Structural and magnetic isomers ofM(BN)36andM4(BN)36clusters(M=Ti,V,Cr,Mn,Fe,Co,Ni,Cu): Anab initiodensity functional study

Abstract

Using the plane wave based pseudopotential method under the density functional formalism, the geometry and electronic structures of $M$ and ${M}_{4}$ encaged ${(\mathrm{B}\mathrm{N})}_{36}$ clusters have been investigated, where $M$ represents Ti, V, Cr, Mn, Fe, Co, Ni, and Cu atoms. The lowest energy structure of the $M{(\mathrm{B}\mathrm{N})}_{36}$ cluster shows that the impurity atom prefers to occupy either the center or off-center and close to the hexagonal ring of the cage. Geometry and electronic structures of ${M}_{4}$ clusters have been calculated in the bare state as well as inside the octahedral ${(\mathrm{B}\mathrm{N})}_{36}$ cluster. For free ${M}_{4}$ clusters, except ${\mathrm{Cu}}_{4}$, which forms a planar rhombus structure, all other tetramer clusters adopt three dimensional bent rhombus or tetrahedron configuration. In sharp contrast, the equilibrium structure of ${M}_{4}$ clusters inside the ${(\mathrm{B}\mathrm{N})}_{36}$ cage results in significant deformation in comparison to that in the free state. Unlike others, it is found that the stability of ${\mathrm{V}}_{4}$, ${\mathrm{Fe}}_{4}$, ${\mathrm{Co}}_{4}$, and ${\mathrm{Ni}}_{4}$ tetramers have been enhanced inside the cage. Importantly, these small clusters are found to retain their magnetic nature even after encaging them inside the ${(\mathrm{B}\mathrm{N})}_{36}$ cluster. In general, the magnetic moment of the ${M}_{4}$ clusters are found to decrease inside the ${(\mathrm{B}\mathrm{N})}_{36}$ cage, except that for ${\mathrm{Cr}}_{4}$ cluster, which showed significant increase in the magnetic moment. The electronic density of state analysis of these systems shows additional electronic states in the large gap of ${(\mathrm{B}\mathrm{N})}_{36}$ cluster originated by the $M$ atoms or ${M}_{4}$ clusters.