Tin clusters formed by fundamental units: a potential way to assemble tin nanowires

First-principles calculations using density functional theory (DFT) have been performed on Sn(n) clusters up to 561 atoms. The results show that thread-like structures based on the unit of Sn(15) are favored for n up to 60, and then a plate-like Sn(90) unit is preferred. The unique structures are explained by the strong covalent bonding character of Sn(15) units. Due to the weak binding forms among layers, plate-like stacked structures are less preferred than octahedral (O(h)) structures with n = 231. Besides, perfect icosahedral (I(h)) structures are always more favorable than O(h) isomers. The structural deviation of larger tin clusters from that of typical metal clusters may originate from the disparity in α/β tin bulk and more compact fcc bulk phases. Compared with the previous studies, we conclude that the weaker the bulk metallic character, the larger the nonmetal-metal transition size. After considering the van der Waals density functional (vdW-DF), we found that the average bond length of tin clusters becomes larger and more compact structures will be further stabilized. Our studies may provide some insight for experiments to assemble tin nanowires.