Exact solution of a Four-Site d-Electron Problem: The nickel-metal photoemission spectrum

Exact calculated results for the nickel density of electron states, as would be measured in valence-band photoemission, are presented. A realistic local-density-approximation one-electron structure, sampled at four wave vectors, and an intrasite electron-electron interaction of full generality are used. This new approach to the Ni photoemission problem yields accurately the experimental bandwidth, exchange splitting, satellite position, and relative intensities. Physical conclusions about the true Ni many-body states are drawn.