We have used first-principles linear muffin-tin orbital (LMTO) electronic structure calculations in the atomic sphere approximation (ASA), implemented directly in real space (RS) to investigate theoretically the behavior of the isomer shift of substitutional Fe impurities in metallic hosts. We find that the isomer shift in these systems is dominated by the 4$s$ contribution at the Fe site. Since both the volume occupied by the impurity and the valence of the metallic host vary widely in the systems studied here, the influence of these factors on the isomer shift could be investigated. When RS-LMTO-ASA basis functions are used, a simple picture emerges, which allows us to understand the observed trends of the isomer shift in terms of two quantities: the number of 4$s$ electrons at the impurity site and the probability of finding one of these electrons close to the nucleus. We find that probability follows a nearly universal curve as a function of the volume occupied by the impurity in the host, which leads to more negative isomer shift values as the Fe is compressed into smaller volumes. The number of 4$s$ electrons at the Fe site depends both on the volume occupied by the impurity in the host and on the host valence. Our approach can partially deconvolute these dependences, calling attention to the interesting processes which regulate the isomer shift trends.

• Received 28 April 1997

DOI:https://doi.org/10.1103/PhysRevB.56.13035