BITS Faculty Publications
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Item First-Principal Study of the Effect of Ti Doping on Hydrogenation of Mgn (N=2-8) Nanoclusters(SSRN, 2023-02) Bandyopadhyay, DebashisWe report the effect of single Ti atom doping Mgn (n=2-8) clusters on hydrogenation kinetics using density functional theory (DFT). During growth process, variations of different energetic parameters, such as binding energy, stability, etc., with the size of the clusters, Mg4 and TiMg5, are found as thermodynamically stable. From chemisorption energies in hydrogenated Mgn and TiMgn clusters, we have estimated the catalytic effect of Ti doping in Mgn clusters to improve the dose of hydrogen. It is found that the activation barrier reduces by about 32.8% after Ti doping, as evident from the IRC study. ELF mapping indicates that the Ti doping increase the reactive sites in the Mg5 cluster, and the TiMg5 can absorb extra hydrogen molecule to attain the average binding energy of Mg5-2H. So, Ti doping in the Mg5 cluster improves the hydrogenation process as well as the dose concentration because of its catalytic activitiesItem The role of oxygen defects in the electronic, optical and phonon dispersion of the LAGO perovskite: a density functional theory investigation(RSC, 2023-10) Bandyopadhyay, DebashisThe study aims to investigate the electronic, optical and phonon dispersion properties of a pure and 2.5% O-defect induced LAGO perovskite, using density functional theory (DFT) with generalized gradient approximation (GGA) and the PBE functional. The research reveals a significant reduction in the band gap from 3.27 eV in pure LAGO to 2.18 eV in defect-induced LAGO. The defect-induced LAGO exhibits relatively strong light absorption in the visible region compared to pure LAGO. The phonon-dispersion analysis identifies one acoustic and two transverse optical mode branches. The calculated Debye temperatures for pure and defect-induced systems are 469.92 K and 463.69 K, respectively, attributed to weaker bonds in defect-induced LAGO. The findings offer fundamental insights into the impact of oxygen vacancies on the electronic, optical, and phonon properties of the LAGO perovskite that can potentially improve the electronic and optoelectronic devices operating across a wide range of spectral frequencies.Item Insights into the electronic structure and stability of TiMgn (n = 1–12) clusters: Validation of electron counting rule(Elsevier, 2022-08) Bandyopadhyay, DebashisThe present study reports the investigation of the electronic structure and stability of TiMgn (n = 1–12) nanoclusters in the framework of the linear combination of atomic orbital density functional theory (DFT) together with a spin-polarized generalized gradient approximation (GGA). We have calculated different thermodynamic and chemical parameters, such as binding energy (BE), embedding energy (EE), fragmentation energy (FE), HOMO-LUMO gap, vertical ionization potential (VIP), vertical electron affinity (VEA), etc. during the growth process of the cluster to understand their stability. From the study, the TiMg8 cluster comes out to be the most stable cluster. Further, the positive charge (Mulliken charge) on the Ti in TiMg8 cluster indicates that the Mg8-cage behaves as an electron acceptor during hybridization with the Ti. The absence of any reactive site (obtained from NBO), minimum Mg-Ti bond length, and negative NICS in TiMg8 ground state cluster support it as a globally stable cluster. Low ELF index value revealing the non-reactivity of the TiMg8 cluster. Finally, orbital analysis shows that TiMg8 clusters follow closed-cell electronic orbital sequence 1S21P61D102S2 and satisfy the 20-electron counting rule. IR and Raman spectrum calculations are also presented to understand the vibrational nature of the clusters.Item Magnetic behavior in (1≤n≤12) clusters: A density functional investigation(AIP, 2014-04) Bandyopadhyay, DebashisWith a goal to produce magnetic moment in Doped clusters which will be useful for practical applications, we have considered the structure and magnetic properties of Pure Germanium clusters and substitutionally doped it with Cr dimer to produce clusters. As the first step of calculation, geometrical optimizations of the nanoclusters have been done. These optimized geometries have been used in calculate the average binding energy per atom (BE), HOMO-LUMO gap and hence the relative stability of the clusters. These parameters have been demonstrated as structural and electronic properties of the clusters. Gap between highest occupied molecular orbital and lowest unoccupied molecular orbital indicate cluster to be a potential motif for generating magnetic cluster assembled materials. Based on these values a comparative study on different sized clusters has been done in order to understand the origin of structures, electronic and magnetic properties of nanoclusters.Item Effect of Transition Metal Doping on Hydrogenated Germanium Nanocages: A Density Functional Investigation(American Scientific Publishers, 2010-01) Bandyopadhyay, DebashisIn this report we present an ab initio electronic-structure calculations of hydrogenated germanium cages GenHnTM (TM = Cu and Zn, n = 12 to 24) using density functional theory with polarized basis set (SDD) nanoclusters. In the first step of the calculation, geometrical optimizations of the nanoclusters have been done. In the next step only the ground state optimized geometries are used to calculate the binding energy (BE), HOMO-LUMO gap and embedding energy (EE) of the clusters. Based on these values a comparative study on different doping and also with respect to the pure cages are done. It is found that though the doping with Cu can be taken favorable in the cages, but Zn is not.Item Study of electronic structure, stabilities and electron localization behavior of AgPbn (n=1–14) nanoclusters: A first principal investigation(Elsevier, 2021-07) Bandyopadhyay, DebashisPresent study reports the investigation of the electronic structure, stability and electron localization function (ELF) of endohedrally doped AgPbn clusters