Experimental verification of Debye-Waller factor calculation

[mducle]

The Debye-Waller factor calculation is the only part of Euphonic which was not verified / confronted with experimental data when the paper was written.

Recently @davidvoneshen found that the calculated D-W factor dropped off much more sharply with Q than his data, however this was on a very complex system and it would be better to verify the calculation using a simple monatomic system (such as Silicon, Al or Cu).

This will require a measurement on either MERLIN or MARI at 5K and 300K.