The density of $\varepsilon$-iron has been calculated at pressures and temperatures up to 300 GPa and 1300 K, respectively. We observe $\varepsilon$ to $\beta$ phase transition at pressures between 135 and 300 GPa and temperature above 1350 K; the pattern can be interpreted in terms of double hexagonal close-packed structure. The density calculated at high pressure and temperature (330–360 GPa and 5000–7000 K) closely matches with preliminary reference Earth model density, thereby imposing constraint on the composition of the Earth's inner core.

• Received 3 December 1998

DOI:https://doi.org/10.1103/PhysRevLett.84.1720