*.xtal File Description (version 1) Deprecated

•Contents of File

• <space_group_id>166:H</space_group_id>
  The Space Group id, This is the International Tabels number optionally followed by something to specify the setting"


• <space_group_IT_number>166:H</space_group_IT_number>
  The International Tabels number, an integer in range [1-20]"


• <H-M>166:H</H-M>  Optional
  H-M symbol, e.g. R -3 c:H


• <Hall>166:H</Hall>  Optional
  Hall symbol, e.g. -R 3 2''c


• <amcsd>0012345</amcsd>  Optional
  "American Minerologist Crystal Structue Database" database number


• <icsd>18189</icsd>  Optional
  "Inorganic Crystal Structue Database" database number


• <COD>9008678</COD>  Optional
  "Crystallography Open Database" database number


• <cell> ... </cell>
  This contains the information needed to define the unit cell, and optionally the measurment conditions.
  Required tags are the unit cell parameters:
  
  • <a>, <b>, <c>
    These are all of the form: <a unit="nm">0.4759092</a>
    where the unit is any length unit: nm, pm, Å, m, inch, parsec, and with prefixes, e.g. cm, or ypc, ...
    If the unit is not specified, it defaults to Å.
  • <alpha>, <beta>, <gamma>
    These are all of the form: <alpha unit="°">90</alpha>
    where the unit is one of [deg, °, rad, circle, arcmin, arcsec, grad, cos], again SI prefixes are allowed.
    If the unit is not specified, it defaults to degree.
  
  Optional tags are:
  • <temperature> Temperature where measurement was made.
    Again the temperature can have units, known units are: [C, K, F, R, Planck], default is K, and SI prefixes are allowed
  • <alphaT> Coefficient of expansion, used to get lattice constant at different temperatures. Units are 1/C.
• <atom_site> ... </atom_site>
  There should be one for each type of atom.
  Required tags are:
  
  • <label>
    These are all of the form: <label>Al01</label> or <label>Al</label>
    The value is a string that is unique for each atom site, numbers are usually used when the same element has multiple sites.
  
  
  • <fract_xyz>0 0 0.352</fract_xyz>
    The three number represent the fractional coordinates of the atom.
    
  
  Optionally the three {x,y,z}, can be specified separately as:
  • <fract_x>0</fract_x> The fractional X coordinate of the atom.
    
  • <fract_y>0</fract_y> The fractional Y coordinate of the atom.
    
  • <fract_z>0.352</fract_z> The fractional Z coordinate of the atom.
    
  
  Optional tags are:
  
  • <symbol>Al</symbol>
    Not needed if the element can be determined from the label.
    e.g. "Al01" → Al,  and "Ge" → Ge, but "atom1" → ???
  • <valence>3</valence>
    An integer describing the oxidation state. If not given, assume 0.
  • <occupancy>0.3</occupancy>
    The occupancy of the site, a number. If not given, assume 1. Should be in range (0,1].
  • <WyckoffSymbol>c</WyckoffSymbol>
    A letter that is the Wyckoff symbol. If not given, it will be determined from symmetry info.
    In this example it is "c"
  • <U_iso unit="Å^2">0.0049</U_iso>
    The isotropic U, in this example the units are Ų, any length² unit is allowed, default is Ų.
  • <B_iso unit="Å^2">1.1</B_iso>
    The isotropic B, in this example the units are Ų, any length² unit is allowed, default is Ų.
  • <aniso_U_11 unit="Å^2">0.01807</aniso_U_11>
    The anisotropic U values, in this example the units are Ų, any length² unit is allowed, default is Ų.
    You will probably also want to use: <aniso_U_22>, <aniso_U_33>, <aniso_U_12>, <aniso_U_13>, <aniso_U_23>
    Any unspecified values will be set to 0, and so have no effect.
  • <DebyeTemperature unit="K">670</DebyeTemperature>
    The Debye Temperature. This will allow a temperature dependent strength of reflections.
    The default unit is K, and all temperatuere units are allowed.
  
  
• <bond_chemical unit="nm" n0="Na1" n1="Cl001">0.2418</bond_chemical>   Optional
  Defines a bond. n0 and n1 refer to the label of two atom types (can be the same), and the value is the bond length.


• <citation> ... </citation>
  Holds the citation of the article where these values came from.
  The opener can specify a "doi" as in: <citation doi="10.1107/S0365110X63002012">
  The contents of the <citation> block is just plain text (see version 2 for strcuture).

