The SPOCK equation of state for condensed phases under arbitrary compression

SUMMARY This short paper presents a new equation of state for condensed phases. The equation of state is built on the premise that $K^{\prime }$, the first derivative of the bulk modulus, monotonically increases with volume according to a power law. The input parameters are the zero-pressure volume $V_0$, bulk modulus $K_0$, and first and second derivatives of the bulk modulus, $K^{\prime }_0$ and $K^{\prime \prime }_0$ and also $K^{\prime }_{\infty }$, the value of $K^{\prime }$ at infinite compression. Expressions are provided for the internal energy, pressure, and bulk modulus. The equation of state is robust for all compressions as long as $K^{\prime \prime }_0 < 0$ and $K^{\prime }_{\infty } < K^{\prime }_0$. Heuristic values are suggested for situations in which available data is not sufficient to independently constrain $K^{\prime \prime }_0$ and $K^{\prime }_{\infty }$. The equation of state compares favourably with other equations of state using recently published experimental data on Au and Pt.