1
Structural Biology
Methods
Fall 2020
Lecture #3
System of two electrons
Scattering by a unit cell
Scattering by a crystal
Reciprocal lattice and Ewald construction
https://youtu.be/qCQmT_N6_fA
Temperature (B) factor
Calculation of electron density
The structure factor is a function of the electron
density distribution in the unit cell:
Scattering by a unit cell
Calculation of electron density
The structure factor is a function of the electron
density distribution in the unit cell:
Information from X-ray diffraction
experiment
[0;0;0] x
y
z
Notes
Intensity diffracted by a crystal
λ – wavelength
ω – angular velocity of crystal
rotation
V – unit cell volume
e – electron charge
m – electron mass
c – speed of light
Vcr – crystal volume
I0 – intensity of the excitation beam
L – Lorentz coefficient
P – polarization coefficient
Tr – transmission coefficient
|F(hkl)| - structure factor amplitude
Effect of the unit cell size on the diffraction
intensity
Friedel pairs
Symmetry in the diffraction pattern
For F(hkl) with k odd:
Systematic absences in P2(1)