Atomic structures and magnetism in smallMoS2andWS2clusters

Abstract

First-principles calculations on stoichiometric ${\mathrm{Mo}}_n{\mathrm{S}}_{2n}$ and ${\mathrm{W}}_n{\mathrm{S}}_{2n}(n=1\text{–}8)$ clusters show that their lowest energy atomic structures are dominated by a central core of metal atoms while the S atoms cap this core. We discuss in detail terminal, edge, and face capping of tetrahedral and octahedral Mo clusters by sulfur atoms for off-stoichiometric compositions also. Capping on the terminal sites is found to be least favorable. Edge capped ${\mathrm{Mo}}_4{\mathrm{S}}_6$ and face capped ${\mathrm{Mo}}_6{\mathrm{S}}_8$ clusters have high symmetries and high stability among all the clusters we have studied. We find that magnetic isomers are lowest in energy for some clusters though bulk $M{\mathrm{S}}_2$ ($M=\mathrm{Mo}$ and W) is nonmagnetic. Our results on ${\mathrm{Mo}}_6{\mathrm{S}}_{8+p}(p=0\text{–}6)$ clusters further show that ${\mathrm{Mo}}_6{\mathrm{S}}_{12}$ is magic with $4{\mu }_B$ magnetic moment. The origin of magnetism and bonding nature in these clusters is discussed. Our finding could lead to the possibility of magnetic clusters of a variety of nonmagnetic transition-metal compounds and their interesting assemblies.