Replacing Carbon Atoms Research Articles

A DFT study on the fundamental mechanisms of quantum capacitance enhancement within the carbon-based electrodes through different classes of doped configurations from biomass-derived elements

Density functional calculations were performed on 15 functionalized graphene models to investigate the enhancement of quantum capacitance (CQ) by common dopant elements N, P, S, and O from biomaterials. Geometry optimizations and formation energy calculations demonstrated that the van der Waals radius and additional covalent bonds influenced the mechanical stress and formation energy, particularly due to the distortion of the graphene lattice caused by larger S or P atoms replacing carbon atoms. According to both the CQ and formation energy calculations, nitrogen emerged as the most promising doping element for enhancing CQ, followed by phosphorus, while sulfur showed a relatively lower contribution. Electron density profiles indicated that the improvement of CQ was facilitated by the lone pair electrons at the defects. The effects of dopants on electronic structures were further elucidated through CQ characteristics, resulting in the classification of functionalized graphene models into three types. The ‘graphitic’ type represented configurations that preserved most of the electronic structure of pristine graphene, while ‘p-type’ and ‘n-type’ represented those experienced the loss and gain of valence electrons, respectively. This electronic structure-based classification of doping provides valuable insights for future designs, enabling control over sintering and doping conditions in biomass-derived electrode materials for supercapacitors.

Quantum interference and spin transport in M-OPE molecular devices controlled by N or B atom substitution

In this paper, the first-principles method based on density functional theory and non-equilibrium Green’s function is used to investigate the modulation of quantum interference and spin transport in N and B atom substituted meta-phenylene (M-OPE) molecular devices. The zero bias spin transmission spectrum of M-OPE molecular device shows that highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are located at higher energy positions on both sides of the Fermi level, and there is a clear transmission spectrum valley (anti resonance peak) on the right side of the Fermi level. This indicates that M-OPE molecules are typical destructive quantum interference molecular systems. Research has found that N and B atoms replace carbon atoms at positions 1, 2, and 3 on the central ring of the molecule, which suppress the original destructive quantum interference of M-OPE molecular device to different extents. The substitution of N and B atoms at position 1 has no effect on the original destructive quantum interference of M-OPE molecular device, while the substitution of N and B atoms at positions 2 and 3 significantly suppresses the original destructive quantum interference of M-OPE molecular device. Therefore, there is a significant difference in the electrical conductivity of devices with N and B atoms at different positions, with the order of electrical conductivity values being N2 > N3 > N1 and B2 > B3 > B1. In this study, it is also found that the spin current value of device with B atom substitution is significantly higher than that of device with N atom substitution. After the substitution of B atom at position 2, the spin current value of the device under negative bias is significantly greater than that under positive bias, exhibiting a significant spin rectification effect. Based on the extended curled arrow rule proposed by O’Driscoll et al. to predict the behavior of quantum interference effects, we explain the physical mechanism by which N and B protons at different positions have different effects on the suppression of quantum interference in M-OPE molecular device. The results of the quantum interference and spin transport regulation of molecular systems by the substitution of B and N atoms can provide theoretical guidance for realizing the further application of heterocyclic aromatic hydrocarbons in molecular electronics.

Investigating the thermoelectric properties of the (6, 6) two sided-closed single-walled boron nitride nanotubes ((6, 6) TSC-SWBNNTs) due to the impurity of a single carbon atom and temperature changes

In this research, the thermoelectric properties of the (6, 6) two sided-closed single-walled boron nitride nanotube ((6, 6) TSC-SWBNNT) was investigated in the state without impurity and carbon atom impurity instead of boron and nitrogen atoms in the center, left, and right the nanotube. The test conditions were the energy range of −5.5 to 5.5 eV and temperatures of 200, 300, 500, 700, 900, 1100, and 1300 K. Based on the obtained results, with an increase in temperature and the creation of impurities, the band gap is affected and becomes noticeably smaller. At the temperature of 1300 K, the band gap shows the greatest decrease and the peak height shows the least decrease. With increasing temperature, the number of peaks has decreased, suggesting an increase in the mobility of electrons and holes and a decrease in their localization. The Seebeck coefficient figures also changed by replacing carbon atoms with boron and nitrogen atoms in different parts of the nanotube. In addition, the height of the heat conduction peaks increased with increasing temperature. However, the heat conduction values are generally in the range of 9–10 nm, which are small values. With the increase in temperature, ZT values increased such that the highest values corresponded to the temperature of 1300 K. The ZT values higher than 1, especially at high temperatures, show that (6, 6) TSC-SWBNNT nanotubes are suitable candidates for thermoelectric materials.