under frame work of density functional theory. From the variation of different thermodynamic and chemical parameters, such as, binding energy, embedding energy, fragmentation energy, chemical potential and chemical hardness, etc. during the growth process, we found that the AgPb10 and AgPb12 are relatively stable species. The density of states (DOS) explains that the strong p–d hybridization is responsible for the stability of these clusters. On the other hand, the bonding characteristics have been analyzed using electron localization function (ELF). The analysis of ELF in the most stable AgPb10 and AgPb12 clearly confirmed that the electrons are tending to localize on the outer side of the cage structure. Calculated HOMO-LUMO gaps of AgPb10 and AgPb12 clusters designate that these clusters could be useful as optical device in the visible region. Calculated IR and Raman spectrum show that the vibrational spectrum are in the far infrared region.Item Purpose-led Publishing logo. Study of pure and doped hydrogenated germanium cages: a density functional investigation(IOP, 2009-06) Bandyopadhyay, DebashisIn this paper we present an ab initio electronic-structure calculation performed using density functional theory (DFT) with a polarized basis set (SDD) within the spin polarized generalized gradient approximation for pure and divalent transition metal doped hydrogenated germanium nanocluster cages GenHnM (M = Zn, Cd and Hg, n = 6–28). In the first step of the calculation, geometrical optimizations of the nanoclusters are done. In the next step only the ground state optimized geometries are used to calculate the binding energy (Eb), HOMO–LUMO gap (ΔEg) and embedding energy of the clusters. To study the optical behaviour of the clusters, IR and Raman spectra are calculated. Further calculations on cation and anion clusters have been done only for pure and Zn doped clusters to obtain their vertical ionization potential (VIP), adiabatic electron affinity (AEA) and chemical potentialItem Electronic structure and stability of anionic AuGen (n = 1–20) clusters and assemblies: a density functional modeling(Springer, 2018-12) Bandyopadhyay, DebashisIn the present study electronic structure and stabilities of cationic gold-doped germanium clusters, AuGen (n = 1 to 20), and their assemblies have been investigated by density functional theory (DFT) modeling. Computational results show a good relationship between the thermodynamic parameters, average binding energy, embedding energy, fragmentation energy, etc., with the percentage hybridization between different Ge 4s, Ge 4p, and Au 5d atomic orbitals, which plays a dominating role in the stabilization of anionic AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Other thermodynamic and chemical parameters are also found consistent with the observed thermodynamic stabilities of the nanoclusters. In smaller size range (n < 11), Au atom always absorbs on the surface or vertex of pure Ge cluster. From n = 11, endohedral doping starts. In the assembled clusters, Au atom play the role as a bridging atom in Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Stability of the AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 are explained using magic number in shell-filled model and mixed (π-σ) aromatic rule. As per the symmetry and structure of AuGe12 cluster, it is comparable to a nido-cluster, and hence, its stability is explained using Wade-Mingos rule. Calculated VDE, ADE, HOMO-LUMO gap, and VIP have very close agreement with the experimental results. IR and Raman frequencies show that the vibration nature of the clusters could produce electromagnetic radiation in the far infrared region which is useful for medical applications.Item Chemisorptions effect of oxygen on the geometries, electronic and magnetic properties of small size Nin (n = 1-6) clusters(Springer, 2011-05) Bandyopadhyay, DebashisThe present study reports the effect of oxygen addition on small size Nin (n = 1-6) clusters in different spin states within the framework of linear combination of atomic orbital (LCAO) density functional theory (DFT) under spin polarized generalized gradient approximation (GGA) functional. Relative stabilities of the optimized clusters are discussed on the basis of the calculated parameters, such as, binding energy (BE), embedding energy (EE) and fragmentation energy (FE). Other parameters, like ionization potential (IP), electron affinity (EA), etc. show that though the additions of oxygen can affect the chemical properties of Nin clusters with an additional stability to NinO. In most of the cases the magnetic moment of the stable isomers are geometry dependent for a particular size both in pure and oxidized clusters. Calculated magnetic moments of NinO (n = 1-6) clusters reveal that the magnetic moment of ground state Ni4O isomers in different geometries is same as in pure Ni4 isomers. Present study also explains the cause of stable magnetic moment in Ni4O cluster through the distribution of electrons in different orbitals.Item Study of the electronic structure, stability and magnetic quenching of CrGen (n = 1–17) clusters: a density functional investigation(RSC, 2015-09) Bandyopadhyay, DebashisIn the present report the evolution of the electronic structure, stability and magnetic quenching of CrGen nanoclusters has been carried out using density functional theory (DFT). From the nature of the variation of the different thermodynamic and chemical parameters, the CrGe10 and CrGe14 ground state clusters are identified as the most stable species. It is observed that the enhanced stability of CrGe10 and CrGe14 are due to the closed shell filled structure of the Cr-atomic orbitals and follow the 18-electron counting rule. It is found that the strong mixing of the Cr d-orbital with the s- and p-atomic orbitals of the Ge atoms in the cluster are mainly responsible for the stability and quenching of the Cr magnetic moment in the clusters. Calculated CPs also give additional information about the bonding and its effect on the stability of the clusters. Calculated IR and Raman spectra also support these results.