First-Principles Calculations of Atomic Correlations in Metallic Alloys

Pinski：这项理论更新资助的重点是金属合金中原子相关性的第一性原理计算。对于铁镍合金，现有的理论和计算机代码将用于计算这些合金的几种性质，包括总能量作为体积和磁性排列的函数，以及原子的短程有序。虽然目前的理论在相图的富镍区应该是足够的，但在富铁端需要考虑原子位移的影响。对于含镍约为37%的铁镍合金（INVAR），其许多性能随温度、压力或磁场的变化而表现出异常行为。这种行为与强磁体积耦合有关。当前的计算代码将扩展到包括这些效果。通过将计算得到的直接相关函数用于一阶相变理论，可以提高其效用。目前的方法着眼于随机合金对具有无穷小振幅的浓度波的不稳定性，因此只给出了可能的二阶跃迁的指示。由于大多数合金转变都是一阶的，因此将使用密度泛函理论来计算共存区。一个计算密集型的程序将研究原子相关性对金属合金——特别是铁镍合金——性能的影响。这些最先进的计算将为理解这类重要材料的行为提供新的见解。此外，基本的见解将获得合金的相行为一般。＊＊＊

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. ***