new option for neutron scattering lengths

functions_crystallography.py
 - added option for neutron scattering lengths from Sears 1995
  - 'neutron_isotope_scattering_lengths_sears.dat'

 tests
  - Tests now pass as comparison of neutron structure factors with Vesta is now identical
  - additional tests for functionality added

Author: DanPorter

Dans_Diffraction/__init__.py

@@ -31,8 +31,8 @@
 Diamond
 2017
 
-Version 3.3.1
-Last updated: 08/11/2024
+Version 3.3.2
+Last updated: 20/11/2024
 
 Version History:
 02/03/18 1.0    Version History started.
@@ -82,6 +82,7 @@
 25/09/24 3.2.4  Fixed error of missing rotation matrices after load_spacegroup. Thanks asteppke!
 26/09/24 3.3.0  Added complex neutron scattering lengths for isotopes from package periodictable. Thanks thamnos!
 06/11/24 3.3.1  Fixed incorrect cell basis for triclinic cells. Added functions_lattice.py and tests. Thanks LeeRichter!
+20/11/24 3.3.2  Added alternate option for neutron scattering lengths
 
 Acknoledgements:
     2018        Thanks to Hepesu for help with Python3 support and ideas about breaking up calculations
@@ -162,8 +163,8 @@
            'Structures', 'Fdmnes', 'FdmnesAnalysis']
 
 
-__version__ = '3.3.1'
-__date__ = '2024/11/08'
+__version__ = '3.3.2'
+__date__ = '2024/11/20'
 
 
 # Build

Dans_Diffraction/classes_scattering.py

@@ -104,6 +104,9 @@ class Scattering:
     # Uses the coefficients for analytical approximation to the scattering factors from:
     #        "Waasmaier and Kirfel, Acta Cryst. (1995) A51, 416-431"
     _use_waaskirf_scattering_factor = False
+
+    # Use the neutron scattering factors from the Internation tables (Sears 1995)
+    _use_sears_scattering_lengths = False
 
     # Thermal Factors
     _use_isotropic_thermal_factor = True
@@ -161,6 +164,8 @@ def __str__(self):
         out += '      max twotheta: %s\n' % self._scattering_max_twotheta
         out += ' ---X-Ray Settings---\n'
         out += ' Waasmaier scattering factor: %s\n' % self._use_waaskirf_scattering_factor
+        out += ' ---Neutron Settings---\n'
+        out += ' Sears (ITC) scattering lengths: %s\n' % self._use_sears_scattering_lengths
         out += ' ---Magnetic Settings---\n'
         out += '   Mag. scattering: %s\n' % self._calclate_magnetic_component
         out += '  Mag. form factor: %s\n' % self._use_magnetic_form_factor
@@ -185,7 +190,7 @@ def setup_scatter(self, scattering_type=None, energy_kev=None, wavelength_a=None
                       powder_units=None, powder_pixels=None, powder_lorentz=None, powder_overlap=None,
                       specular=None, parallel=None, theta_offset=None,
                       min_theta=None, max_theta=None, min_twotheta=None, max_twotheta=None,
-                      output=True, scattering_factors=None, magnetic_formfactor=None,
+                      output=True, scattering_factors=None, scattering_lengths=None, magnetic_formfactor=None,
                       polarisation=None, polarisation_vector=None, azimuthal_reference=None, azimuth=None, flm=None):
         """
         Simple way to set scattering parameters, each parameter is internal to xtl (self)
@@ -205,6 +210,7 @@ def setup_scatter(self, scattering_type=None, energy_kev=None, wavelength_a=None
         specular    : self._scattering_specular_direction : [h,k,l] : reflections normal to sample surface
         parallel    : self._scattering_parallel_direction : [h,k,l] : reflections normal to sample surface
         scattering_factors: self._use_waaskirf_scattering_factor : xray scattering factor ['waaskirf', 'itc']
+        scattering_lengths: self._use_sears_scattering_lengths : neutron scattering lengths ['sears', 'default']
         magnetic_formfactor: self._use_magnetic_form_factor: True/False magnetic form factor for magnetic SF
         polarisation: self._polarisation                  : beam polarisation setting ['ss', 'sp'*, 'sp', 'pp']
         polarisation_vector: _polarisation_vector_incident: [x,y,z] incident polarisation vector
@@ -263,6 +269,14 @@ def setup_scatter(self, scattering_type=None, energy_kev=None, wavelength_a=None
                 print('Using scattering factors from: International Tables of Crystallography Vol. C, Table 6.1.1.4')
                 self._use_waaskirf_scattering_factor = False
 
