Thermal Ellipsoids

Splashery stretches a drumhead over this Splash's outline, twelve inches across, and finds the ways it can ring. Its lowest is 2254.1 Hz, 828 cents sharp of F6, the nearest tine on the comb. The next fifteen are its overtones, and each one draws its own figure: sand gathers on the lines that stay still.

Tap to make the atoms jiggle. Zoom in, then tap an atom to look there. Open your own CIF in the Splash tab.

Crystallography describes an atom's average position and spread with a displacement tensor. An ellipsoid is a Gaussian picture of that spread, which can include vibration and static disorder; its long axis shows the direction of greatest spread. It is not a photograph of an atom's motion.

Pick one of 41 measured structures in seven groups (everyday molecules, medicines, molecules of life, minerals and gems, ice and salts, proteins, and DNA and RNA) from the Crystallography Open Database or the Protein Data Bank, or open a CIF, mmCIF or PDB file. Show fills the unit cell with the atoms' symmetry copies, as minerals show by default. Probability sets the ellipsoid to enclose 30%, 50% or 90% of the spread; hard minerals and cold crystals have small ones. Draw solid ellipsoids or one Gaussian per atom, with or without bonds; hydrogens can be small spheres, as refined, or hidden. Tap to jiggle; zoom in, then tap an atom to focus there. Files stay on your device. Use it to explore, not to measure.

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