Fractional coordinates and scattering parameters for a given chemical element

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Description

Get fractional coordinates, neutron scattering length and X-ray scattering factor.

Usage

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Arguments

name

name of chemical element; see details.

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scatterFactor

list containing scattering factor parameters as returned by getScatterFactor.

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Q

numeric vector containing grid points at which scattering factor should be calculated.

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Details

getScatterLength contains data for neutron scattering lengths of the elements and their isotopes taken from http://www.ncnr.nist.gov/resources/n-lengths/list.html. Parameter name should be given as in the corresponding table.

getScatterFactor contains data for X-ray scattering factors of the elements and their isotopes taken from Waasmaier et al., 1995. Parameter name should be given as in table 1. The atomic scattering factor is calculated using the method developed by Waasmaier et al. that implies approximation by a function

f(s)=a_1 * exp(-b_1 s) + a_2 * exp(-b_2 s) + a_3 * exp(-b_3 s) + a_4 * exp(-b_4 s) + c

, with s = (\frac{Q}{4π})^2.

getBase() function contains information about fractional coordinates for certain simple structure. Parameter name can be:

"Cu" to specify fractional coordinates of atoms in monoatomic fcc lattice,

"Fe" to specify fractional coordinates of atoms in monoatomic bcc lattice,

"Na" to specify fractional coordinates of Na atoms in NaCl rock salt structure,

"Cl" to specify fractional coordinates of Cl atoms in NaCl rock salt structure,

"Ca" to specify fractional coordinates of Ca atoms in CaTiO3 ideal perovskite structure,

"Ti" to specify fractional coordinates of Ti atoms in CaTiO3 ideal perovskite structure,

"O3" to specify fractional coordinates of O atoms in CaTiO3 ideal perovskite structure,

"Mg" to specify fractional coordinates of atoms in monoatomic hcp lattice,

"Zn" to specify fractional coordinates of Zn atoms in ZnS wurtzite structure,

"S" to specify fractional coordinates of S atoms in ZnS wurtzite structure.

Value

getBase: numeric matrix in which each row represents fractional coordinates of the corresponding atom within the primitive cell.

getScatterLength: numeric describing neutron scattering length for the given element.

getScatterFactor: list containing X-ray scattering factor parameters for the given element.

scatterFactor: numeric vector containing scattering factor value(s).

References

Waasmaier D. and Kirfel A. (1995): New analytical scattering-factor functions for free atoms and ions. Acta Cryst. A51, 416–431.

See Also

createAtom

Examples

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## get fractional coordinates for Zn
Cd_base <- getBase("Zn")  
## get scattering parameters for Cd
Cd_scL <- getScatterLength("Cd") 
Cd_scF <- getScatterFactor("Cd")

Se_base <- getBase("S")
Se_scL <- getScatterLength("Se")
Se_scF <- getScatterFactor("Se")

Q <- seq(0.1, 15, 0.1)
## plot scattering factor
plot(Q, scatterFactor(Se_scF, Q))