Energy dispersions and bandwidth in Pd 4d photoemission spectra

Atomic and electronic structures of a Pd(111) single crystal and a polycrystalline Pd film have been investigated by using low-energy electron diffraction (LEED) and photoemission spectroscopy (PES). LEED patterns of a clean Pd(111) show a threefold symmetry, suggesting no surface reconstruction. Band structures of Pd(111) for k(1) along the <(Gamma)over bar>-(M) over bar', <(Gamma)over bar>-(M) over bar, and <(Gamma)over bar>-(M) over bar symmetry lines have been determined experimentally from angle-resolved photoemission spectroscopy measurements and compared to those calculated within the local-density-functional approximation (LDA). The valence band PES spectrum of Pd film is also obtained and compared to the calculated 4d angular momentum projected local density of states within LDA. Experimental and LDA band structures of Pd(111) exhibit a reasonably good agreement, whereas experimental bandwidths are narrower than the LDA bulk bandwidths by 0.5-1 eV. Such a discrepancy can be improved theoretically by taking into account more localized Pd surface states. Tn contrast, the calculated Pd 4d quasiparticle spectral density by including the on-site Coulomb correlation cannot resolve the disagreement between PES and LDA, suggesting that the Coulomb correlation effect is not substantial in understanding PES spectra of Pd. [S0163-1829(97)01540-3].