Wednesday, March 25, 2015

Enhanced teaching of crystal structures

This past week I taught my condensed matter class about crystal structures and their determination by X-rays. This can be a little dry and old. Here, are few things I do to try and make things more interesting and relevant. I emphasise that many of these developments go beyond what was known or anticipated when Ashcroft and Mermin was written. Furthermore, significant challenges remain.

Discuss whether the first X-ray crystallography experiment the most important experiment in condensed matter, ever?

Take crystal structure "ball and stick" models to the lectures.

Give a whole lecture on quasi-crystals.

Use the bravais program in Solid State Simulations to illustrate basic ideas. For example, the equivalence of each reciprocal lattice vector to an X-ray diffraction peak, to a family of lattice planes in real space, and to a Miller indice.

Show a crystal structure for a high-Tc cuprate superconductor and an organic charge transfer salt. Emphasize the large number of atoms per unit cell and how small changes in distances can totally change the ground state (e.g. superconductor to Mott insulator). Furthermore, these small changes may be currently beyond experimental resolution. This is very relevant to my research and that of Ben Powell.

Very briefly mention the Protein Data Bank, and its exponential growth over the past few decades. It now contains more than 100,000 bio-molecular structures. Mention the key concept that Structure determines Property determines Function. Mention that although many structures resolve bond lengths to within 0.2-0.6 Angstroms, that this just isn't good enough to resolve some important questions about chemical mechanisms related to function. I am currently writing a paper on an alternative "ruler" using isotopic fractionation. 

Next year I may something about the importance of synchrotrons and neutron sources, and crystallographic databases such as the Cambridge Structural Database, which contains more than 700,000 structures for small organic molecules and organometallics.


  1. Hi Ross,

    maybe you could expand on the discussion regarding X-ray crystallography being the most important experiment in condensed matter ever. I've being reading the book "Out of the Crystal Maze", which gives an interesting account on the history of solid state physics until the 1960s and although X-rays really impress me I tend to have liquid helium in a higher status, due to it opening the "low temperatures door to new phenomena".

    In either case I remember that during my graduate solid state course that the crystal structure was certainly the low point, so I commend you for trying to improve on it. If I may suggest something, nowadays I quite like the periodic table in terms of crystal strucure (, and how a lot of materials of current interest (such as semimetals) have unusual lattices.

    Best regards,
    Cesar Uliana

    1. Dear Cesar,

      Thanks for the helpful comment.

      I think the discovery/development of x-ray crystallography was so important for 2 reasons.

      1. If you don't know the detailed atomic and crystal structure it is hard to explain most properties and start developing theory.

      2. It has become so crucial in other fields beyond condensed matter: mineralogy, chemistry, and structural biology. Practically, everything we know about molecular biology and protein function goes back to structural determinations from x-ray crystallography.

      However, I like your point about liquid helium. Without it we certainly would not have superconductivity or the understanding that comes from low-temperature studies.

      Furthermore, liquid helium has opened up whole new opportunities for chemistry and molecular biology because it enhances all sorts of instrumentation such as NMR, ESR (often using high field magnets).

      Certainly for quantum many-body physics, liquid helium was more important that x-ray crystallography.
      But, for all of science I would go with crystallography.

      Thanks for pointing out the periodic table. I will use it next year.