An investigation of the relative stabilities and equations of state of possible Fe(3)S polymorphs was conducted using first-principles pseudopotential calculations. These calculations were based on density functional theory and performed using ultrasoft Vanderbilt pseudopotentials within the generalized gradient approximation. In accord with experiment, we found that the tetragonal Fe(3)P-type polymorph is the only stable phase along the 0 K isotherm as a function of pressure. Fe3S exhibits permanent magnetism at ambient conditions (Fei et al., 2000), but magnetism is suppressed by pressure and temperature, and therefore non-magnetic data are appropriate ones to use for modelling planetary interiors. For this reason, and because the Fe(3)P-type polymorph of Fe(3)S contains 32 atoms per unit cell it was impractical to incorporate magnetic properties into the simulations of this phase, we studied the behaviour of the non-magnetic phase. We obtained values of 250 GPa for the bulk modulus, K(0), and 4.61 for its first derivative with respect to pressure, K(0)', by fitting a 3(rd) order Birch-Murnaghan equation of state to the calculated internal energy as a function of volume for the non-magnetic Fe(3)P-type Fe(3)S. This suggests that a pressure far greater than that expected in the Martian interior would be needed to achieve a density comparable to that of the Martian core. We therefore conclude that it is unlikely that the core of Mars contains significant amounts of solid Fe(3)S.

An ab initio study of the relative stabilities and equations of state of Fe(3)S polymorphs / Martin, P; Vocadlo, L; Alfe, D; Price, Gd. - In: MINERALOGICAL MAGAZINE. - ISSN 0026-461X. - 68:5(2004), pp. 813-817. [10.1180/0026461046850221]

An ab initio study of the relative stabilities and equations of state of Fe(3)S polymorphs

Alfe D;
2004

Abstract

An investigation of the relative stabilities and equations of state of possible Fe(3)S polymorphs was conducted using first-principles pseudopotential calculations. These calculations were based on density functional theory and performed using ultrasoft Vanderbilt pseudopotentials within the generalized gradient approximation. In accord with experiment, we found that the tetragonal Fe(3)P-type polymorph is the only stable phase along the 0 K isotherm as a function of pressure. Fe3S exhibits permanent magnetism at ambient conditions (Fei et al., 2000), but magnetism is suppressed by pressure and temperature, and therefore non-magnetic data are appropriate ones to use for modelling planetary interiors. For this reason, and because the Fe(3)P-type polymorph of Fe(3)S contains 32 atoms per unit cell it was impractical to incorporate magnetic properties into the simulations of this phase, we studied the behaviour of the non-magnetic phase. We obtained values of 250 GPa for the bulk modulus, K(0), and 4.61 for its first derivative with respect to pressure, K(0)', by fitting a 3(rd) order Birch-Murnaghan equation of state to the calculated internal energy as a function of volume for the non-magnetic Fe(3)P-type Fe(3)S. This suggests that a pressure far greater than that expected in the Martian interior would be needed to achieve a density comparable to that of the Martian core. We therefore conclude that it is unlikely that the core of Mars contains significant amounts of solid Fe(3)S.
2004
An ab initio study of the relative stabilities and equations of state of Fe(3)S polymorphs / Martin, P; Vocadlo, L; Alfe, D; Price, Gd. - In: MINERALOGICAL MAGAZINE. - ISSN 0026-461X. - 68:5(2004), pp. 813-817. [10.1180/0026461046850221]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/753178
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