John P. Brodholt

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The temperature anomalies in the Earth's mantle associated with thermal convection can be inferred from seismic tomography, provided that the elastic properties of mantle minerals are known as a function of temperature at mantle pressures. At present, however, such information is difficult to obtain directly through laboratory experiments. We have therefore(More)
We consider three independent methodologies for calculating thermal equation of state (EOS) of the major earth-forming mineral, orthorhombic MgSiO3 perovskite: molecular dynamics (MD), lattice dynamics (LD) and Debye model (DM). Using the most recent developments in the GULP code, we derive a new interatomic potential, which is demonstrated to be extremely(More)
We have used high-temperature ab initio molecular dynamic simulations to study the equation of state of orthorhombic MgSiO3 perovskite under lower mantle pressure^temperature conditions. We have determined the Gru«neisen parameter, Q, as a function of volume. Our state-of-the-art simulations, accurate to within 10%, resolve the long-standing controversy on(More)
[1] We investigate the effect of pressure on the electronic spin state of ferric iron on Al-bearing MgSiO3-perovskite using first-principle computations. Ferric iron (6.25 mol%) and Al (6.25 mol%) substitute for Mg and Si respectively. Five substitution models on different atomic position pairs are examined. Our results show that spin state transition from(More)
The nature of the stable phase of iron in the Earth's solid inner core is still highly controversial. Laboratory experiments suggest the possibility of an uncharacterized phase transformation in iron at core conditions and seismological observations have indicated the possible presence of complex, inner-core layering. Theoretical studies currently suggest(More)
[1] The elastic constants of post-perovskite of chemical composition Mg0.9375Fe0.0625SiO3 and Mg0.8750Fe0.1250SiO3 have been calculated at 0 K and 136 GPa using ab initio methods. For both compositions studied, iron remains in a high-spin state below 180 GPa at 0 K. The effect of spin state on elastic properties is small. Logarithmic derivations of(More)
The themoelastic properties of Mg2SiO4 ringwoodite at mantle pressure and temperature conditions are reported based on ab nitio molecular dynamic simulations. A third-order Birch–Murnaghan equation at a reference temperature of 2000 K is defined by 0 = 138 GPa, K′ 0 = 5.2, and V0(2000 K) = 560.3 Å3. The Grűneisen parameter is determined to be γ(V) =(More)
Post-perovskite MgSiO(3) is believed to be present in the D'' region of the Earth's lowermost mantle. Its existence has been used to explain a number of seismic observations, such as the D'' reflector and the high degree of seismic anisotropy within the D'' layer. Ionic diffusion in post-perovskite controls its viscosity, which in turn controls the thermal(More)
In order to predict the stable polymorph of iron under core conditions, calculations have been performed on all the Ž . Ž . candidate phases proposed for inner core conditions, namely, body-centred cubic bcc , body-centred tetragonal bct , Ž . Ž . hexagonal close-packed hcp , double-hexagonal close-packed dhcp and an orthorhombically distorted hcp(More)
In this article we describe the eMinerals mini grid, which is now running in production mode. This is an integration of both compute and data components, the former build upon Condor, PBS and the functionality of Globus v2, and the latter being based on the combined use of the Storage Resource Broker and the CCLRC data portal. We describe how we have(More)