(sw-cff)=

# sw_cff

## Syntax
  
`[formfactval, coeff] = sw_cff(atomname, {q})`
  
## Description
  
`[formfactval, coeff] = sw_cff(atomname, {q})` returns the atomic charge
form factors for x-ray scattering. The provided form factor values at Q=0
are normalized to Z.
  
## Input Arguments
  
`atomName`
: String, contains the name of the ion in using the symbol of
  the element following the charge, e.g. `'Cr3+'`. It can be also
  the coefficients to calculate f. If the string contains
  whitespace, the first word will be used as input.
  
`Q`
: Momentum transfer in Å$^{-1}$ units in a matrix with dimensions of
  $[1\times n_Q]$ or $[3\times n_Q]$, optional.
  
## Output Arguments
  
`formFactVal`
: Value of form factor, evaluated at the $Q$ points if $Q$ is
              defined.
 
`coeff`
: Form factor coefficients according to the following
              formula:
                  $f_0(Q_s) = c + \sum_{i=1}^5 a_i\cdot \exp(-b_i Q_s^2)$,
              where $Q_s = \frac{Q}{4*\pi}$ and $[a_1, b_1, a_2, b_2, ... c]$ are the
              coefficients.
  
## See Also
  
[sw_mff](#sw-mff)