In English

The hexagon-shape graphene nanoflakes (GNFs) limited by zigzag edges only (with doubly and triply coordinated atoms) have unique increased reactivity. Despite the high systems symmetry (D6h) the Carbon atoms in GNFs occupy non-equivalent positions. Can such physical and chemical characteristics of GNFs, which depend of the atom position in the cluster, definition? This characteristic together with the simplicity of its calculation makes it possible to predict the properties of nanoflakes obtained from GNFs by introducing single and multiatomic vacancies into them or by replacing Carbon atoms with electron withdrawing and electron donating atoms. This characteristic includes the C1s core-level binding energy shifts, the maxima of which characterize the C atoms of a certain type. The proposed work is devoted to quantum chemical calculations of the electronic density of states (DOS) of pristine hexagon-shape GNF C96 (multiplicity, M=5), their saturated counterpart –polycyclic aromatic hydrocarbon(PAH) C96H24 (M=1) and their derivatives with one and two single vacancies in the ground electronic state (GES). All calculations were performed using the density functional theory (DFT) method with the involvement of the valence-split basis set 6-31G (d,p). Systems with open shells were considered using the UB3LYP exchange-correlation functional. The obtained spectra were fitted using Gaussian curve fitting program to determine the binding energy for each peak. The Gaussian function distribution of the theoretically calculated C1s core-level binding energy shifts of GNFs testified the presence of six peaks, each of which refers to a certain type of Carbon atoms. The C1s peak with the highest binding energy (-285.57 eV) is caused by contributions from the doubly coordinated edge cyclic chain (ECC) Carbon atoms. The C1s orbitals of the central hexagon (CHex) atoms and the first cyclic chain (FCC) atoms form delocalized molecular orbitals (MOs) in different parts of the cluster. The analogous spectrum of PAH C96H24 is slightly shifted to the region of lower binding energies and contains only two well-defined peaks. The peak with a higher binding energy (-284.36 eV) is generated by the 1s states of the CHex atoms and the atoms of the FCC, which are bounded to the CHex atoms. The electronic DOS difference in C1s core-level spectra of GNF C96 (M=5) and their saturated counterpart PAH C96H24 is established due to the presence of two weakly bounded π-systems in GNF and common conjugated system in PAH. The electronic DOS of defect-containing cluster C96-1(1) (M=3) (one CHex atom has been removed from the C96nanoflake) is generated by the C1s core-level atoms of the second cyclic chain (SCC), which are located at the different distances from the center of the nanoflake. The peak of the lowest intensity (-284.63 eV) appears in the spectrum as a reflection of the appearance of doubly coordinated Carbon atoms surrounding the single vacancy in the C96-1(1) nanoflake. The analysis of the electronic DOS of the C1s core-level spectrum of the C96-2(1) nanoflakeis shown, that doubly coordinated Carbon atoms, concentrated around two single vacancies, are essentially non-equivalent. If the MO with the lowest binding energy is localized on two of them – the MO with the highest binding energy is localized on the third atoms (one around each single vacancy). The electronic C1s core-level DOS spectrum of defect-containing molecular systems with one C96-1(1)H24 and two C96‑2(1)H24 single vacancies are similar to the analogous spectrum of PAH C96H24. In the first of them – one additional maximum appears due to C1s atoms surrounding the single vacancy. In the second – there are two additional maxima, each of which is generated by C1s core-level atoms adjacent to individual vacancies.

New diamond-like phases boron nitride TA-type

A theoretical study of the structure and electronic properties of three new polymorphic varieties of diamond-like phases of boron nitride, the atoms of which are in equivalent crystallographic positions, was carried out by the density functional theory (DFT) method in the generalized gradient approximation (GGA). The primary structures of these phases were built modelically from the corresponding carbon diamond-like phases by replacing carbon atoms with alternating boron and nitrogen atoms, so that an atom of one kind was surrounded by atoms of another kind. As a result of the calculations, the possibility of stable existence of new structural varieties of boron nitride was established: BN-TA1, BN-TA2, BN-TA3. The sublimation energy of new BN phases varies from 17.08 to 17.59 eV(BN)−1. The new BN polymorphs are wide-gap semiconductors with a band gap at the Fermi energy level from 3.6925 to 5.4565 eV.

