.. _xraydb-chapter:

=====================
X-ray Databases
=====================

.. module:: _xray
   :synopsis: X-ray Properties

An important aspect of X-ray spectroscopies and scattering analysis is
having access to tabulated values for X-ray properties of various elements
and compounds.  Larch provides several functions to access these X-ray
properties, which can be broken into two general categories:  X-ray
properties of elements, and properties of materials and compounds by
chemical formula.

The first category includes basic atomic properties like atomic number and
mass, and consists of tabulated values of characteristic energies and
transition probabilites for core electron levels, absorption
cross-sections, elastic scattering terms, and anomalous scattering factors.
The second category allows these elemental properties to be applied to
common compounds by name or by chemical formula.

Much of the X-ray spectroscopic data comes from the compilation of Elam *et
al* :cite:`Elam_etal`.  The core-hole widths for excited electronic levels
comes from Keski-Rahkonen and Krause :cite:`Keski_Krause` and Krause and
Oliver :cite:`Krause_Oliver`, while elastic X-ray scattering data,
:math:`f_0(q)`,is derived from Waasmaier and Kirfel
:cite:`Waasmaier_Kirfel`.  Anomalous cross-sections are available as based
on the work of Cromer and Liberman :cite:`Cromer_Liberman`, using the
implementation of Brennan and Cowan :cite:`Brennan_Cowan`.  In addition,
values for absorption cross-sections and anomalous X-ray scattering factors
from Chantler :cite:`Chantler` (as from
http://www.nist.gov/pml/data/ffast/index.cfm) are available.  Except for
the anomalous cross-section data from Cromer and Liberman (which is
implemented using the Fortran routine by Brennan and Cowan with slight
modifications), the data is accessed through a portable SQLite3 database
file.  This implementation was originally done by Darren Dale from CHESS
(see https://github.com/praxes/elam_physical_reference), with some
additions and alterations made for Larch.

X-ray Properties of the Elements
---------------------------------

The :ref:`Table of X-ray data functions <xraydb-elem_funcs_table>` gives a brief
description to the available functions for accessing these data.  More
detailed descriptions of function arguments, returned values, and so on are
then given.

.. index:: X-ray data resources for the elements
.. _xraydb-elem_funcs_table:

    Table of X-ray database functions for the Elements.  These functions
    calculate and return some element-specific properties, given the
    element symbol or atomic number.  Most data extends to Z=98 (Cf).  Data
    for elements with atomic number > 92 (U) may not be available and when
    provided may not be very reliable.  Except where noted, the data comes
    from Elam, Ravel, and Sieber.

     ========================== =============================================================
      function                    description
     ========================== =============================================================
      :func:`atomic_number`      atomic number from symbol
      :func:`atomic_symbol`      atomic symbol from number
      :func:`atomic_mass`        atomic mass
      :func:`atomic_density`     atomic density (for pure element)
      :func:`xray_edge`          xray edge data for a particular element and edge
      :func:`xray_line`          xray emission line data for an element and line
      :func:`xray_edges`         dictionary of all X-ray edges data for an element
      :func:`xray_lines`         dictionary of all X-ray emission line data for an element
      :func:`fluo_yield`         fluorescence yield and weighted line energy
      :func:`core_width`         core level width for an element and edge (Keski-Rahkonen and Krause, Krause and Oliver)
      :func:`mu_elam`            absorption cross-section
      :func:`coherent_xsec`      coherent cross-section
      :func:`incoherent_xsec`    incoherent cross-section
      :func:`f0`                 elastic scattering factor (Waasmaier and Kirfel)
      :func:`f0_ions`            list of valid "ions" for :func:`f0` (Waasmaier and Kirfel)
      :func:`chantler_energies`  energies of tabulation for Chantler data (Chantler)
      :func:`f1_chantler`        f'  anomalous factor (Chantler)
      :func:`f2_chantler`        f'' anomalous factor (Chantler)
      :func:`mu_chantler`        absorption cross-section (Chantler)
      :func:`xray_delta_beta`    anomalous components of the index of refraction for a material
      :func:`f1f2_cl`            f' and f'' anomalous factors (Cromer and Liberman)
     ========================== =============================================================

