Correlation betweend-Band Occupancy and Crystal Structure in the Rare Earths

The rare-earth crystal structure sequence hcp^ Sm-type^ double-hcp^ fcc observed for decreasing atomic number and increasing pressure is quantitatively correlated with the d-band occupancy through the d-band energy contribution to the total energy. Self-consistent calculations show that the number of d electrons is very sensitive to the relative size of the ion core. The theory thus accounts for La's anomalous double-hcp structure and the apparent deviations from the electron-per-atom rules exhibited by certain rare-earth Laves phases.