Iron isotope fractionation between pyrite (FeS2), hematite (Fe2O3) and siderite (FeCO3): A first-principles density functional theory study

Blanchard, Marc; Poitrasson, Franck; Méheut, Merlin; Lazzeri, Michele; Mauri, Francesco; Balan, Etienne

doi:10.1016/j.gca.2009.07.034

Cited by 183 publications

(166 citation statements)

References 60 publications

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“…Polyakov et al 2007). First calculations applying equilibrium fractionations derived by ab initio methods have been published by Blanchard et al (2009) for Fe and by Rustad et al (2010) for Mg and Ca.…”

Section: 7mentioning

confidence: 99%

Theoretical and Experimental Principles

Hoefs

2015

Stable Isotope Geochemistry

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Isotopes are atoms whose nuclei contain the same number of protons but a different number of neutrons. The term "isotopes" is derived from Greek (meaning equal places) and indicates that isotopes occupy the same position in the periodic table.It is convenient to denote isotopes in the form m n E, where the super-script "m" denotes the mass number (i.e., sum of the number of protons and neutrons in the nucleus) and the subscript "n" denotes the atomic number of an element E. For example, 12 6 C is the isotope of carbon which has six protons and six neutrons in its nucleus. The atomic weight of each naturally occurring element is the average of the weights contributed by its various isotopes.Isotopes can be divided into two fundamental kinds, stable and unstable (radioactive) species. The number of stable isotopes is about 300; whilst over 1200 unstable ones have been discovered so far. The term "stable" is relative, depend-ing on the detection limits of radioactive decay times. In the range of atomic numbers from 1 (H) to 83 (Bi), stable nuclides of all masses except 5 and 8 are known. Only 21 elements are pure elements, in the sense that they have only one stable isotope. All other elements are mixtures of at least two isotopes. The relative abundance of different isotopes of an element may vary substantially. In copper, for example, 63 Cu accounts for 69 % and 65 Cu for 31 % of all copper nuclei. For the light elements, however, one isotope is predominant, the others being present only in trace amounts.The stability of nuclides is characterized by several important rules, two of which are briefly discussed here. The first is the so-called symmetry rule, which states that in a stable nuclide with low atomic number, the number of protons is approximately equal to the number of neutrons, or the neutron-to-proton ratio, N/Z, is approximately equal to unity. In stable nuclei with more than 20 protons or neutrons, the N/Z ratio is always greater than unity, with a maximum value of about 1.5 for the heaviest stable nuclei. The electrostatic Coulomb repulsion of the positively charged protons grows rapidly with increasing Z. To maintain the

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Section: 7mentioning

confidence: 99%

Theoretical and Experimental Principles

Hoefs

2015

Stable Isotope Geochemistry

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“…In order to interpret natural data measured in pyrite, they assumed that the β-factors for mackinawite would be similar to those for troilite, since both are Fe(II) monosulphides. Blanchard et al (2009) used first principle calculations (Schauble et al, 2001(Schauble et al, ,2006 to discuss the pyrite β-factors given by the technique from Polyakov and co-workers. Fig.…”

Section: Comparison With Calculated Predictionsmentioning

confidence: 99%

Experimental determination of the equilibrium Fe isotope fractionation between and FeSm (mackinawite) at 25 and 2°C

Guilbaud

Butler

Ellam

et al. 2011

Geochimica et Cosmochimica Acta

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“…There is good agreement between the frequencies computed by both implementations of DFT used, as well as with experimental data and previous DFT studies of the pyrite phase. 48,[52][53][54] The majority of the phonon frequencies for pyrite are lower than the corresponding experimental values, while for marcasite there is a more variable distribution.…”

Section: B Vibrational Contribution To the Energy Of Iron Disulfide mentioning

confidence: 99%

Density functional theory study of the relative stability of the iron disulfide polymorphs pyrite and marcasite

et al. 2010

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The performance of density functional theory (DFT) has been widely examined with regard to its ability to predict the properties of minerals, though less attention has been given to the correct determination of the relative stability of structurally similar polymorphs. Here a detailed examination is performed of the numerical and theoretical factors that may influence the structure and relative energetics of two such polymorphs of iron disulfide, namely pyrite and marcasite, within density functional theory. Both the local density approximation and commonly used generalized gradient approximation exchange-correlation functionals, such as PBE, are found to predict that marcasite is more stable than pyrite, at variance with experiment. Allowing for the zero point energy of vibration fails to remedy this discrepancy. While inclusion of a 2 sufficiently large Hubbard U parameter for iron is found to reverse the stability, this comes at the expense of a very poor description of other properties. Examination of three generalized gradient approximations developed specifically for the solid-state, namely AM05, Wu-Cohen and PBEsol, demonstrates that all of these functionals offer a superior description of the structures and relative energies of pyrite and marcasite through correctly predicting that the former is the ground state phase at ambient conditions.

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Iron isotope fractionation between pyrite (FeS2), hematite (Fe2O3) and siderite (FeCO3): A first-principles density functional theory study

Cited by 183 publications

References 60 publications

Theoretical and Experimental Principles

Theoretical and Experimental Principles

Experimental determination of the equilibrium Fe isotope fractionation between and FeSm (mackinawite) at 25 and 2°C

Density functional theory study of the relative stability of the iron disulfide polymorphs pyrite and marcasite

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