Evolution of the Spin Magnetic Moments and Atomic Valence of Vanadium in Vanadium doped Copper, Silver, and Gold Clusters.*

The atomic structures, bonding characteristics, spin magnetic moments, and stability of VCu$_{\mathrm{x}}^{\mathrm{+}}$, VAg$_{\mathrm{x}}^{\mathrm{+}}$, and VAu$_{\mathrm{x}}^{\mathrm{+}}$ (x $=$ 3 - 14) clusters have been examined using density functional theory. Our studies indicate that the effective valence of vanadium is size-dependent and at small sizes some the valence electrons of vanadium are localized on vanadium while at larger sizes the 3$d$ orbitals of the vanadium participate in metallic bonding eventually quenching the spin magnetic moment. The electronic stability of the clusters may be understood through a split-shell model that partitions the valence electrons in either a delocalized shell or localized on the vanadium atom. A molecular orbital analysis reveals that in planar clusters the delocalization of the 3d orbital of vanadium is enhanced when surrounded by gold due to enhanced \textit{6s-5d} hybridization. Once the clusters become three-dimensional, this hybridization is reduced and copper most readily delocalizes the vanadium's valence electrons. By understanding these unique features, greater insight is offered into the role of a host materials electronic structure in determining the bonding characteristics and stability of localized spin magnetic moments in quantum confined systems.