9531223 Pinski This theoretical renewal grant focuses on first-principles calculations of atomic correlations in metallic alloys. For iron-nickel alloys, existing theories and computer codes will be used to calculate several properties of these alloys including the total energy as a function of volume and magnetic arrangement, and atomic short-range order. While currrent theories should be sufficient in the nickel-rich region of the phase diagram, the effect of atomic displacements needs to be included for the iron-rich end. For iron-nickel alloys with about thirty-seven percent nickel (INVAR), many properties have anomalous behavior as a function of temperature, pressure or magnetic field. This behavior has been linked to strong magneto-volume coupling. Current computational codes will be extended to include these effects. The utility of the calculated direct-correlation function can be increased by its use in a theory of first-order phase transitions. The current approach looks at the instability of the random alloy to a concentration wave with an infinitesimal amplitude and therefore only gives indication of possible second-order transitions. Since most alloy transitions are first-order, density functional theory will be used to calculate the coexistence region. %%% A computationally-intensive program will investigate the effects of atomic correlations on the properties of metallic alloys - in particular, iron-nickel alloys. These state-of- the-art calculations will yield new insight to understanding the behavior of this important class of materials. In addition, fundamental insight will be gained into the phase behavior of alloys in general. ***
