Ballistic conductance calculations on infinite one-atom zigzag chains of Co and Au, and multi-atom Au nanowires, were computed using the Landauer-Biittiker formalism within the local-density approximation (LDA). In the cobalt case, the majority spin channel exhibits quantized conductance, but because of the close spacing of the d levels, the minority channel does not. The calculated conductance is somewhat larger than what is observed. We suggest that the discrepancy is an indication that the Landauer-Biittiker formalism breaks down in this narrow d band material. In contrast, Au (which was determined not to be spin polarized) does show well-behaved quantization in the case of the infinite zigzag chain. By increasing the dimension of the cross section of the chain, we find that quantization is lost once the lateral dimensions of the wire exceed two or so atoms. Finally, we show that the zigzag chain of Au can have a Peierls instability, making the chain insulating.
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