  We present temperature dependent inelastic neutron scattering measurments,
accompanied byab-initio calculations of phonon spectra and elastic properties
as a function of pressure to understand anharmonicity of phonons and to study
the mechanism of negative thermal expansion and negative linear compressibility
behaviour of ZnAu2(CN)4. The mechanism is identified in terms of specific
anharmonic modes that involve bending of the Zn(CN)4-Au- Zn(CN)4 linkage. The
high-pressure phase transition at about 2 GPa is also investigated and found to
be related to softening of a phonon mode at the L-point at the Brillouin zone
boundary and its coupling with a zone-centre phonon and an M-point phonon in
the ambient pressure phase. Although the phase transition is primarily driven
by a L-point soft phonon mode, which usually leads to a second order transition
with a 2 x 2 x 2 supercell, in the present case the structure is close to an
elastic instability that leads to a weakly first order transition.
