Ab Initio Simulations of Transition Metal Alloys: Towards the Multiscale Modeling

Sammanfattning: The present thesis concerns applications of first principles electronic structure calculations in conjunction with methods of statistical mechanics for simulations of transition metal alloys both in the bulk and at surfaces.A fully relativistic generalization of the exact muffin-tin orbitals (EMTO) method has been developed. The method accurately takes into account spin-orbit coupling and allows one to calculate orbital polarization and magneto-crystalline anisotropy in magnetic systems as well as increasing the range of applicability of the EMTO method to heavy elements. A new direct-exchange Monte Carlo (DEMC) method has been proposed, which is capable to tackling effectively statistical simulations of surface segregations in disordered and ordered alloys.The applications of relativistic methods include calculations of spin and orbital magnetization in iron-cobalt disordered and partially ordered alloys, as well as computation of the core-level shifts (CLS) in transition metal alloys. It has been found, that relativistic corrections are important for CLS calculations in 5-d metal alloys. Properties of a Ni monolayer deposited on a Cu surface have been studied. The monolayer is found to be unstable in the top layer, and its magnetization depends greatly on the surface orientation. Two distinct energy levels have been found to exist Co/Cu/Ni trilayers deposited on the (100) Cu surface, which correspond to a completely paramagnetic trilayer and the case when only Ni is paramagnetic.Vacancy ordering in substoichometric titanium carbides TiCx have been simulated. Existence of three ordered phases in the range of carbon concentration x=0.5 ÷1.0 has been revealed and a theoretical phase diagram has been proposed. Surface segregations have been calculated in disordered Ni50Pt50 and Ni50Pd50 as well as in ordered NiPt alloys. Segregation reversal has been observed in the Ni50Pt50 alloy with Pt segregation at the (111) surface and Ni segregation at the (110). In the ordered NiPt alloys segregation behaviour is found to be affected greatly by small deviations from the exact stoichiometric composition in bulk. Surface magnetization in PdV and MoV bcc alloys have been studied. It has been found, that in PdV alloys surface segregations suppress magnetic order at the surface, while in MoV alloys magnetization is substantially enhanced due to the segregation.