Papers by Keyword: Electronic Structures

Abstract: Here, we report the bonding mechanism and electronic structure of single-walled carbon nanotube and oxygenated single-walled carbon nanotube functionalized by cellulose chain using first-principles density functional theory. Analysis of the optimized molecular configuration and charge redistribution of the nanohybrid indicates that the cellulose chain binds with the prototype single-walled carbon nanotube and oxygenated single-walled carbon nanotube via physisorption. The cellulose chain adsorption on the single-walled carbon nanotube preserved its electronic structure. On the other hand, the electronic structure of the oxygenated single-walled carbon nanotube and cellulose complex reveals that the electronic states of the cellulose tend to populate in the forbidden gap, thus, lowering the bandgap of the overall complex. The electronic structure of the complex can be considered as the superposition of its constituents in which no significant hybridization of the orbital characters is observable. The findings confirm that cellulose is indeed suitable for the non-covalent functionalization of single-walled carbon nanotubes and provide new insights into the electronic structure of the oxygenated single-walled carbon nanotube/cellulose complex.

Abstract: Organic functionalization of carbon nanotubes (CNTs) plays very important role in the development of electrochemical biosensors. In this study, pristine (5,5) carbon nanotube was functionalized by Ethanoic Acid (CH₃COOH) using First Principles Density Functional Theory (DFT). It was found that the encapsulation of CH₃COOH into the (5,5) CNT is endothermic due to the small diameter of the tube. However, interacting it outside the sidewall of the tube gives an exothermic process indicating a stable geometry. Accordingly, additional electronic bands and peaks are observed in the electronic structures of the functionalized CNT. Further, it was shown that that the p orbitals of the oxygen atoms and carbon atoms of the acid are the main contributors of the additional peaks in the valence and conduction regions, respectively. Finally, there were observed optical transitions in the functionalized CNT caused by the hybridization of the armchair CNT. Evidently, this study provided insights on more potential applications of carbon nanotubes as biosensors.

Abstract: The geometrical and electronic properties of B-doped ZnO monolayer with the concentrations of 12.5% and 25% have been calculated using the first-principles method. B-doped ZnO monolayer leads to the structural distortion around the doped atoms compared with the pure ZnO sheet. The B-B pair or two B-B pairs doped ZnO monolayer present nonmagnetic metal.

Abstract: In this paper, a first principle Density Functional Theory (DFT) method was conducted to study the geometric and electronic structures of 1-(4-chlorophenyl)-2-{[5-(4-chlorophenyl) -1,3,4-oxadiazol-2-yl] sulfanyl} ethanone, C₁₆H₁₀C_l2N₂O₂S. Using B3LYP level of theory with four basis sets of 6-31G**, 6-31++G**, 6-311G**, and 6-311++G**, the equilibrium structure of the title molecule was used to determine the total energies, Frontier molecular orbital’s energies, Mulliken atomic charges, and others. The computed findings present that four total energies obtained are close to each other, with the corresponding values of-59716.06 eV, -59709.42 eV, -59708.56 eV, and-59716.51 eV, respectively for B3LYP/6-31G**, B3LYP/6-31++G**, B3LYP/6-311G**, and B3LYP/6-311++G** methods. The calculated HOMO-LUMO energy gaps were predicted in the range of 4.001 eV - 4.089 eV. In this study, the atomic charge values of molecular system were also determined using Mulliken Population Analysis (MPA) approach. For DFT/B3LYP/6-311G** level of calculation, the computed results show that the atom of C₈ accommodates the highest negative charge in the title molecular system. All the oxygen, nitrogen, and chloride atoms are having negative charges, whereas all the hydrogen atoms are having positive charges. In addition, the dipole moment value was also determined to be 1.4758 Debye by employing DFT/B3LYP/6-311G** level of theory.

Abstract: Vacancy defects are common defects formed in the syntheses of silicon carbide nanotubes (SiCNTs) and seriously impact the electronic structures of the nanotubes. With first-principle calculations based on density functional theory (DFT), vacancy defective (6,2) SiCNTs are studied. Vacancies form a pair of fivefold and ninefold rings. Carbon vacancy introduces an occupied defect level near the top of the valence band and an unoccupied level in the conduction band. Three defect levels are found in the band gap of the SiCNT with a silicon vacancy. These results are helpful for investigations on SiCNT devices and sensors.