Important But Overlooked Potential Risks of Substituted Polycyclic Aromatic Hydrocarbon: Looking Below the Tip of the Iceberg

Substituted polycyclic aromatic hydrocarbons (PAHs) are PAH derivatives in which substituents replace hydrogen atoms on the aromatic benzene ring, or N/S/O atoms replace carbon atoms in aromatic rings. Compared to unsubstituted PAHs, some substituted PAHs have higher pollution levels and more significant toxicity than their parent PAHs (p-PAHs), and the International Agency for Research on Cancer (IARC) lists them as possible human carcinogens, which harm human health but lack sufficient examination. This paper summarizes and discusses the environmental occurrence and distribution, toxicity, and impacts of substituted PAHs on human health and compares with the 16 representative priority-controlled PAHs (PAHs16). According to occurrence of PAHs in various environmental media, it is shown that the mean concentration of individual substituted PAH in the air is higher than that of individual PAH16. The mean concentration of individual substituted PAH in the soil varies widely among different countries, with a difference of 100,000 times between the lowest level (Italy) and the highest level (USA). The mean individual alkylated PAH (APAHs) and oxygenated PAH (OPAHs) are the most abundant in surface water and sediments. In the aspect of toxicity effects, some substituted PAHs have been proved to have similar or identical toxicity as PAHs16. We summarize existing problems and propose future priority research areas through the analysis of the occurrence and toxicity of substituted PAHs in the environment, which is important for further research and regulation of substituted PAHs.Graphical Abstract

Six novel silicon carbide with direct bandgaps: A comprehensive study

Six new SiC phases with direct bandgaps were found by replacing carbon atoms with carbon and silicon atoms with a stoichiometric ratio of 1:1 in the SACADA-Samara Carbon Allotrope Database of 522 pure carbon structures via the global search method. The six newly discovered SiC phases are in the space groups of Pccn, P4/ncc, Pmn21, P63/m, I4¯3m, and Pnma, in which crystal structures, stabilities, elastic anisotropy, electronic and effective mass were investigated in detail based on first-principles calculations. The formation energies of Pmn21-SiC and Pnma-SiC are very close to that of F4¯3m-SiC, revealing their superiority in experimental implementation. Pccn-SiC, P4/ncc-SiC, Pmn21-SiC, and Pnma-SiC have better compression resistance than F4¯3m-SiC. All the proposed structures are direct bandgap semiconductors with a wide bandgap range of 2.86 ∼ 3.72 eV, which have a smaller effective mass than diamond silicon, giving promising applications in high-frequency, high-temperature and high-power electronic devices.

Gourava descriptors of multi‐dimensional flat and stable tri‐hexagonal boron nanotubes

AbstractGourava indices of boron nanotubes (BNT) are used to study the physical and electronic properties of nano semiconductor devices. Gourava indices have an important role in the study of high thermal conductivity and nano‐scale mechanical properties of semiconductors. These indices are also used to study the applicability of BNTs in the field of energy storage, and biomedical medicines. Since BNT like carbon nanotubes have almost the same tubular structure obtained by replacing carbon atoms with boron atoms. Therefore, they require theoretical study to establish structural changes in BNTs. In this paper, we compute the first and second Gourava descriptors, first and second hyper Gourava descriptors, sum and product connectivity Gourava descriptors and general first and second Gourava descriptors for the tri‐hexagonal BNTs.

Methane adsorption on the surface of metal (Fe, Ni, Pd) decorated SWCNT: A density functional theory (DFT) study

Adsorption of methane gas on the catalytic systems comprising (8, 0) single walled carbon nanotube (SWCNT) decorated with transition metals (Fe, Ni, Pd) were investigated using plane-wave density functional theory. SWCNT was modified by adding these transition metals to both inside and outside the nanotube and replacing carbon atoms with them. All structures were relaxed and their structural and electronic properties were investigated before and after CH4 adsorption. The obtained results indicate that metal modified nanotubes exhibit good sensitivity and selectivity to methane. Adsorption energy results show that modifying nanotubes with Ni on the surface are more effective at adsorbing CH4 as compared to systems containing Fe and Pd atoms on the surfaces. CH4 adsorption on the surface of CNT decorated with transition metals changed both electronic and magnetic properties which show that these nanotubes are good candidate for detecting methane from the environment.

H2S adsorption on pristine and metal-decorated (8, 0) SWCNT: a first principle study.