A few conventions used in these functions is worth mentioning.  Almost all these functions require
an element to be specified for the first argment, noted as ``z_or_symbol`` in the functions below.
This can either be a valid atomic number or a case-insensitive atomic symbol.  Thus, ``28``, ``Co``
and ``co`` all specify cobalt.  Several functions take either an ``edge`` or a ``level`` argument
to signify an core electronic level.  These must be one of the levels listed in the :ref:`Table of
X-ray edge names <xraydb-edge_table>`.  Some functions take emission line arguments.  These follow
the latinized version of the Siegbahn notation as indicated in the :ref:`Table of X-ray emission
line names <xraydb-lines_table>`.  Finally, all energies are in eV.

.. index:: Table of X-ray edge names
.. _xraydb-edge_table:

    Table of X-ray Edge / Core electronic levels

   +-----+-----------------+-----+-----------------+-----+-----------------+
   |Name |electronic level |Name |electronic level |Name |electronic level |
   +=====+=================+=====+=================+=====+=================+
   | K   |    1s           | N7  |    4f7/2        | O3  |     5p3/2       |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | L3  |    2p3/2        | N6  |    4f5/2        | O2  |     5p1/2       |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | L2  |    2p1/2        | N5  |    4d5/2        | O1  |     5s          |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | L1  |    2s           | N4  |    4d3/2        | P3  |     6p3/2       |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | M5  |    3d5/2        | N3  |    4p3/2        | P2  |     6p1/2       |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | M4  |    3d3/2        | N2  |    4p1/2        | P1  |     6s          |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | M3  |    3p3/2        | N1  |    4s           |     |                 |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | M2  |    3p1/2        |     |                 |     |                 |
   +-----+-----------------+-----+-----------------+-----+-----------------+
   | M1  |    3s           |     |                 |     |                 |
   +-----+-----------------+-----+-----------------+-----+-----------------+

.. index:: Table of X-ray emission lines
.. _xraydb-lines_table:

    Table of X-ray emission line names and the corresponding Siegbahn and IUPAC notations

   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Name   | Siegbahn                    | IUPAC     | Name   | Siegbahn                    | IUPAC       |
   +========+=============================+===========+========+=============================+=============+
   | Ka1    | :math:`K\alpha_1`           | K-L3      | Lb4    | :math:`L\beta_4`            | L1-M2       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Ka2    | :math:`K\alpha_2`           | K-L2      | Lb5    | :math:`L\beta_5`            | L3-O4,5     |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Ka3    | :math:`K\alpha_3`           | K-L1      | Lb6    | :math:`L\beta_6`            | L3-N1       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Kb1    | :math:`K\beta_1`            | K-M3      | Lg1    | :math:`L\gamma_1`           | L2-N4       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Kb2    | :math:`K\beta_2`            | K-N2,3    | Lg2    | :math:`L\gamma_2`           | L1-N2       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Kb3    | :math:`K\beta_3`            | K-M2      | Lg3    | :math:`L\gamma_3`           | L1-N3       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Kb4    | :math:`K\beta_2`            | K-N4,5    | Lg6    | :math:`L\gamma_6`           | L2-O4       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Kb5    | :math:`K\beta_3`            | K-M4,5    | Ll     | :math:`Ll`                  | L3-M1       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | La1    | :math:`L\alpha_1`           | L3-M5     | Ln     | :math:`L\nu`                | L2-M1       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | La2    | :math:`L\alpha_1`           | L3-M4     | Ma     | :math:`M\alpha`             | M5-N6,7     |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Lb1    | :math:`L\beta_1`            | L2-M4     | Mb     | :math:`M\beta`              | M4-N6       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Lb2,15 |:math:`L\beta_2,L\beta_{15}` | L3-N4,5   | Mg     | :math:`M\gamma`             | M3-N5       |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+
   | Lb3    | :math:`L\beta_3`            | L1-M3     | Mz     | :math:`M\zeta`              | M4,5-N6,7   |
   +--------+-----------------------------+-----------+--------+-----------------------------+-------------+



.. function:: atomic_number(symbol)

    return the atomic number from an atomic symbol ('H', 'C', 'Fe', etc)

.. function:: atomic_symbol(z)

    return the atomic symbol from an atomic number

.. function:: atomic_mass(z_or_symbol)

    return the atomic mass in amu from an atomic number or symbol

.. function:: atomic_density(z_or_symbol)

   return the density of the common form of a pure element, in gr/cm^3, from an atomic number or symbol.


