First Principles Calculations for Structural, Electronic, and Magnetic Properties of Gadolinium-Doped Alumina Clusters

Atomic structures and physical properties of Gd-doped alumina clustersnamely, GdAl_{2<i>n</i>–1}O_3<i>n</i> and Gd₂Al_{2<i>n</i>–2}O_3<i>n</i> with <i>n</i> = 1–10have been studied within the framework of spin-polarized density functional theory and the projector augmented wave pseudopotential method. We find that the atomic structures of the host clusters (Al₂O₃)_<i>n</i> are not changed significantly by the substitutional doping of a Gd atom on Al sites. Our results show that in the size range of the clusters we studied, a Gd atom prefers a maximum 4-fold-coordinated Al-site, except for <i>n</i> = 8, in which a 5-fold-coordinated Al site is favored. The substitution of Al with Gd atom is energetically favorable. This is in contrast to the substitutional doping of Gd in the bulk alumina corundum structure that is endothermic. There is a net magnetic moment of 7 μ_B per Gd atom, which is mostly localized on the Gd atom. Further substitution of an Al atom with Gd in GdAl_{2<i>n</i>–1}O_3<i>n</i> clusters results in the lowest-energy configuration's being either ferromagnetic or antiferromagnetic, the difference between the two magnetic states being very small. The variation in the magnetic state is found to be associated with the variation in the coordination number of Gd atoms and the sites of the two Gd atoms. Our results suggest that Gd doping of nanoparticles offers an interesting way to prepare Gd-doped ceramic materials

Electronic Origin of the Stability of Transition-Metal-Doped B₁₄ Drum-Shaped Boron Clusters and Their Assembly into a Nanotube

We study the stability of drum-shaped transition metal (TM)-doped boron clusters, M@B_<i>n</i> with <i>n</i> = 14 and 16, and M = 3d, 4d, and 5d TM atom using <i>ab initio</i> calculations. Our results show that drum-shaped M@B₁₄ clusters are favored for M = Cr, Mn, Fe, Co, and Ni, while in other cases, open conical or bowl shaped structures become more favorable. The isoelectronic Ni@B₁₄ and Co@B₁₄^– clusters have large highest occupied molecular orbital–lowest unoccupied molecular orbital gaps and these are magic clusters. Their stability has been correlated with the occurrence of magic behavior with 24 valence electrons in a disk jellium model, while for Fe@B₁₄ case the drum structure is deformed and the stability occurs at 22 delocalized valence electrons. The bonding nature in these clusters has been studied by analyzing the electron density at bond and ring critical points, the Laplacian distribution of the electron density, the electron localization function, the source function, and electron localization-delocalization indices, all of which suggest two- and three-center σ bonding within and between the two B₇ rings, respectively, and hybridization between the TM d orbitals and the π bonded molecular orbitals of the drum. The infrared and Raman spectra of these magic clusters show all real frequencies, suggesting the dynamical stability of the drum-shaped structures. There is a low frequency mode associated with the M atom. Results of the electronic spectra of the anion clusters are also presented that may help to identify these species in future experiments. Further, we discuss the stability of 24 delocalized valence electron systems Mn@B₁₆ anion, Fe@B₁₆, Co@B₁₆ cation, and other related clusters. Assembly of Co@B₁₄ clusters has been shown to stabilize a carbon nanotube-like nanotube of boron with Co atomic nanowire inside while a nanotube of boron with triangular network has been obtained with the assembly of Fe@B₁₆ drum-shaped clusters. Both the nanotubes are metallic

Proceedings of National Conference on Relevance of Engineering and Science for Environment and Society

This conference proceedings contains articles on the various research ideas of the academic community and practitioners presented at the National Conference on Relevance of Engineering and Science for Environment and Society (R{ES}2 2021). R{ES}2 2021 was organized by Shri Pandurang Pratishthan’s, Karmayogi Engineering College, Shelve, Pandharpur, India on July 25th, 2021. Conference Title: National Conference on Relevance of Engineering and Science for Environment and SocietyConference Acronym: R{ES}2 2021Conference Date: 25 July 2021Conference Location: Online (Virtual Mode)Conference Organizers: Shri Pandurang Pratishthan’s, Karmayogi Engineering College, Shelve, Pandharpur, India