arXiv subjects

Ihsan Boustani

Publications and source records attributed to Ihsan Boustani.

4 recordsLinked to original sources

arXiv2025

Geometry, electronic structure, and optical properties of boron cages: A first-principles DFT study

A systematic study of the structural, electronic, and optical properties of cage-like boron clusters, with the number of constituent atoms ranging from 20 to 122, has been carried out within the framework of density-functional theory (DFT), employing 6-31G(d, p) extended basis set. The dynamic stability of the clusters is analyzed through the vibrational frequency analysis, while to study the thermodynamic stability, we computed their binding energies per atom. The results suggest that the 32- and 92-atom cages are the most stable among the small and the large structures. The optical absorption spectra of these cages is computed using the time-dependent densityfunctional theory (TDDFT), which suggests their applications in optoelectronic devices in the visible range of the spectrum.

cond-mat.mtrl-sci↗

arXiv2021

Why does B$_{12}$H$_{12}$-icosahedron need two electrons to be stable: A first-principles electron-correlated investigation of B$_{12}$H$_{n}$ ($n=$6,12) clusters

In this work, we present large-scale electron-correlated computations on various conformers of B$_{12}$H$_{12}$ and B$_{12}$H$_{6}$ clusters, to understand the reasons behind the high stability of di-anion icosahedron ($I_{h}$) and cage-like B$_{12}$H$_{6}$ geometries. Although the B$_{12}$-icosahedron is the basic building block in some structures of bulk boron, it is unstable in its free form. Furthermore, its H-passivated entity, i.e., B$_{12}$H$_{12}$ icosahedron is also unstable in free form. However, dianion B$_{12}$H$_{12}$ has been predicted to be stable as a perfect icosahedron in the free-standing form. In order to capture the correct picture for the stability of B$_{12}$H$_{12}^{-2}$ and B$_{12}$H$_{6}$ clusters, we optimized these structures by employing the coupled-cluster singles-doubles (CCSD) approach and cc-pVDZ basis set. We also performed vibrational frequency analysis of the isomers of these clusters, using the same level of theory to ensure the stability of the structures. For all the stable geometries obtained from the vibrational frequency analysis, we additionally computed their optical absorption spectra using the time-dependent density functional theory (TDDFT) approach, at the the B3LYP/6-31G{*} level of theory. Our calculated absorption spectra could be probed in future experiments on these clusters.

physics.chem-ph↗

arXiv2019

First Principles Study of Structural and Optical Properties of B$_{12}$ Isomers

In this work we undertake a comprehensive numerical study of the ground state structures and optical absorption spectra of isomers of B$_{12}$ cluster. Geometry optimization was performed at the coupled-cluster-singles-doubles (CCSD) level of theory, employing cc-pVDZ extended basis sets. Once the geometry of a given isomer was optimized, its ground state energy was calculated more accurately at the coupled-cluster-singles-doubles along with perturbative treatment of triples (CCSD(T)) level of theory, employing larger cc-pVTZ basis sets. Thus, our computed values of binding energies of various isomers are expected to be quite accurate. Our geometry optimization reveals eleven distinct isomers, along with their point group, and electronic ground state symmetries. We also performed vibrational frequency analysis on the three lowest energy isomers, and found them to be stable. Therefore, we computed the linear optical absorption spectra of these isomers of B$_{12}$, employing large-scale multi-reference singles-doubles configuration-interaction (MRSDCI) approach, and found a strong structure-property relationship. This implies that the spectral fingerprints of the geometries can be utilized for optical detection, and characterization, of various isomers of B$_{12}$. We also explored the stability of the isomer with with the structure of a perfect icosahedron, with $I_{h}$ symmetry. In bulk boron icosahedron is the basic structural unit, but, our vibrational frequency analysis reveals that it is unstable in the isolated form. We speculate that this instability could be due to Jahn-Teller distortion because five-fold degenerate HOMO orbitals in $I_{h}$ structure are unfilled.

physics.atm-clus↗

arXiv2001

Metal-Boron Nanotubes

Nanotubular materials inspired by crystalline diborides such as AlB_2 are proposed. The atomic structure, in particular the basic chemical question of where to put Al atoms in order to stabilize nanotubular Al-B systems, is investigated using density-functional calculations for prototype systems. The optimized tubular prototypes are found to be competitive in energy with their bulk crystalline counterparts. All of the tubular Al-B systems investigated are calculated to be metallic.

cond-mat.mtrl-sci↗