.. function:: xray_edge(z_or_symbol, edge_name)

    return (edge energy, fluorescence yield, edge jump) for an atomic number or symbol and
    name of the edge.  Edge energies are in eV.

.. function:: xray_line(z_or_symbol, line_name)

    return (emission energy, intensity, initial level, final level)for an atomic number or symbol
    and name of the emission line.  The intensity is the probability of emission from the given
    initial level.

.. function:: xray_edges(z_or_symbol)

    return dictionary of all (edge energy, fluorescence yield, edge jump) for an atomic number or
    symbol.  The keys of the dictionay are the names of the edges.

.. function:: xray_lines(z_or_symbol)

    return dictionary of all (emission energy, intensity, initial level, final level for an atomic
    number or symbol.  The keys of the dictionay are the names of the emission lines.

.. function:: fluo_yield(z_or_symbol, edge, emission_family, incident_energy, energy_margin=-150)

    return (fluorescent yield, average emission energy, probability)
    for an atomic number or symbol, edge, emission family, and incident
    energy.

    Here, 'emission family' is the family of emission lines, 'Ka', 'Lb',
    etc, that is comprised of several individual lines ('Ka1', 'Ka2',
    'Lb2', etc).  The returned average emission energy will be the average
    of the corresponding individual sub-line energies, weighted by the
    probabilities of the individual lines.  The returned probability will
    be the total probability for all lines in the family.

    The fluorescence yield will also be returned, giving the same value as
    :func:`xray_edge` if the provided incident_energy is above or near the
    corresponding edge energy.  The energy_margin controls the allowed
    proximity to the edge energy, so that the returned fluorescence yield
    will be 0 if the incident energy < edge energy + energy_margin.


.. function:: core_width(z_or_symbol, edge)

    return core electronic level width for an atomic number or symbol and
    name of the edge.  widths are in eV.

.. function:: mu_elam(z_or_symbol, energy, kind='total')

    return X-ray mass attenuation coefficient :math:`\mu/\rho` in cm^2/gr
    for an atomic number or symbol at specified energy values.

    :param z_or_symbol:  Integer atomic number or symbol for elemen
    :param energy:       energy (single value, list, array) in eV at which
                         to calculate :math:`\mu`.
    :param kind:         one of 'total' (default), 'photo', 'coh', and 'incoh' for
                         total, photo-absorption, coherent scattering, and
                         incoherent scattering cross sections, respectively.


.. function:: coherent_xsec(z_or_symbol, energies)

    return coherent scattering cross-section for an atomic number or symbol at
    specified energy values.  Values returned are in cm^2/gr.

.. function:: incoherent_xsec(z_or_symbol, energies)

    return incoherent scattering cross-section for an atomic number or symbol at
    specified energy values. Values returned are in cm^2/gr.


.. function:: f0(ion, qvalues)

   return elastic scattering (Thomson) factor :math:`f_0(q)` for the supplied values of
   ``q`` (:math:`q = \sin(\theta)/\lambda` where :math:`\theta` is the scattering angle
   and :math:`\lambda` is the X-ray wavelength).  Here, ``ion`` can be an atomic number or
   symbol, or any of the valid ion values (e.g., 'Ga3+') given by Waasmaier and Kirfel.
   The returned values are in units of electron number.

.. function:: f0_ions(element=None)

    returns list of valid ions for :func:`f0`.  If ``element`` is given (either an atomic number or
    symbol), then only the valid ions for that element will be returned.

