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DFTB Investigations on Transition Metals Doped TiO2 Quantum Dots
摘要： The structural, optical and electronic properties of different-sized pure as well as transition metals doped TiO2 quantum dots were investigated using density functional tight binding (DFTB) methods. The self-consistent charge density functional tight binding theory (SCC-DFTB) was used to model the TiO2 quantum dots (QDs) of increasing size up to 3.03 nm. The size dependence of density of states, position of molecular orbitals, and gap between highest orbital molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) of the QDs were studied. It appeared that, when the size of QDs approaches 3.03 nm, the energy gap narrowed down due to quantum confinement effects. The QD Ti27O54 was doped with 3d transition metals to further explore the possibility of tailoring the properties. The dopants introduced 3d impurity gap states which opens the opportunity to modify the band gap or positions of principal bands. The position of a shifted Fermi level was monitored to explore the changes in conductivity and n- or p-type behaviors of the doped QDs. It was observed that TiO2 QDs doped with V and Cr showed the n-type behavior while those doped with Sc, Mn and Fe showed p-type behavior. The findings are helpful to enhance the photocurrent efficiency of dye-sensitized solar cells and use the materials in electronic and optoelectronic properties.
关键词： LUMO,transition metals,DFTB,density of states,quantum dots,HOMO
更新于2025-09-23 15:19:57
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Electronic transport through defective semiconducting carbon nanotubes
摘要： We investigate the electronic transport properties of semiconducting (m, n) carbon nanotubes (CNTs) on the mesoscopic length scale with arbitrarily distributed realistic defects. The study is done by performing quantum transport calculations based on recursive Green’s function techniques and an underlying density-functional-based tight-binding model for the description of the electronic structure. Zigzag CNTs as well as chiral CNTs of different diameter are considered. Different defects are exemplarily represented by monovacancies and divacancies. We show the energy-dependent transmission and the temperature-dependent conductance as a function of the number of defects. In the limit of many defetcs, the transport is described by strong localization. Corresponding localization lengths are calculated (energy dependent and temperature dependent) and systematically compared for a large number of CNTs. It is shown, that a distinction by (m ? n)mod 3 has to be drawn in order to classify CNTs with different bandgaps. Besides this, the localization length for a given defect probability per unit cell depends linearly on the CNT diameter, but not on the CNT chirality. Finally, elastic mean free paths in the diffusive regime are computed for the limit of few defects, yielding qualitatively same statements.
关键词： defect,electronic transport,density-functional-based tight binding (DFTB),Carbon nanotube (CNT),recursive Green?s function formalism (RGF),strong localization,elastic mean free path
更新于2025-09-19 17:15:36
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[IEEE 2018 Conference on Emerging Devices and Smart Systems (ICEDSS) - Tiruchengode, India (2018.3.2-2018.3.3)] 2018 Conference on Emerging Devices and Smart Systems (ICEDSS) - Effect of Edge passivation on the Electronic Properties of Zigzag Phosphorene Nanoribbons (ZPNRs) Antidots
摘要： In this paper, we report the electronic properties of Zigzag Phosphorene Nanoribbons(ZPNRs) when passivated using different atoms. All electronic properties were calculated using the Density Functional Based Tight Binding(DFTB) Method which provide result similar to DFT method but saves computational time. Single layer PNRs structure was optimized and simulated with Hydrogen, Oxygen and without any passivation. The bandstructure, Density of States(DOS) both confirm the superiority of H passivation over others. The same calculation is repeated for the ZPNRs based antidot lattice. We observe that although ZPNRs reduce bandgap in antidot structure irrespective of the passivation, H passivated antidot lattice provide a bandgap in semiconducting range whereas other passivations return metallic behaviour.
关键词： Antidot,DFTB,ZPNRs passivation
更新于2025-09-09 09:28:46
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Simulation of Spectra of Red Fluorescent Protein Mutants
摘要： This paper presents the results of describing red fluorescent proteins using the combined quantum mechanics/molecular mechanics approach and describing the quantum-mechanical subsystem by the density functional tight-binding (DFTB) method. Based on the calculated vertical electronic transition energies, it is concluded that this method is suitable for estimating equilibrium geometry configurations, but it cannot be used for the subsequent estimation of vertical electronic transition energies.
关键词： QM/MM,DFTB,fluorescent proteins
更新于2025-09-04 15:30:14
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Spongy Nanostructures
摘要： Spongy structures are hollow-containing materials, encountered in natural or synthesized zeolites, spongy carbon, etc. The design and topological study of some hypothetical spongy nanostructures is presented in terms of map operations and genus calculation of their associated graphs, respectively. Among the discussed structures one remarks some novel spongy polyhedra that can evolve with 1-periodicity or radially, to provide multi-shell cages. Filling the space inside such complex nanostructures can be achieved by small fullerenes that self-arrange in aggregates with a well-defined geometry, of which energy trends to a minimal value. The way of space filling varies function of the dimension and shape of composing small fullerenes. An attempt of building and stability evaluating of several fullerene aggregates was made. The calculations were made at the HF, DFT and DFTB level of theory. The design of nanostructures was performed by our original software packages CVNET and Nano Studio.
关键词： HF,Fullerene,DFTB,DFT,Spongy Cage,Genus
更新于2025-09-04 15:30:14