Spinodal equation of state for rutile ${\mathrm{TiO}}_2$

We present a general computational scheme to extend the spinodal equation of state [García Baonza et al., Phys. Rev. B 51, 28 (1995)] to the interpretation of the cell parameters response to hydrostatic pressure in orthogonal lattices. As an important example, we analyze the pressure $\mathrm{}\left(p\right)\mathrm{}$–volume $\mathrm{}\left(V\right)\mathrm{}$–temperature (T) data of the rutile phase of ${\mathrm{TiO}}_2.$ We show that results of ab initio perturbed ion calculations and very recent x-ray-diffraction experiments of isothermal compression on this system closely follow the spinodal conduct. The computational scheme permits the incorporation of temperature effects in the static calculation as well as in the room-temperature experimental data. Overall, we find highly consistent results and good theory-experiment agreement for a significant series of observables, including structural parameters, $p-V$ diagram, bulk modulus, linear compressibilities, and thermal-expansion coefficient. The observed discrepancies in the pressure first derivative of the bulk modulus can be traced back to the difference between the theoretical and the experimental spinodal pressure.