.. index:: anomalous X-ray scattering factors

.. function:: chantler_energies(z_or_symbol, emin=0, emax=1.e9)

   returns array of energies (in eV) at whch data is tabulated in the Chantler tables.
   The arguments ``emin`` and ``emax`` can be used to restrict the range of returned energies.

.. function:: f1_chantler(z_or_symbol, energies)

   return array of f', the real part of the anomalous scattering factor for an element at
   the given energies, using the tabulation of Chantler.  The returned values are in units
   of electron numbers, and represent the correction to Thomson scattering term.

.. function:: f2_chantler(z_or_symbol, energies)

   return array of f'', the imaginary part of the anomalous scattering factor for an
   element at the given energies, using the tabulation of Chantler.  The returned values
   are in units of electron numbers.  These values scale to the values of the mass
   attenuation coefficient.

.. function:: mu_chantler(z_or_element, energies)

    return X-ray mass attenuation coefficient (:math:`\mu/\rho`) for an element at the
    specified energy values, using the tabulation of Chantler.

.. function:: f1f2_cl(z_or_element, energies, width=None, edge=None)

    return tuple of (f', f''), the real and imaginary anomalous scattering factors for an
    element at the specified energies, using the calculation scheme of Cromer and
    Liberman, as implemented by Brennan and Cowan.  The optional argument ``width`` can be
    used to specify an energy width (in eV) to use to convolve the output with a
    Lorentzian profile (with ``width`` used as :math:`2\gamma` in the Lorentzian).  If
    ``edge`` is given ('K', 'L3', etc), the core-level width is looked up from
    :func:`core_width`, and its value is used.

    Note that both f' and f'' are returned here.

.. warning::

   The Cromer-Liberman calculation sometimes generate spurious data,
   especially at high and low energies.  The data from Chantler's tables
   should be used in its place.  That is, in almost all places where the
   Cromer-Liberman values differ from the Chantler values, the
   Cromer-Liberman data is obviously wrong.

   The Cromer-Liberman tables are kept for historical reasons and backward
   compatibility, but may be dropped in the future.


X-ray Properties of Materials and Chemicals
---------------------------------------------

Compositional data for several common materials are included with Larch,
and can be read at run time.  The variable ``_xray.materials`` contains a
dictionary of material names, with values of (chemical forumla, density)
that are read on startup, and can be appended too.  There is a system-wide
set of 50 or so known materials, and you can add your own favorite
materials that will then be automatically available in later sessions.


The :ref:`Table of X-ray functions for materials <xraydb-materials_funcs_table>`
gives a brief description to the available functions for accessing these
data.  More detailed descriptions of function arguments, returned values,
and so on are then given.

.. index:: X-ray data resources for materials
.. _xraydb-materials_funcs_table:

    Table of X-ray database functions for materials.  These functions
    calculate and return X-ray properties for known materials or chemical
    formula. Except where noted, the data comes from Elam, Ravel, and
    Sieber.

     =============================== =============================================================
      function                          description
     =============================== =============================================================
      :func:`chemparse`               parse a chemical formula to a dictionary of components
      :func:`material_get`            get dictionary of elements for a known material
      :func:`material_add`            add a material to list of known materials
      :func:`material_mu`             calculate :math:`\mu` for a material or chemical formula
      :func:`material_mu_components`  calculate components of :math:`\mu` for a material or
                                      chemical formula
      :func:`xray_delta_beta`         anomalous index of refraction for a
                                      material, using data from Chantler.
     =============================== =============================================================


.. function:: chemparse(formula)

   parse a chemical formula, returning a dictionary with element symbols as
   keys and number for each element as values.  For example::

        larch> chemparse("H2O")
        {'H': 2.0, 'O': 1}
        larch> chemparse("Mg0.2Fe0.8(SO4)2")
        {'S': 2.0, 'Mg': 0.2, 'Fe': 0.8, 'O': 8.0}

   Note that factional weights and scientific notation for weights is
   supported, as long as the weight begins with a number and not '.'.  That
   is 'Fe0.8' is supported, but 'Fe.8' is not.


