The structural and dynamic properties of the mineral Cooperite (PtS) are investigated using density-functional theory. The results show that a competition with the less symmetric but more compact PdS structure leads to a phase transition when the pressure is increased. However, before the phase transition, PtS displays a rare anomalous elastic behavior by expanding along its long axis under hydrostatic pressure. We report the elastic constants of PtS and interpret this negative linear compressibility in the context of a displacive phase transition. We also show that the real structure of PtS is less symmetric than originally determined by experiment.
Marmier, A., Ntoahae, P. S., Ngoepe, P. E., Pettifor, D. G., & Parker, S. C. (2010). Negative compressibility in platinum sulfide using density-functional theory. Physical Review B, 81(17), . https://doi.org/10.1103/PhysRevB.81.172102