Compression curves of transition metals in the Mbar range: Experiments and projector augmented-wave calculations

The ambient temperature equations of state (EoS) of iron, cobalt, nickel, zinc, molybdenum, and silver have been measured by x-ray diffraction. These transition metals were compressed using diamond anvil cells with a helium pressure transmitting medium. The maximum pressure reached during these experiments varied between 65 GPa (for cobalt) and 200 GPa (for iron). This work completes previous measurements on six other metals [Phys. Rev. B 70, 094112 (2004)] to quantify the differences between ab initio calculations and experiment on a large experimental set of transition metals. The compression curves of iron, cobalt, nickel, zinc, molybdenum, silver, platinum, and gold are also calculated ab initio within the density-functional theory (DFT) formalism using the projector augmented-wave (PAW) method and different exchange-correlation functionals (LDA, GGA-PBE, GGA-PBEsol). The difference between PAW and available all-electron calculations is found to be negligible up to very high pressures. The success of each exchange-correlation functional is correlated with the atomic number. For all metals, the bulk modulus becomes overestimated at high pressure. In addition, this extended data set of metals' EoS enables to reduce further, but marginally, the systematic uncertainty of the high-pressure metrology based on the ruby standard.