praxes.physref.waasmaier

The waasmaier module provides an interface to the energy-independent atomic form factors, as calculated by D. Waasmaier and A. Kirfel in Acta. Cryst. vA51, p416 (1995). The calculations take the form

f_0(s) = \sum_{i=0}^{5} a_i e^{-b_i s^2} + c

This approximation is valid for s ≤ 6 \AA^{-1}, or |Q| ≤ 75 \AA^{-1}.

Atomic form factors accessed using atomic_data:

>>> from praxes.physref.waasmaier import atomic_data
>>> import quantities as pq
>>> f0 = atomic_data['O']
>>> print f0(0 * 1/pq.angstrom)
7.99706
>>> print f0([0,1,2] * 1/pq.angstrom)
array([ 7.999706  ,  7.50602869,  6.31826029])
>>> f0 = atomic_data['O2-']
>>> print f0(0* 1/pq.angstrom)
9.998401

Module Interface

class praxes.physref.waasmaier.atomicdata.AtomicData
get(item, default=None)

Return the value for key, or return default

items()

Return a new view of the (key, value) pairs

iteritems() → an iterator over the (key, value) items of D
iterkeys() → an iterator over the keys of D
itervalues() → an iterator over the values of D
keys()

return a new view of the keys

values()

return a new view of the values

class praxes.physref.waasmaier.atomicdata.FormFactor(symbol, db)

FormFactor instances are callable to calculate the energy-independent form factors. They should be called with a Quantity in units of 1/length.