Basic examples
Single atom
Pair of atoms
Row of atoms
Interactive examples
1D crystal builder
Polygons of atoms
Different atoms
Ewald sphere
Units
Interference
Bragg's law
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Example direct space:
 As you increase the unit length, the coordinates of the
atoms decrease and vice versa.
 Given the unit lengths of 5 and 8 Ångstroems,
respectively, the coordinates of all atoms are exact
integer numbers. The periodicity of this crystal is
5 Ångstroem along the x and 8 Ångstroem along the
y axis. One would refer to these values as the unit cell
constants of the material.
Example reciprocal space:
 As you increase the unit length, the coordinates of the
Bragg reflections decrease and vice versa. The measurement
in reciprocal space, however, is in 1/Ångstroem !
 The values of 0.2 and 0.125 A^{1} along the x and y axis,
respectively, yield integer coordinates for all Bragg reflections.
Incidentally, these values are the reciprocal values to the
lattice constants of the Example A. This simple relationship,
however, is only valid in rectangular lattices, as you will
see later on.
 The unit lengths of h are 0.2 and 0.125
Å^{1}
 The unit lengths of Q is 6.28
Å^{1}.
In crystallography, the Fourier transform is written as
e^{(2π i hr) }and reciprocal space is
measured in multiples of the reciprocal lattice constants.
Physicists, often use the formula e^{(i Qr)}
and measure reciprocal space in units of Q=2π h,
resulting in the scale factor of 2π=6.28. When you
describe periodic structures and their reciprocal space,
the unit h is definetely better suited. For
nonperiodic structures like glasses the difference is
more a matter of taste and willingness to carry around
an extra 2π..
