The electronic structure of the (001) surface of ordered low-temperature 50% Cu-Au alloy (CuAu I) with different surface compositions is investigated by using the tight-binding linearized muffin-tin orbital method. The charge distribution and the charge transfer of the CuAu I(001) surface are considered from various viewpoints. The calculated local density of states is compared with spectroscopic measurements. It is shown that the surface effect in the valence band photoemission spectrum of CuAu I could improve the agreement between theoretical and experimental spectra. Implications in surface physics and surface chemistry of the activation or deactivation of certain regions of the electronic energy spectrum of a surface by adjusting the temperature of the system are discussed.