Stampfl, C., Kambe, K., Fasel, R., Aebi, P., & Scheffler, M. (1998). Theoretical analysis of the electronic structure of the stable and metastable c(2x2) phases of Na on Al(001): Comparison with angle-resolved ultraviolet photoemission spectra. Physical Review B, 57(24), 15251-15260. doi:10.1103/PhysRevB.57.15251.