.. function:: material_get(name)

   look up chemical compound by naming returning formula (not parsed!) and
   density.  For example::

        larch> material_get('kapton')
        ('C22H10N2O5', 1.43)

   material names are not case sensitive.

.. function:: material_add(name, formula, density)

   add material with name, chemical formula, and density.  This will be
   added to the a file in the user's larch directory, and loaded in
   subsequent larch sessions.

   material names are not case sensitive.

.. function:: material_mu(name_or_formula, energy, density=None)

   return X-ray attenuation length (in 1/cm) for a material, either by name
   or formula and density.


    return X-ray mass attenuation coefficient :math:`\mu/\rho` in cm^2/gr
    for an atomic number or symbol at specified energy values.

    :param name:    material name or formula
    :param energy:  energy (single value, list, array) in eV at which
                    to calculate :math:`\mu`.
    :param kind:    one of 'total' (default), 'photo', 'coh', and
                    'incoh' (see :func:`mu_elam`)
    :param density: material density (if ``None``, it will be looked up for
                    known materials)
    :return:        :math:`\mu` in 1/cm.

    uses :func:`mu_elam`. Example::

      larch> print material_mu('water', 10000.0)
      5.32986401658495
      larch> print material_mu('H2O', 10000.0, density=1.0)
      5.32986401658495

.. function:: material_mu_components(name_or_formula, energy, density=None)

    return dictionary of components to calculate absorption coefficient.

    :param name:    material name or formula
    :param energy:  energy (single value, list, array) in eV at which
                    to calculate :math:`\mu`.
    :param kind:    one of 'total' (default), 'photo', 'coh', and
                    'incoh' (see :func:`mu_elam`)
    :param density: material density (if ``None``, it will be looked up
                    for known materials)
    :return:        dictionary of data for constructing :math:`\mu` per element.

    The returned dictionary will have elements 'mass' (total mass), 'density', and
    'elements' (list of atomic symbols for elements in material). For each element, there
    will be an item (atomic symbol as key) with tuple of (fraction, atomic mass, :math:`\mu`).
    For example::

       larch> material_mu_components('quartz', 10000)
       {'Si': (1, 28.0855, 33.879432430185062), 'elements': ['Si', 'O'],
       'mass': 60.0843, 'O': (2.0, 15.9994, 5.9528248152970837), 'density': 2.65}

.. function:: xray_delta_beta(material, energy, photo_only=False)

    return anomalous components of the index of refraction for a material,
    using the tabulated scattering components from Chantler.

    :param material:   chemical formula  ('Fe2O3', 'CaMg(CO3)2', 'La1.9Sr0.1CuO4')
    :param density:    material density in g/cm^3
    :param energy:     X-ray energy in eV
    :param photo_only: boolean for returning only the photo cross-section component
                       for beta and t_atten. If ``False`` (the default value), the
                       total cross-section is returned.
    :return:           (delta, beta, t_atten)

    The material formula is parsed by :func:`chemparse`.   The returned
    tuple contains the components described in the table below

      ============== ================= ===============================================
         value         symbol            description
      ============== ================= ===============================================
         delta        :math:`\delta`     real part of index of refraction.
         beta         :math:`\beta`      imaginary part of index of refraction.
         t_atten      :math:`t_a`        attenuation length, in cm.
      ============== ================= ===============================================

    and correspond to the anomalous scattering components of the index of
    refraction, defined in the equation below.  Here, :math:`t_{a} =
    \lambda / 4\pi\beta`, and and :math:`\lambda` is the X-ray wavelength,
    :math:`r_0` is the classical electron radius, and the sum is over the
    atomic species with number :math:`n_j` and total complex scattering
    factor :math:`f_j`.

.. math::
    n = 1 - \delta - i \beta = 1 - \lambda^2 \frac{r_{0}}{2\pi} \sum_j{ n_j  f_j}


.. rubric:: References

.. bibliography:: ../larch.bib
   :style: unsrt
   :labelprefix: Xray_
   :filter: docname in docnames
