Elastic constants and mechanical properties of Iron under extreme conditions

We have carried out molecular dynamics simulations of Iron under extreme pressure and temperature conditions close to the inner core of the Earth. Both bcc and hcp phases might be possible, and in this case we focus on hcp Fe. We use LAMMPS, with EAM interactions fit to the core conditions, to obtain mechanical properties. Our samples contain 1-2 million atoms, simulated during several ns. Using equilibrium molecular dynamics elastic constants Cij, are evaluated for a matrix in the pressure-temperature space, and used to obtain density, shear modulus, sound velocities, and yield strength. Results are compared with values from several constitutive models, DFT simulations and experimental results, obtaining reasonably good agreement with our results. We also carried out non-equilibrium simulations, applying shear to samples equilibrated at different pressures and temperatures, to obtain flow stress. We also calculated flow stress for uniaxially compressed samples and found that the flow stress is lower for samples compressed along [111] than for samples compressed along [001].