Ab initio calculations of partial molar properties in the single-site approximation

Abstract

We discuss the application of the single-site approximation in calculations of partial molar quantities, e.g., impurity solution energy, segregation energy, and effective chemical potential, which are related to a variation of the composition of an alloy or its nonequivalent parts. We demonstrate that these quantities may be considerably in error if they are obtained in methods based on the single-site approximation for fixed alloy compositions. This error does not reflect a breakdown but rather an inappropriate use of the single-site approximation which is, in fact, found to be sufficiently accurate when properly applied in calculations of partial molar quantities. ͓S0163-1829͑97͒03713-2͔

First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids

“…Note that CPA is very well suited for calculating partial molar properties, such as the GTCP in Eq. (2) [60]. In the demonstrations of the different shifts as average properties of volume and composition over substitutionally disordered fcc AgPd alloys in this work, the methodology is the same as in [18], however using LDA in all computational steps.…”

Surface segregation energies in transition-metal alloys

“…As a result, the chemical potentials and segregation energies may be obtained correctly in the single-site approximation. 31 The second important correction to the electrostatic potential and energy in the surface calculations is the monopole contribution to the ASA potential from the higher multipole moments of the charge density and the corresponding multipole-multipole contributions to the interatomic part of the Madelung energy. The inclusion of these terms, i.e., beyond the monopole-dipole contributions, may be viewed as the first step towards the full charge-density ͑FCD͒ technique.…”

“…For this reason and because Drchal and co-workers do not list surface segregation energies we will not consider their calculations here but refer to Ref. 31 where a discussion of the accuracy of the GPM is presented and to Ref. 32 where a discussion of their results for the RhPt alloy system may be found.…”

“…30 These authors rely on the general perturbation method ͑GPM͒ which completely neglects the renormalization of the host effective medium and therefore, as shown in Ref. 31, may lead to surface concentration profiles which are not only quantitatively but also qualitatively incorrect. For this reason and because Drchal and co-workers do not list surface segregation energies we will not consider their calculations here but refer to Ref.…”

Bulk ordering and surface segregation inNi50Pt50

“…43 Thus the on-site interactions, V (1) , which are needed for the surface segregation calculations must be obtained in direct total energy calculations for alloys with different compositions. In this work we have used the KKR-CPA-ASAM surface Green's-function method 19,20,30 to obtain V (1) ϪV bulk (1) .…”