•Exmaple File, (Not Real Values)

<?xml version="1.0" encoding="UTF-8" ?>

<cif>    // everything about the structure is in <cif> ... </cif>
  <chemical_name_common>NaCl, table salt</chemical_name_common> // This is the name you want to call this structure
  <chemical_formula_structural>Ca5 (P04)3 (OH)</chemical_formula_structural>   // OPTIONAL
  <space_group_id>166:H</space_group_id>    // space group id, there are 530 of these. USE this, and NOT <space_group_IT_number>
  <space_group_IT_number>225</space_group_IT_number>   // space group number from International Tables [1-230]
  <H-M>Fm-3m</H-M>    // OPTIONAL, symmetry symbol
  <Hall>-F 4 2 3</Hall>    // OPTIONAL, Hall symbol
  <amcsd>0012345</amcsd>    // OPTIONAL, AMCSD number
  <icsd>18189</icsd>    // OPTIONAL, ICSD number
  <cell>    // the <cell> ... </cell> describes the unit cell
    <a unit="pm">564.02</a>    // for a, b, c, allowed units are Angstrom, m, inch, mile, yard, parsec, lightYear
    <b unit="pm">564.02</b>    // along with a prefix, e.g. "nm", or "pparsec"
    <c unit="pm">564.02</c>    // default units are Angstroms, this example shows pico-meters.
    <alpha>90</alpha>      // angles (degree)
    <beta>90</beta>
    <gamma>90</gamma>
    <temperature unit="C">20</temperature>    // OPTIONAL, temperature if known, and alphaT is the thermal expansion coefficient
    <alphaT>5.9e-06</alphaT> <!-- a = ao*(1+alphaT*(TempC-20)) -->   // OPTIONAL, also formula for calculating a(T)
  </cell>

  <atom_site>    // There is one <atom_site>...</atom_site> tag for each symmetry inequivalent atom
    <label>Na1</label>    // This is just a string to id the atom type, the labels should all be different
    <symbol>Na</symbol>    // the atomic symbol, first letter is uppercase, second is lower
    <fract_xyz>0 0 0</fract_xyz>    // position of this atom in fractional coordinates
    <occupancy>0.95</occupancy>    // OPTIONAL, occupancy, must be in range (0,1], default is 1
    <WyckoffSymbol>a</WyckoffSymbol>    // OPTIONAL , see http://www.cryst.ehu.es/ for Wyckoff symbols
    <DebyeTemperature unit="K">670</DebyeTemperature>   // OPTIONAL, Debye Temperature, units are C or F, default is infinite
    <!-- The Debye Temperatuers are made up -->   // an example of a comment
    <aniso_U_11 unit="Å^2">123</aniso_U_11>    // OPTIONAL, all of the U_ij and U_iso are optional
    <aniso_U_22 unit="Å^2">162</aniso_U_22>
    <aniso_U_33 unit="Å^2">1</aniso_U_33>
  </atom_site>

  <atom_site>
    <label>K1</label>    // so this is 95%NaCl + 5%KCl
    <symbol>K</symbol>
    <fract_x>0</fract_x>    // this old style still works, this looks more like cif
    <fract_y>0</fract_y>
    <fract_z>0</fract_z>
    <occupancy>0.05</occupancy>
    <DebyeTemperature unit="K">670</DebyeTemperature>
    <WyckoffSymbol>a</WyckoffSymbol>
    <U_iso unit="Å^2">123</U_iso>    // or perhaps <B_iso>9</B_iso>
  </atom_site>

  <atom_site>
    <label>Cl001</label>
    <symbol>Cl</symbol>
    <fract_xyz>0.5 0.5 0.5</fract_xyz>
    <WyckoffSymbol>b</WyckoffSymbol>
    <DebyeTemperature unit="K">670</DebyeTemperature>
  </atom_site>

  <bond_chemical unit="nm" n0="Na1" n1="Cl001">0.2418</bond_chemical>   // OPTIONAL, n0 & n1 refer to labels of defined atoms, and the value is the bond length.
  <bond_chemical unit="nm" n0="K1" n1="Cl001">0.2399</bond_chemical>   // one line for each TYPE of bond.

  <citation doi="10.1103/328606a0">Smith, Jones, Gupta, Acta Cryst. 78, (2008) 020503(R)</citation>   // OPTIONAL, where this information came from
</cif>