(sw-mff)=

# sw_mff

## Syntax
  
`[~, coeff, s] = sw_mff(atomname)`
  
`[formfactval, coeff, s] = sw_mff(atomname,Q)`
 
## Description
  
`[~, coeff, s] = sw_mff(atomname)` returns the magnetic form
factor coefficients for the magnetic atom identified by a string, e.g.
`'MCR3'`. The function reads the `magion.dat` file for the stored form
factor coefficients.
 
`[formfactval, coeff, s] = sw_mff(atomname,Q)` also calculates the form
factor values at the given $Q$ points (in Å$^{-1}$ units.
 
The source of the form factor data are:
1. A.-J. Dianoux and G. Lander, Neutron Data Booklet (2003).
2. K. Kobayashi, T. Nagao, and M. Ito, Acta Crystallogr. A. 67, 473 (2011).
 
## Input Arguments
  
`atomName`
: String, contains the name of the magnetic ion in FullProf
  notation (e.g. for Cr$^{3+}$ use `'MCR3'` or `'Cr3'`). It can be also a
  vector of the 7 form factor coefficients. If the string contains
  whitespace, the first word will be used as input. Can be also a cell of
  strings to calculate coefficients for multiple ions.
  
`Q`
: Momentum transfer in Å$^{-1}$ units in a matrix with dimensions of
  $[1\times n_Q]$ or $[3\times n_Q]$.
  
## Output Arguments
  
`formFactVal`
: Value of the form factor, evaluated at the given $Q$ points.
 
`coeff`
: Form factor coefficients according to the following formula:
    
  $$\langle j_0(Q_s)\rangle = A\exp(-a\cdot Q_s^2) + B\exp(-b\cdot Q_s^2) + C\exp(-c\cdot Q_s^2) + D\exp(-d\cdot Q_s^2) + E$$
 
  where $Q_s = \frac{Q}{4\pi}$ and $A$, $a$, $B$, ... are the coefficients.
  The $D$ and $d$ coefficients can be zero.
  
`S`
: Value of the spin quantum number (read from the spin column in `magion.dat`).