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 understand ing the physics behind these effects. In the present study this proble m has been approached using the example of the x-ray emission spectra of elemental Ni and Ni in Ni3Mo. The spectra were calculated within th e one-electron model on the basis of partial density of states obtaine d by various methods, namely the tight-binding method, the linear-muff in-tin-orbital method, and the method of local spherical waves. The co herent-potential-approximation method suitable for random materials wa s 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 di screpancy is not dependent on the method of calculation. For Ni3Mo, al l the considered methods provide the correct basic shape of the L(alph a) spectrum, and calculated spectra differ only in details of the inte nsity 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 t he correlation effects.