The planar B 6 cluster as a motif for doping metal cation (Al 3+ ): A DFT study Md. Rakib Hossain 1 , Milon 2 , Syed Mahedi Hasan 3 , Md. Kamal Hossain 4 , Jahirul Islam Khandaker 5 , Farid Ahmed 6 , Md. Abul Hossain 7 Department of Physics, Jahangirnagar University, Savar, Dhaka-1342 Email: rakibju.r@gmail.com 1 , milonpaul8@gmail.com 2 , tamim840@gmail.com 3 , khossain@juniv.edu 4 , kijahir80@juniv.edu 5 , fahmed@juniv.edu 6 , mdabulh@juniv.edu 7 Abstract— This present research investigation reports various properties of doped and undoped boron cluster (B 6 ) such as charge distribution, stability, adsorption energy, dipole moment, reactivity, vibrational frequency, optical property, orbital analysis etc. on the basis of B 6 motif, which is actually the hexagonal vacancy of borophene (B 36 ) cluster. We have used the density functional theory (DFT) calculations at the B3LYP/SDD level of theory. At first, we have studied the properties of B 6 motif and then Al-doped B 6 cluster with pyramidal and bi-pyramidal geometries have been investigated and compared them with the planar B 6 motif. Keywords— DFT; B3LYP/SDD; Motif; 2D Material; Borophene; UV-Visible Spectrum; IR Spectrum; HOMO-LUMO Orbital I. INTRODUCTION Graphene, an allotrope of carbon, is a single layer of bulk graphite which was first synthesized by Novoselov, Geim and co-workers in 2004 [1]. After their ground breaking work, scientific community started to work enormously to enhance its properties and graphene now has many important commercial applications. Graphene shows very good physical, chemical and mechanical properties which make it more attractive. It can be used as electrode for various cells and batteries [2], sensors [3], in numerous bio-medical applications [4], as light harvester [5] and in other promising applications [6]. After the successful investigation on various graphene based devices, researcher started to study and conceivably synthesize more two dimensional nanosheet based on other elements from their three dimensional structure or utilizing a bottom-up synthesis route. Graphyne, Borophene, Germanene, Silicene, Stanene, Phosphorene, Molybdenite are some notable examples that has been previously synthesized and similar to a two dimensional layer of carbon they consists of boron, germanium, silicon, tin, phosphorus, molybdenum respectively. These nanosheets also exhibit very promising phenomena similar to graphene. Pure boron is an electron deficient element which forms cage like fullerene structure and an excellent candidate for 2D nanosheet, the so called “borophene”. The 2D layer of boron has various chemical structures which forms by changing the number of boron atoms and by adding other atoms on the system and possesses diverse bonding characteristics. The first synthesis and characterization of planar boron is a triple-decker complex containing a planar, six-membered 1,2-B 6 H 4 Cl 2 ring which attracted the scientific community as an potential 2D nanosheet [7]. In recent years, researchers put a lot of effort to theoretically investigate this nanomaterial and also experimentally synthesize several boron clusters with different coordination number. Recently, scientists has successfully synthesized various boron planar and quasiplanar boron clusters with/out doping other elements of periodic table [8]. In case of large number of boron atoms in the cluster, tetragonal, pentagonal, hexagonal vacancies are created for the combined charge distribution of the boron atoms. Tetragonal and pentagonal vacancies are created for up to B 23 cluster [9] and hexagonal vacancy is created for B 36 cluster and it is observed that various change of electrical and chemical properties are occurred for the modification of the hexagonal vacancy of B 36 cluster [10]. In our investigation, we have studied hexagonal B 6 motif to understand the nature of boron cluster containing such hexagonal vacancy by performing different calculation. We have also investigated the B 6 motif by incorporating metal (Al) atom and studied the change of various properties of the doped boron cluster. We have calculated the adsorption energy and other related parameters for understanding the stability of adsorbed structures. The global minimum searches have been carried out from the HOMO-LUMO energies. We have visualized the HOMO-LUMO energy gaps by density of state (DOS) spectrum. The HOMO-LUMO energy gaps, chemical potentials, charge transfer abilities have been also investigated. The optical property has been studied from the ultra violet visible spectra calculation. II. COMPUTATIONAL METHOD All quantum mechanical calculations have been executed by Gaussian 09 program [11]. The geometry of B 6 motif and the structures with added atom have fully been optimized by density functional theory (DFT) employing Becke’s (B3) [12] exchange functional combining Lee, Yang, and Parr’s (LYP) correlation functional [13] which is known as B3LYP level of theory and we have used SDD basis set [14] because our investigating system is in gas phase. After completing the initial geometry, molecular orbital calculations have been performed at the same level of theory. The adsorption energies 978-1-5386-3341-0/17/$31.00 ©2017 IEEE