Ionization Energies of Niobium Carbide Clusters NbnCm (n = 3−10, m = 0−7)

Investigation of Structures, Stabilities, and Electronic and Magnetic Properties of Niobium Carbon Clusters Nb7Cn (n = 1-7)

The geometrical structures, relative stabilities, and electronic and magnetic properties of niobium carbon clusters, Nb7Cn (n = 1-7), are investigated in this study. Density functional theory (DFT) calculations, coupled with the Saunders Kick global search, are conducted to explore the structural properties of Nb7Cn (n = 1-7). The results regarding the average binding energy, second-order difference energy, dissociation energy, HOMO-LUMO gap, and chemical hardness highlight the robust stability of Nb7C3. Analysis of the density of states suggests that the molecular orbitals of Nb7Cn primarily consist of orbitals from the transition metal Nb, with minimal involvement of C atoms. Spin density and natural population analysis reveal that the total magnetic moment of Nb7Cn predominantly resides on the Nb atoms. The contribution of Nb atoms to the total magnetic moment stems mainly from the 4d orbital, followed by the 5p, 5s, and 6s orbitals.

Ti12C68: A stable T h -symmetry hollow cage

A stable T h -symmetry Ti12C68 cage was systemically investigated using density functional theory. The structure of Ti12C68 is a hollow cage with twelve TiC13 subunit of three pentagons and one hexagon. The calculated frequencies are in the range 95.1 cm-1-1423.9 cm-1. There are no imaginary frequencies, showing its kinetic stability. Ab initio molecular dynamics simulations demonstrate that the topological structure of cage-like Ti12C68 cluster was well maintained when the effective temperature is up to 1139 K. The natural bond orbitals analysis shows that the d orbit of Ti atoms form four σ bonds with the neighboring four carbon atoms in each TiC13 subunit playing an important role in the cluster stability. The molecular frontier orbitals analysis indicates that Ti12C68 cage has a narrow HOMO-LUMO gap with metal-like property. It would be expected to enrich the species of hollow metal carbide clusters.