Adsorption of hydrogen sulfide (H2S) on the surface of catalytic systems containing (8, 0) single-walled carbon nanotube decorated with Ni and Pd transition metals was investigated using plane-wave density functional theory. SWCNT was modified by adding Ni and Pd atoms to both inside and outside the nanotube and replacing carbon atoms with these metals. All structures were relaxed, and their structural and electronic properties were investigated before and after H2S adsorption and compared with pristine (8, 0) SWCNT properties. Obtained results showed that decorating CNTs with metals increases CNT efficiency for H2S adsorption. The most negative adsorption energies were observed when H2S was adsorbed on the surfaces of metal-decorated nanotube. Electronic properties like band structures and density of states indicated that systems containing Ni on SWCNT are more effective at adsorbing and sensing H2S molecules. Hydrogen sulfide adsorption also changed the magnetization of Ni-decorated structures. Moreover, adsorption of H2S from H side to Ni-decorated SWCNT leads to dissociation of H2S to HS and S atom. Obtained results showed that metal-decorated nanotubes are potentially good candidates for separating H2S from industrial waste gas streams and for its use in H2S sensors.

Effects of carbon nanomaterials on the migration and fate of organic pollutants in the ecological environment

The purpose of this study was to investigate the mechanism of adsorption reaction between heterocyclic organic compounds with different number of ring atoms and different atoms replacing carbon atoms and carbon nanotubes with different surface functional groups. Based on the current situation of research on adsorption of carbon nanomaterials adsorbing organic pollutants, the existing problems and limitations were analyzed by studying the properties and characterization of single-walled carbon nanotubes, oxidized single-walled carbon nanotubes and non-porous graphite powder, such as elemental analysis, transmission electron micrograph, zero charge point, etc. The three adsorption materials were investigated by batch experiment. Six compounds of thiophene, pyrimidine, benzene, aniline, 2-aminopyrimidine and 4,6-diaminopyrimidine were selected as the adsorbate for detecting adsorption capacity. The results showed that the affinity of different adsorbents on different adsorbents varied greatly. The adsorption capacity of heterocyclic compounds containing N and S was greatly enhanced by non-hydrophobic action. And the degree of oxidation of the adsorbent and the ph of the solution determined the adsorption capacity of the adsorbent for nitrogen-containing heterocyclic compounds. Therefore, in the ecological environment, the migration of hydrophilic organic pollutants in the environment can be reduced by the preparation of appropriate carbon nanotubes.

BN adamantane isomers: an optical absorption spectrum study

In this work, we have systematically investigated the structural, electronic, and optical absorption properties of the boron nitride (BN) adamantane isomers (B $$_x$$ N $$_{10-x}$$ , with x= 4, 5 or 6), using both DFT and TD-DFT methods. These isomers were built by replacing carbon atoms of the adamantane molecule by boron and nitrogen atoms and keeping all isomers in closed-shell electronic configuration. Optimized nanostructures indicate that these BN adamantane exhibit good stability. In addition, the current study indicates that the new BN-isomers have an excellent absorption in the UV-C region, and a moderate absorption in the UV-B and UV-A regions. These characteristics enable this new BN adamantane as potential candidates to be used in the development of new nano-optoelectronic devices.

En Route Towards the Control of Luminescent, Optically-Active 3D Architectures.

π‐Extended systems are key components for the development of future organic electronic technologies. While conceiving molecules with improved properties is fundamental for the evolution of materials science, keeping control over the 3D arrangement of molecules represents an ever‐expanding challenge. Herein, a synthetic protocol to replace carbon atoms of π‐systems by dissymmetric phosphorus atoms is reported; in particular, it allowed for conceiving new fused phosphapyrene derivatives with improved properties. The presence of dissymmetric phosphorus atoms precluded the formation of excimers. X‐ray diffraction revealed that, meanwhile, strong intermolecular interactions are taking place in the solid state. The phosphapyrenes photoluminesce in the visible region with high quantum yields; importantly, they are CD‐active. In addition, the unique non‐planar features of phosphorus atoms allowed for the control of the 3D arrangement of molecules, rendering lemniscate‐like structures. Based on our discoveries, we envisage the possibility to construct higher‐order, chiral 3D architectures from larger phosphorus‐containing π‐systems.

