Ab-initio calculations of negative thermal expansion in ZrW2O8

Here we report ab-initio phonon calculations in cubic phase of ZrW2O8 to understand its negative thermal expansion (NTE) behaviour. We found that the response of phonon modes to the external pressure and temperature are very different, while both the thermodynamical conditions lead to highly anharmonic phonons, The pressure dependence anharmonicity is responsible for NTE. The calculations are able to reproduce the experimentally observed anomalous trends, namely, the softening of the low frequency peak at about 4 MeV in the phonon spectra with pressure and its hardening with temperature, while both the changes involve a compression of the lattice. (author)