First principles study of electronic structure for cubane-like and ring-shaped structures of M4O4, M4S4 clusters (M = Mn, Fe, Co, Ni, Cu)

Spin-polarized DFT has been used to perform a comprehensive study of the geometric structures and electronic properties for isolated M4X4 nano-clusters between their two stable isomers - a planar rhombus-like 2D structure and a cubane-like 3D structure with M = Mn, Fe, Co, Ni, Cu ; X = O, S. These two structural patterns of the M4X4 clusters are commonly found as building blocks in several poly-nuclear transition metal complexes in inorganic chemistry. The effect of the van der Waals corrections to the physical properties have been considered in the electronic structure calculations employing the empirical Grimme's correction (DFT+D2). We report here an interesting trend in their relative structural stability - the isolated M4O4 clusters prefer to stabilize more in the planar structure, while the cubane-like 3D structure is more favourable for most of the isolated M4S4 clusters than their planar 2D counterparts. Our study reveals that this contrasting trend in the relative structural stability is expected to be driven by an interesting interplay between the s-d and p-d hybridization effects of the constituents' valence electrons.Comment: 10 pages, 6 figure

Structure, reactivity and electronic properties of V-doped Co clusters

Structures, physical and chemical properties of V doped Co$_{13}$ clusters have been studied in detail using density functional theory based first-principles method. We have found anomalous variation in stability of the doped clusters with increasing V concentration, which has been nicely demonstrated in terms of energetics and electronic properties of the clusters. Our study explains the nonmonotonic variation in reactivity of Co$_{13-m}$V$_m$ clusters towards H$_2$ molecules as reported experimentally [J. Phys. Chem. {\bf 94}, 2744 (1990)]. Moreover, it provides useful insight into the cluster geometry and chemically active sites on the cluster surface, which can help to design better catalytic processes.Comment: 10 pages, 9 figures, 4 table

Engineering the magnetic properties of the Mn13_{13} cluster by doping

With a goal to produce giant magnetic moment in Mn$_{13}$ cluster which will be useful for practical applications, we have considered the structure and magnetic properties of pure Mn$_{13}$ cluster and substitutionally doped it with X = Ti, V, Cr, Fe, Co, Ni atom to produce Mn$_{12}$X clusters. We find that Ti and V substitutions in Mn$_{13}$ cluster are the most promising in terms of gaining substantial binding energy as well as achieving higher magnetic moment through ferromagnetic alignment of atom-centered magnetic moments. This has been demonstrated in terms of energetics and electronic properties of the clusters. For comparison, we have also studied the effect of N-capping of Mn$_{13}$ cluster, predicted in the earlier work [Phys. Rev. Lett. {\bf 89}, 185504 (2002)] as a means to produce stable giant magnetic moment in Mn clusters upto cluster size of 5 Mn atoms.Comment: 8 pages, 9 figures, 2 table

Recursive approach to study transport properties of atomic wire

In this study, we propose a recursive approach to study the transport properties of atomic wires. It is based upon a real-space block-recursion technique with Landauer's formula being used to express the conductance as a scattering problem. To illustrate the method, we have applied it on a model system described by a single band tight-binding Hamiltonian. Results of our calculation therefore may be compared with the reported results on Na-atom wire. Upon tuning the tight-binding parameters, we can distinctly identify the controlling parameters responsible to decide the width as well as the phase of odd-even oscillations in the conductance.Comment: 9 pages, 8 figures, table

Ab initio study of structural stability of small 3dd late transition metal clusters : Interplay of magnetization and hybridization

Using first-principles density functional theory based calculations, we analyze the structural stability of small clusters of 3$d$ late transition metals. We consider the relative stability of the two structures - layer-like structure with hexagonal closed packed stacking and more compact structure of icosahedral symmetry. We find that the Co clusters show an unusual stability in hexagonal symmetry compared to the small clusters of other members which are found to stabilize in icosahedral symmetry based structure. Our study reveals that this is driven by the interplay between the magnetic energy gain and the gain in covalency through $s$-$d$ hybridization effect. Although we have focused our study primarily on clusters of size 19 atoms, we find that this behavior to be general for clusters having sizes between 15 and 20.Comment: 10 pages, 9 figures, work has been accepted in Phys. Rev. B (2011

Relative stability of zincblende and wurtzite structure in CdX(X = S, Se, Te) series - A NMTO study

Using NMTO-downfolding technique we have revisited the issue of relative stability between zincblende (ZB) and wurtzite (WZ) symmetries in case of CdS, CdSe and CdTe semiconductors. Our computed ionicity factors using accurate NMTO-downfolding successfully brings out the right trend within the CdX series - CdS being most ionic stabilizes in WZ symmetry while CdSe and CdTe being more covalent stabilizes in ZB symmetry. Our NMTO constructed Wannier functions corresponding to only valence bands provide a nice demonstration of this fact. The tendency towards ZB stability is governed by the covalency which prefers isotropic nature of the tetrahedral bonds.Comment: 13 pages, 6 figures, 4 table