Electronic disorder

Ferrari AC (2007) Raman spectroscopy of graphene and graphite disorder, electron-phonon coupling, doping and nonadiabatic effects. Solid State Commun 143(l-2) 47-57... 

When the determination of a crystal structure is difficult or refinement gives a strangely shaped molecule, it is possible that the molecule is disordered in a site in the crystal. This happens when the available space in the crystal is such as to accommodate two different orientations of the molecule. For example, in the crystal structure of 5-methylchrysene, -one of the two molecules in the asymmetric unit is disordered. It was difficult to solve the crystal structure until the nature of the disorder was realized. In a given site, this disordered molecule may be in one of two possible orientations. In some places in the disordered electron density map, atoms in the two orientations of the disordered molecule are near each other and their positions can be approximated (erroneously) by the use of highly anisotropic temperature parameters. The result is that the anisotropic temperature parameters on refinement do not make any sense until the nature of the disorder is understood. 

The decreased kinetic energy of the electrons in the metallic bonds reduces the possibility of disordered electron movements, facilitating the transport of electrical charges and heat. It is these features of electrical and thermal conductivity that make the crystalline metallic bond differ from the ionic bond in crystals (e.g., structure of NaCl). 

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