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SIA formation energies in Fe

SIA formation energies in Fe. US-PP vs. PAW in VASP. Pär Olsson Dept. of Neutron Research Uppsala University. <100> projection. A Swedish ice cream brand. Ok, that was five abbreviations in one sentence. 1) SIA – Self Interstitial Atom.

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SIA formation energies in Fe

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  1. SIA formation energies in Fe US-PP vs. PAW in VASP Pär Olsson Dept. of Neutron Research Uppsala University The 4th workshop on multi-scale modelling of Fe-Cr

  2. <100> projection A Swedish ice cream brand Ok, that was five abbreviations in one sentence... • 1) SIA – Self Interstitial Atom An atom that is crowded in on others of the same kind. • US-PP – Ultrasoft • Pseudo Potentitial A soft pseudo potential acts on a pseudo wave function which is only exact outside a core radius. The 4th workshop on multi-scale modelling of Fe-Cr

  3. Ok, that was five abbreviations in one sentence... • 4) PAW – Projector Augmented Wave A linear transformation from the pseudo to the AE wave functions. 5) VASP – Vienna Ab initio Simulation Package A total energy code written by G. Kresse and J. Furthmüller, able to use both US-PP and PAW formalisms. The 4th workshop on multi-scale modelling of Fe-Cr

  4. US-PP Complete database available. Proven good for most solids. Implemented in many codes. Very fast. PAW Complete database available. Better accuracy for some elements. Not implemented in many codes. As fast as the US-PP. US-PP vs. PAW • Availability: • Reliability: • Versatility: The 4th workshop on multi-scale modelling of Fe-Cr

  5. How do they differ? • Kresse and Joubert have shown that the US-PP method can be derived from the PAW method by linearisation of two terms. • The PAW method is equivalent to an exact AE frozen core method. In the US-PP there are approximations. • PAW is better for magnetic materials, alkali and alkali earth elements, as well as for early 3d elements (Sc, Ti, V, Cr?). The 4th workshop on multi-scale modelling of Fe-Cr

  6. Example: ferromagnetic bcc Fe The 4th workshop on multi-scale modelling of Fe-Cr

  7. Why do I care? • C. Domain performed calculations with the US-PP method which display very interesting properties of both pure Fe SIAs and mixed Fe-Cr SIAs. • The PAW method is argued to give a better description of magnetic materials (such as bcc Fe) and early 3d elements (such as Cr). The 4th workshop on multi-scale modelling of Fe-Cr

  8. This study • Redo the US-PP calculations, using the PAW method. • (Pure Fe almost complete) • Check whether noncollinear magnetism has an effect on the pure Fe system. • (In progress) : Actually, crashing on me just before I wrote this.) The 4th workshop on multi-scale modelling of Fe-Cr

  9. Results (pure Fe) The 4th workshop on multi-scale modelling of Fe-Cr

  10. Noncollinear magnetism In the collinear US-PP and PAW cases, the local magnetic moments on the SIA atoms are very small. Hobbs et al has shown that an Fe pentamer has a noncollinear magnetic groundstate. The 4th workshop on multi-scale modelling of Fe-Cr

  11. Conclusion • So far, the difference for SIA energies in pure Fe between the US-PP and PAW methods is only in absolute values. • Noncollinear effects in bulk? • Interaction between Fe and Cr? • (computer) time will tell... The 4th workshop on multi-scale modelling of Fe-Cr

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