CORRELATION-EFFECTS IN X-RAY-SPECTRA OF NI AND NI IN NI3MO

An estimation of factors which can cause significant many-body effects in x-ray spectra of a given material is very important for understanding the physics behind these effects. In the present study this problem has been approached using the example of the x-ray emission spectra of elemental Ni and Ni in Ni3Mo. The spectra were calculated within the one-electron model on the basis of partial density of states obtained by various methods, namely the tight-binding method, the linear-muffin-tin-orbital method, and the method of local spherical waves. The coherent-potential-approximation method suitable for random materials was additionally considered for Ni3Mo. In the case of elemental Ni, the one-electron model fails and all applied methods result in an emission spectrum about 1.2 eV broader than the experimental spectrum. This discrepancy is not dependent on the method of calculation. For Ni3Mo, all the considered methods provide the correct basic shape of the L(alpha) spectrum, and calculated spectra differ only in details of the intensity distribution. The addition of a second element (Mo) leads to the increase of the Ni-Ni distance that results in reduction of the many-body effects. The observed broadening of the Ni spectra from Ni3Mo as compared with the spectrum of elemental Ni is due to the decrease of the correlation effects.