Density functional theory studies of effects of boron replacement on the structure and property of RDX and HMX

AbstractIn this study, based on two model nitramine compounds hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) and octahydro‐1,3,5,7‐tetranitro‐1,3,5, 7‐tetrazocine (HMX), two series of new energetic molecules were designed by replacing carbon atoms in the ring with different amounts of boron atoms, their structures and performances were investigated theoretically by the density functional theory method. The results showed that the boron replacement could affect the molecular shape and electronic structure of RDX and HMX greatly, and then would do harm to the main performance like the heat of formation, density, and sensitivity. However, the compound RDX‐B2 is an exception; it was formed by replacing two boron atoms into the system of RDX and has the symmetric boat‐like structure. Its oxygen balance (4.9%), density (1.91 g/cm3), detonation velocity (8.85 km/s), and detonation pressure (36.9 GPa) are all higher than RDX. Furthermore, RDX‐B2 has shorter and stronger NNO2 bonds than RDX, making it possesses lower sensitivity (45 cm) and better thermal stability (the bond dissociation energy for the NNO2 bond is 204.7 kJ/mol) than RDX. Besides, RDX‐B1 and HMX‐B4 also have good overall performance; these three new molecules may be regarded as a new potential candidate for high energy density compounds.

Enhanced oxygen-induced properties of bulk oxygenated amorphous carbon films deposited with an anode layer ion source

Bulk oxygenated amorphous carbon films (a-C:H:O) with different oxygen concentrations are deposited on high-speed steel with a chromium carbide (CrCx) interlayer using an anode layer ion source (ALIS) and their structural, mechanical, and tribological properties are determined. Films with 7 at%, 9 at%, 13 at%, and 27 at % oxygen are prepared by changing the O2 to C2H2 ratio in the gas mixture during deposition. The film deposited without intentionally introducing oxygen has an oxygen concentration of 5% and serves as the control sample. The surface of the control film contains nanodots which can be reduced with 10% O2 in the gas mixture. The best properties are obtained from the film containing 7 at% oxygen. The hardness increases from 19.5 GPa for the control film to 29.0 GPa of the a-C:H:O film with 7 at% oxygen. At the same time, the wear rate decreases by 2.5 times to 2.0 × 10−7 mm3/m-N and the friction coefficient by 10 times to 0.09. If the oxygen concentration in the film exceeds 7%, the hardness begins to decrease and wear rate increases while the friction coefficient is reduced slightly. Raman scattering reveals a smaller ID/IG ratio and more disorder in the 7% sample and XPS shows that the improvement stems from increased sp3 hybridization and C–C bonding. However, if the oxygen concentration in the gas mixture is increased further, oxygen ions begin to replace carbon atoms in the sp3 structure and more O–C–O, CO, and O–CO bonds are created. The carbonyl and carboxylic groups soften the matrix and degrade the mechanical properties. Our results clarify the effects and mechanism of oxygen on the mechanical and tribological properties of bulk amorphous carbon films.

Abstract 3: Discovery and optimization of small molecule Bax activators for cancer therapy

Abstract Bax, an indispensable executioner protein of B-cell lymphoma 2 (Bcl-2) family, plays a pivotal role in controlling the mitochondrial dysfunction and apoptosis in normal and cancer cells. High throughput screening to combat the nicotine-induced Bax phosphorylation at serine 184 (S184) to activate the proapoptotic function of Bax has revealed compound SMBA1 as a promising Bax direct activator as we previously reported. Initial medicinal chemistry campaign by choosing SMBA1 as a lead compound for breast cancer treatment resulted in the identification of compound CYD-2-11 with low micromolar IC50 values against MDA-MB-231 and MCF-7 as well as in vivo inhibitory effects against MDA-MB-231 xenograft tumor growth. Herein, we report the comprehensive structural optimization based on CYD-2-11 as the lead by introducing various alkylamino side chains to have a deeper access to S184 pocket and replacing carbon atoms with nitrogen as well as reducing the nitro group of 9H-fluorene scaffold to construct diverse derivatives for enhanced drug properties. CYD-4-61 and GL0385 have been discovered as the most potent anti-breast cancer agents with submicromolar IC50 values of 0.34 and 0.33 µM against MDA-MB-231 as well as 0.65 and 0.26 µM against MCF-7, respectively. More importantly, these drug candidates exhibited significant in vivo efficacy suppressing xenograft tumor growth by activating Bax to induce cancer cell apoptosis with the potential to overcome resistance against Adriamycin (ADR) in breast cancer. This work was supported by Breast Cancer Research Program (BCRP) Breakthrough Award BC160038 (to J.Z.) and BC160038P1 (to Q.S.) from the Department of Defense (DoD). Citation Format: Gang Liu, Hyejin Kim, Chunyong Ding, Zhuo Yu, Hong Wang, Haiying Chen, Qiang Shen, Jia Zhou. Discovery and optimization of small molecule Bax activators for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3.

