FIRST PRINCIPLES CALCULATIONS ON CRYSTALLINE AND LIQUID-IRON AT EARTHCORE CONDITIONS

Ab initio electronic structure calculations, based upon density functi onal theory within the generalised gradient approximation using ultras oft non-norm-conserving Vanderbilt pseudopotentials, have been used to predict the structure and properties of crystalline and liquid iron a nd solid FeSi at conditions found in the Earth's core. The quality of the pseudopotentials used was assessed by calculating well documented properties of the solid phase: we have accurately modelled the equatio n of state of bcc and hcp Fe and FeSi, the bcc --> hcp phase transitio n, the magnetic moment of bcc Fe, the elastic constants of bcc Fe, the bcc --> bct distortive phase transition and the phonon frequencies fo r fee Fe; the results show good agreement with both theory and experim ent. Simulations were also performed on liquid iron and we present the first ab initio quantum molecular dynamics calculations on the struct ure and transport properties of liquid iron under core conditions. Our calculations show that the structure of liquid iron at the conditions to be found in the outer core is highly compressed with a first-neigh bour coordination number inferred from the radial distribution functio n of ca. 12. We have also predicted a diffusion coefficient of 0.5 x 1 0(-4) cm(2) s(-1) indicative of a core viscosity of ca. 0.026 Pa s, in line with current estimates.