Abstract: Transition metals (TM) have reasonable possibility to involve in nanoclusters and capability of changing apparent properties of cluster materials. Doping is a popular technique for modifying band gap to enhance electrical properties along with others by introducing impurities to a pure structure. We’ve focused on computational DFT study on the hexagonal vacancy of B36 cluster (B6 nanocluster), centered at middle on B36 cluster. Since TM doped boron structures have not been studied quite well, we have investigated B6 cluster by doping Mn atom both in pyramidal and bi-pyramidal fashion. B3LYP hybrid functional and two different basis sets (SDD and LanL2DZ) have been used for the comparative study of pristine and doped B6 cluster. We’ve investigated various structural, electronic, optical, chemical and adsorption properties of pristine and doped B6 cluster. From our theoretical investigation, we’ve found that doped structures are more stable than pristine nanocluster and more prone to absorb broader electromagnetic radiation.
Keywords: Density functional theory; transition metal; pyramidal and bi-pyramidal structures; bandgap; adsorption
Being highly catalytic and having the capability of contributing to delocalized bonds, TMs have been chosen to be more suitable candidate to occupy the center of wheel like Bn clusters 1 and B6 cluster has theorized and experimentally shown by Piazza et al. 2. Graphene, an allotrope of carbon, first isolated and characterized by A. Geim and K. Novoselov in 2004, has been in peak interest for a considerable amount of time for its superior properties i.e. ultrahigh carrier mobility, thermo-electric conduction and many others 3. For the potential applications of 2D materials such as graphene, along with germanene, graphyne, stanene, phosphorene and silicene, immense interest has grown for searching other 2D materials and finding their properties. Like graphene, the two-dimensional nanocluster of boron (nearest neighbor to carbon), called borophene is both predicted and synthesized in past few years 2,4. Though being an electron deficient element in nature, boron cannot form graphene-like honeycomb structures, researchers anticipated borophene to be another promising 2D material with outstanding characteristics 2.
Nanoclusters of boron are being investigated since last century. X. Yang et al. investigated the electronic and structural properties of a novel boron flat metal sheet and the relative boron nanotubes and observed that larger boron nanotubes are metals and behave as semiconductors with the gap decreasing as the chiral angle and radius increase 4. In the investigations of Ruan Wen et al. they found that Na atom(s) decorated various B6 nanocluster complex show that it is viable for hydrogen storage application in ambient conditions 5. The results from the study of structures of bare and oxidized boron nanoclusters from Michael L. Drummond et al. provided a fundamental basis for developing an understanding of boron oxidation at molecular level. They proposed that small boron and oxidized boron nanoclusters can act as artificial fuel based on highly exothermic and versatile oxidation of boron 6. Photoelectron spectra were obtained for B_7^- at several photon energies from investigations of Alexander I. Boldyrev et al. who investigated electronic structure and chemical bonding of B_7^- and B7 using photoelectron spectroscopy and ab initio calculations. From their analyses of the molecular orbitals and chemical bonding it is evident that the triplet pyramidal structure has twofold aromaticity, the singlet pyramidal structure shows both aromaticity and antiaromaticity, and the singlet planar structure shows a twofold antiaromaticity 7. Alexandrova et al. also explored the structural and electronic properties and chemical bonding in anion B_6^- and B6 using photoelectron spectroscopy and ab initio calculations. They observed that B_6^- structure to be planar and antiaromaticity was present in the odd-electron system 8. Whereas, Ravindra Shinde and Alok Shukla investigated linear optical absorption spectra in neutral boron nanocluster B6 and cationic B_6^+ using first principles correlated electron approach. They found the nature of optical excitation were collective and plasmonic 9. Bo Peng et al. investigated bonding properties and electronic structure of borophene by first-principle calculations and they observed both high optical transparency and electrical conductivity in borophene, which makes it an ideal candidate for transparent conductors 10. The metallicity and densities of states (DOS) around fermi energies indicate that borophene might exhibit Dirac transport characteristics and phonon-mediated superconductivity 11–14. The finding from T. Jian et al. suggests that another type of metal-stabilized tubular boron nanoclusters can provide with a new bonding modality for transition metals (TM) and a new concept for designing boron-based nanomaterials 15.
From concurrent computational studies, it is found that a triangular planar boron lattice with hexagonal vacancies in the middle is more stable which would be very suitable to form the putative boron nanotubes and these hexagonal vacancies are possibly a key to the stability of the proposed B80 fullerene 4,16,17. We are interested in this hexagonal pristine and TM (manganese-Mn) doped boron nanocluster and its properties upon modification. We have investigated the stability of these structures from adsorption energy and IR spectra analysis. Thermodynamic parameters such as enthalpy, Gibbs free energy and entropy have been studied for the better understand of the adsorption behavior of the nanoclusters. We’ve studied electrical property of pristine and doped B6 nanocluster from Mulliken charge distribution and dipole moment. From the DOS plots and electron densities in highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) molecular orbital (MO) analyses have been performed. By investigating the circular dichroism (CD) and ultra-violet visible (UV-vis) spectra analysis, we’ve studied the possible interaction of pristine and doped structures with electromagnetic radiation. Global parameters i.e. chemical potential (µ), hardness (?), softness (S) and electrophilicity (?) of pristine and doped structures were calculated from HOMO, LUMO energies to understand reactivity of relative structures.