
 =================================   f1f2      ============================

 f1f2 calculates Elastic Anomalous Photon-Atom Scattering, and their derived
 parameters (refraction index, photoelectric absorption, reflectivity).

 ** VERY IMPORTANT **

 PLEASE NOTE THAT F1F2 APPLICATION DOES NOT INCLUDE COMPTON SCATTERING
 CALCULATIONS. IF FOR YOUR CALCULATIONS COMPTON IS IMPORTANT, PLEASE
 USE CROSSSEC OR POWER APPLICATIONS.
 THIS AFFECTS THE VALUES: BETA, MU, CROSS SECTION AND DELTA/BETA


		Practical tip: 

		For cross section, scattering factors and reflectivity, use
		    f1f2 and try to define your material in molecular
		    form.

		For calculating attenuation coefficients, beta and cross
                   sections use CrossSec (and not f1f2) because:
		    i) it is more accurate in case of defining the material
			by its weight fractions.
		    ii) it used all channels in the attenuation (contrary to 
		        f1f2 that only uses photoelectron cross section).


 The data are taken from the XRAYLIB data base.

 Possible calculations:
	       f1
	       f2
	       delta [n=1-delta-i beta]
	       betaPh [n=1-delta-i beta, betaPh is the Photoelectric component]
	       Photoelectric linear abs coeff (mu [cm^-1)]
	       Photoelectric mass  abs coeff (mu [cm^2/g)]
	       Photoelectric Cross Section [barns]
	       s-pol reflectivity
	       p-pol reflectivity
	       unpolarized reflectivity
              delta/betaPh (delta/beta from Photoelectric interaction only)



    Calculation method (for compounds)
    ==================================


	i) calculate the scattering factors f1_i and f2_i for each elements by
	   calling f1f2_calc
	ii) Calculate the atomic composition f_i of each element in the
	   compound
	iii) The mean scattering factors for the compound are the
	   averaged scattering factors from the elements (f_i):
		f1 = Sum{ f_i * f1_i }  (similarly for f2)

	The MW (molecular weight) is MW = Sum { f_i * Ai), being Ai
		the atomic weight of the i-th element available in
		the molecule (compound) formula.



		Practical tip:

		For cross section, scattering factors and reflectivity, use
		    f1f2 and try to define your material in molecular
		    form.
		For calculating attenuation coefficients, use CrossSec
		    (and not f1f2) because:
		    i) it is more accurate in case of defining the material
			by its weight fractions.
		    ii) it used all channels in the attenuation (contrary to
		        f1f2 that only uses photoelectron cross section).


    3) Description of the input parameters
    ======================================
material: Select the desired material type. Three options are available:
	a) Element(formula) calculation for a single element.
	b) Compounds(formula) calculation for a compound. The user
		defines the compound formula.
		The syntaxis is the following: string with the chemical
		formula of the compound.
		Examples:
		H20
		SiO2
	c) Compounds(by name) from the NIST list of compounds.


formula: The element or compound formula, depending the "material"
		selection.

density: The compound density in the case that option b) has been
		selected.

calculate: select the calculation magnitude. The "all" option is also
	available, and in this case all datasets are used (useful for
	comparisons). The "all" option here is incompatible with the
	"all" option in the "datasets" entry.


Energy [eV] grid: the abscissas values for the calculations. Two
		options are available:
		a) Standard
		b) User-defined, with the parameters described below.
		c) Single-value, with the energy to be entered in
		   "Starting Energy [eV]" box.

Stating Energy [eV]: the initial energy value (only available if either
		b) or c) is chosen in the "Energy [eV] grid" entry.

To: the last energy value (only available if b) is chosen in the
		"Energy [eV] grid" entry.

Number of points: the number of energy points (only available if b) is
		chosen in the "sin_theta/lambda grid" entry.

Grazing angle: the surface grazing angle (only available when
		"reflectivity" calculations are set in "Calculate" entry.
		Two options are available:
		a) Single-value, for calculations of Reflectivity versus
		   energy.
		b) User-defined, for calculations of Reflectivity versus
		   angle, or reflectivity versus both angle and energy
		   (2D plot).

Roughness rms [A]: The surface RMS roughness (only available when
		"reflectivity" calculations are set in "Calculate" entry.

Stating Graz angle [mrad]: the grazing angle (when single-value is set) or
		the initial grazing angle value (only available for
		reflectivity calculations).

To: the last grazing angle value (only available if both b) is chosen in the
		"Grazing angle" entry and for reflectivity calculations).

Number of angular points: the number of angle points (only available if both
		b) is chosen in the "Grazing angle" entry and for reflectivity
		calculations).

