Parallelohedra, old and new.

It is shown that from a skewed, skeletal (edges and vertices), truncated octahedron, skewed skeletons can be derived of the other four convex parallelohedra found by Fedorov in 1885. In addition, three new nonconvex parallelohedra are produced, a counterexample to a statement by Grünbaum. This opens several new ways to view atomic positions in crystals, and new avenues in geometry.

Crystalline variational methods.

A surface free energy function is defined to be crystalline if its Wulff shape (the equilibrium crystal shape) is a polyhedron. All the questions that one considers for the area functional, where the surface free energy per unit area is 1 for all normal directions, can be considered for crystalline surface free energies. Such questions are interesting for both mathematical and physical reasons.