DFT study on electronic and optical properties of graphene modified by phosphorus

The photoelectric properties of graphene are modulated by replacing carbon atoms with phosphorus atoms. The studies have revealed that the band gap of graphene is opened after adding phosphorus atoms and the Dirac cone disappears. The Fermi level goes into the conduction band, which behavior is similar to n-type doping. The band gaps of phosphorus-doped graphene are 0.166 eV, 0.32 eV, 0.811 eV, 0.86 eV and 1.262 eV, respectively, and the corresponding phosphorus doping concentration are 3.125%, 6.25%, 9.375%, 12.5% and 15.625% successively. For phosphorus-doped graphene, phosphorus atom gains electrons while carbon atom loses electrons. The loss of electrons for carbon atoms mainly come from C-p orbitals, a few contributions come from C-s orbitals. The effective widths of the absorption spectra of the phosphorus-doped graphene are narrower than that of the pristine graphene, and the peak value is reduced, too. Interestingly, when the doping concentration is lower than 9.375%, the reflectivity of pristine graphene is higher than that of phosphorus-doped graphene. When the concentration of phosphorus are 9.375%, 12.5% and 15.625%, electrons are prone to inelastic collisions with incident electrons. The results of the study provide a theoretical basis for the future application of graphene in optical and optoelectronic devices.

Structure-activity relationship studies on Bax activator SMBA1 for the treatment of ER-positive and triple-negative breast cancer

In an effort to develop novel Bax activators for breast cancer treatment, a series of diverse analogues have been designed and synthesized based on lead compound SMBA1 through several strategies, including introducing various alkylamino side chains to have a deeper access to S184 pocket, replacing carbon atoms with nitrogen, and reducing the nitro group of 9H-fluorene scaffold. Compounds 14 (CYD-2-11) and 49 (CYD-4-61) have been identified to exhibit significantly improved antiproliferative activity compared to SMBA1, with IC50 values of 3.22 μM and 0.07 μM against triple-negative breast cancer MDA-MB-231 and 3.81 μM and 0.06 μM against ER-positive breast cancer MCF-7 cell lines, respectively. Mechanism of action studies of compound 49 indicated that it can activate Bax protein to induce cytochrome c release and regulate apoptotic biomarkers, leading to cancer cell apoptosis. Further in vivo efficacy studies of compounds 14 and 49 in nude mice bearing MDA-MB-231 tumor xenografts demonstrated that these drug candidates can significantly suppress tumor growth, indicating their therapeutic potential for the treatment of breast cancer.

Electronic and optical characteristics of phosphorus-doped carbon nanotubes: a first principle study

The electronic and optical properties of pure, phosphorus doped infinite and finite single walled carbon nanotubes (n, 0) (n = 4, 5 and 6) with different doping degree were investigated with the combination of density functional theory (DFT) and Non-Equilibrium Green’s function (NEGF) formalisms at room temperature. It was found that depending on the chirality, phosphorus atoms may eliminate the Van Hove Singularity energy or increase the density of states (DOS) at Fermi level. Also, replacing the carbons by phosphorus atoms increases DOS at Fermi level. The π bonds between carbon and phosphorus are responsible for extraordinary DOS at Fermi level as well. Moreover, each P atom in the simulated tubes contains about 2.62e-2.94e. Replacing carbon atoms by phosphorus eventuates in the reduction of optical susceptibility and the statics refractive index. Last but not least, despite pure SWCNTs, the doping results in the lower static refractive index as well as the increment of an intraband optical gap for the parallel to tube axis polarization through P-SWCNTs.

Bandgap opening in graphene using alkali ions by first principles

Recently, bandgap opening at the Dirac point in graphene, formed on SiC(0001) surfaces, has been reported in different experiments, by deposition of positively charged alkali ions. This is clearly of great relevance for the countless practical applications of graphene in nano-electronic devices. By first principles calculations, based on the Density Functional Theory, the electronic band structure and the energetic properties are obtained for Na+, K+, and Cs+ ions interacting with graphene on SiC. We show that simple adsorption of alkali ions on intact graphene cannot give rise to a significant energy gap. An appreciable bandgap opening, similar to that observed in actual experiments, occurs instead due to the formation of Stone-Wales defects and substitutional defects (where positively charged alkali ions replace carbon atoms) that lead to a significant breaking of the charge symmetry among the carbon atoms of pristine graphene.