Under the Gradient Approximation （GGA）, the relaxed structures and electronic properties have been investigated for Cu nanowires with cross-sections of 3×3、5×5、7×7、9×9 and 11×11 atom layers by using the first-principles Projector Augmented Wave (PAW) potential within Density Function Theory (DFT) . For all the five-size nanowires, the relaxed structures still have four-fold symmetry. The vanishing of the neighbor atoms outside nanowire not only causes an enhance interactions between the surface atoms as well as the surface atoms and their first nearest neighbor atoms, but also drives the most electrons of the surface atoms to range in the higher energy region of the occupancy states.

Cu nanowires; relaxation; electronic property; first-principle