystal from this list of crystals.

h MILLER INDEX: The h Miller index
k MILLER INDEX: The k Miller index
l MILLER INDEX: The l Miller index


TEMPERATURE FACTOR: Three possibilites:
       Enter the exp(-M) value (a positive value between 0 and 1)

MOSAIC CRYSTAL: Select YES when you want "mosaic crystal", otherwise
	"perfect crystal" is set.

CRYSTAL MODEL:
    Perfect crystal: Used the theory of Zachariasen
    Mosaic: Used modaic crystal model of Zachariasen
    Bent Crystal ML: uses Multilamellar model for curved crystals
    Bent Crystal PP: Used Penning-Polder model for LAUE (only working for
        Laue!!) curved crystals.

GEOMETRY: select one of the four cases combining Laue and Bragg cases
	for either diffracted or transmitted beam. Note that the
	transmitted intensity is not implemented for mosaic crystals.

SCAN: The scanned variable for the plot. Angular and Energy scans are
	allowed. The angular variable can be: Theta, when absolute angle
	is wanted; Th-ThBragg(corrected) or angular scan with zero at
	the bragg angle corrected for refraction; Th-ThBragg or angular
	scan with zero at the bragg angle; and y is dimensionless angular
	variable defined by (for instance) in the Zachariasen book.
	In the case of angular scans the unit can be set, except in the
	case of y. Energy is always in eV.

SCAN UNITS: angular units, if angular scan is set.

MIN SCAN VALUE: min value for the scanning variable.

MAX SCAN VALUE: max value for the scanning variable.

SCAN POINTS: the number of scanning points.

FIX VALUE (E[eV]) OR Theta[deg]): Place here either the energy value of the
	monochromatic incident photon beam (when angular scan is
	selected) or the grazing angle [in degrees] when a energy scan
	is wanted.
	In the case of energy scan, the program can calculate
	automatically the theta angle if one inputs the energy. If this
	option is selected, enter the Energy with a minus sign in this box.

ASYMMETRY ANGLE [deg]: the angle between the Bragg planes and the crystal
	surface. It is 0.0 for the symmetrical Bragg case and 90.0 for
	the symmetrical Laue case.
	This input is not present when using Mosaic crystals, which are
	always symmetrical.

CRYSTAL THICKNESS [cm]: the crystal thickness in cm

MOSAICITY [deg fwhm]: The mosaicirty of the mosaic crystal (if selected).

For bent crystal models (ML or PP) you also have:

R SAGITTAL [cm]: The radius of curvature in the sagittal direction (in
    direction perpendicular to the diffraction plane)

R MERIDIONAL [cm]: The radius of curvature in the meridional direction
    (in the diffraction plane)

ANYSOTROPY: Select ISOTROPIC OR ANYSOTROPIC MODEL. If ISOTROPIC define the
    Poisson ratio. If ANYSOTROPIC define the cutting directions, or the
    compliance tensor from an external file.



