Exotic physical properties of matter studied by simulation

Martin Dove
Queen Mary University. London

Over the past two decades experimental work has identified materials that
shrink when heated, and get softer when compressed. These and other related
properties appear, at least from an admittedly limited set of data, to be
linked. Recently we have explored a number of these materials based largely
on simulations of phonon spectra of various examples, coupled with models
based on structure flexibility. We show how negative thermal expansion and
pressure-induced softness arise together as an inevitable consequence of the
flexibility of the structure. We also expose a new and possibly common
mechanism for negative thermal expansion based on the role of acoustic
modes. The role of phonon anharmonicity is also explored. I would claim that
we are still on the route towards understanding these materials, but from a
physics perspective we are making real progress.