Abstract: The molecular structures and electronic properties of 7,8-Dichloro-4-Oxo-4H-Chromene-3-Carbaldehyde, C₁₀H₄Cl₂O₃ have been studied using Density Functional Theory (DFT) method. The calculation of geometry optimization was conducted to find the local energy minimum of C₁₀H₄Cl₂O₃ molecular system. The equilibrium geometries were used to determine the HOMO-LUMO gaps, Mulliken atomic charges, and other electronic structures of C₁₀H₄Cl₂O₃. The significant findings from DFT/B3LYP functional within the basis sets of 6-31G**, 6-31++G**, 6-311G**, and 6-311++G** show that the optimized geometries of C₁₀H₄Cl₂O₃ are in good agreement with that of measurement data. To further investigate this, using a variety of basis sets (3-21G, 6-31G, 6-31++G, 6-31G**, 6-31++G**, 6-311G, 6-311++G, 6-311G**, and 6-311++G**), it is found that the calculated total energy values of C₁₀H₄Cl₂O₃ are close to each other. Similarly, the computed HOMO-LUMO energy gaps obtained are also close to each other. Using the scheme of Mulliken Population Analysis (MPA), the trend of findings are the same for both cases of B3LYP/6-31G and B3LYP/6-31G** level of calculations. For the method of B3LYP/6-31G, it is clearly found that C₄ and C₆ have the highest positively charge, with the corresponding values about +0.284 and +0.238, respectively. On the other hand, the charge values of +0.157 and +0.206 are found on Cl₁ and Cl₂ atoms. The atoms of O₁, O₂, and O₃ have the negatively charges, with the values of about 0.398, -0.512, and -0.424, respectively. Similarly, in the case of DFT/B3LYP/6-31G** level of theory, the computed charge values of C₂ and C₄ are about +0.311 and +0.393, respectively. Furthermore, the Cl₁ and Cl₂ atoms have the positively charge values of about +0.043 and +0.070, whereas for the O₁, O₂, and O₃ atoms, the charges values obtained are about -0.421, -0.467, and -0.498, respectively.

Abstract: Antisite defects are common defects in nanotube materials and have seriously impacts on their electronic properties. Based on density-functional theory calculations, the electronic structures of the antisite defective chiral (6, 2) SiCNTs are investigated. C antisite and Si antisite lead to the formation of a depression and a bump in the surface of the nanotube, respectively. In the band gap of the SiCNT with a C antisite defect, the occupied level near the top of the valence band is formed, while the unoccupied level originating from the Si antisite defect enters the conduction band of the SiCNT.

Abstract: In this paper, we report the first principles Density Functional Theory (DFT) calculation to study the structural, energetic, and electronics properties of the 6–Bromo–4–Oxo–4H–Chromene–3–Carbaldehyde, C₁₀H₅BrO₃ molecular framework. Geometry optimization technique was carried out to find the local energy minimum of the title compound using four hybrid DFT functionals with the basis set of 6–311++G**. The optimized molecular structure of C₁₀H₅BrO₃ cluster was then used to determine the HOMO–LUMO gaps, Molecular Electrostatic Potential (MEP), Mulliken atomic charges, and others. Using the four hybrid DFT techniques, the optimized geometries of C₁₀H₅BrO₃ molecular cluster is close to that of measurement data. Our calculation results also show that the total energies obtained are close to each other with the four hybrid DFT procedures. The diagram of electrostatic potential surface show that the regions of negative electrostatic potential around the oxygen atoms, O₁ and O₂. Using the scheme of Mulliken Population Analysis (MPA), the distributions of atomic charges follow the same arguments for the B3LYP/6–311++G**, B3PW91/6–311++G**, M06/6–311++G**, and PBE1PBE/6–311++G** simulation approaches. For example, the atom of C₅ has the highest positively charge, whereas the highest negatively charge was found in the C₄ atom. For Br atom, the atomic charge values obtained are –0.158, –0.222, –0.277, and –0.224, respectively for the B3LYP/6–311++G**, B3PW91/6–311++G**, M06/6–311++G**, and PBE1PBE/6–311++G** computational methods.

Abstract: Based on first-principles calculations, we have investigated atomic and electronic structures of 4H-SiC crystal doped by N, P and As elements as n-type dopants. We have obtained the bond lengths of the optimization system, as well as the impurity levels, the band structure and the density of states. The results show that the higher impurity level above the Fermi level is observed when 4H-SiC doped by N with concentration as 6.25% in these dopants, and the band gap of 4H-SiC decreases while the doping concentration or the atomic number of dopant increases.

Abstract: The structural phase transitions and electronic structures of Co are investigated by using the first-principles calculation based on density-functional theory (DFT). Our calculated equilibrium structural parameters of Co are in good agreement with the available experimental data and other theoretical results. The calculated phase transition hcp-Co → fcc-Co at ca. 125.25 GPa. The magnetic moment of hcp-Co and fcc-Co drops to zero at 155 GPa and 77 GPa, respectively.