+        if scattering_lengths is not None:
+            if scattering_lengths.lower() in ['sears', 'itc', 'alternate', 'alt']:
+                print('Using scattering lengths from International Tables of Crystallography Vol. C, Table 4.4.4.1')
+                self._use_sears_scattering_lengths = True
+            else:
+                print('Using scattering lengths from Neutron Data Booklet')
+                self._use_sears_scattering_lengths = False
+
         if magnetic_formfactor is not None:
             self._use_magnetic_form_factor = magnetic_formfactor
 
@@ -470,8 +484,11 @@ def structure_factor(self, hkl=None, scattering_type=None, int_hkl=True, **kwarg
                     qmag = fg.mag(_q)      # q magnitude
                     # Scattering factors
                     if scattering_type in fs.SCATTERING_TYPES['neutron']:
-                        # ff = fc.atom_properties(atom_type, 'Coh_b')
-                        ff = fc.neutron_scattering_length(atom_type)
+                        if self._use_sears_scattering_lengths:
+                            ff = fc.neutron_scattering_length(atom_type, 'Sears')
+                        else:
+                            # ff = fc.atom_properties(atom_type, 'Coh_b')
+                            ff = fc.neutron_scattering_length(atom_type)
                     elif scattering_type in fs.SCATTERING_TYPES['electron']:
                         ff = fc.electron_scattering_factor(atom_type, qmag)
                     elif scattering_type in fs.SCATTERING_TYPES['xray fast']:

Dans_Diffraction/data/README.md

@@ -23,6 +23,8 @@ $ ipython -i -m Dans_Diffraction
 ### Datasources
 The data is taken from a number of sources:
 * Neutron scattering lengths: [NIST](http://www.ncnr.nist.gov/resources/n-lengths/)
+* Neutron scattering lengths (Neutron Data Bookelet, 2003-2023)(default): [Periodic Table](https://github.com/pkienzle/periodictable)
+* Neutron scattering lengths (V. F. Sears 1995): [ITC](https://it.iucr.org/C/), Table 4.4.4.1
 * X-ray Form factor: [ITC](https://it.iucr.org/C/), p578, Table 6.1.1.4
 * X-ray Form factor (Waasmaier & Kirfel, Acta Cryst. A 51, 416-431 (1995)): [diffpy](https://github.com/diffpy/libdiffpy/blob/master/src/runtime/f0_WaasKirf.dat)
 * Magnetic Form Factor: [ILL](https://www.ill.eu/sites/ccsl/ffacts/ffactnode4.html)
@@ -86,7 +88,7 @@ Where f^0(|Q|) is the standard form factor and f', f'' are the dispersion correc
 online tables can be converted to f', f'' using the following:
  <div align="center">f' = f1 - f^0(0)</div>
  <div align="center">f'' = -f2</div>
-For a particular energy or energy range, f' and f'' can be calcualted, as well as the toal scattering factor:
+For a particular energy or energy range, f' and f'' can be calcualted, as well as the total scattering factor:
 
 ```python
 en = np.arange(5, 10, 0.001)
@@ -95,3 +97,20 @@ f1, f2 = dif.fc.xray_dispersion_corrections('Co', en)
 # Total: f0+f1+if2 (complex)
 f = dif.fc.xray_scattering_factor_resonant('Co', Qmag=0, energy_kev=en)
 ```
+
+### Neutron Scattering Lengths
+Neutron scattering lengths of elements and isotopes has been extracted from several sources:
+
+* [NIST Website](http://www.ncnr.nist.gov/resources/n-lengths/), with data originally from [V. F. Sears, Neutron News, Vol. 3, No. 3, 1992, pp. 29-37.](https://doi.org/10.1080/10448639208218770)
+* [Periodic Table](https://github.com/pkienzle/periodictable), with data originally from [Neutron Data Booklet](https://www.ill.eu/fileadmin/user_upload/ILL/1_About_ILL/Documentation/NeutronDataBooklet.pdf), by A-J Dianoux, G. Lander (2003), with additions and corrections upto v1.7.0 (2023) 
+* Table 4.4.4.1 in [International Tables Crystallography, Vol. C](https://it.iucr.org/C/) by V. F. Sears, 1995
+
+Thie NIST website values were originally used and stored in the `Dans Element Properties.txt` file with other elemental data.
+More recent values, including complex scattering lengths for isotopes are now included in `neutron_isotope_scattering_lengths.dat`.
+Complex isotope scattering lengths from the table by Sears(1995) is also included, stored in `neutron_isotope_scattering_lengths_sears.dat`.
+
+Neutron scattering lengths can be read using the built in functions:
+
+```python
+
+```