[en] This paper presents ab initio self-consistent field crystal orbital calculations on the structures, stabilities, elastic and electronic properties of the double-wall nanotubes made of SiO₂ nanotubes encapsulated inside zigzag carbon nanotubes based on density functional theory. It is found that formation of the combined systems is energetically favorable when the nearest distance between the two constituents is in the area of the van der Waals effect. The obtained band structures show that all the combined systems are semiconductors with nonzero energy gaps. Based on the deformation potential theory and effective mass approximation, the mobilities of charge carriers are calculated to be in the range of 10²-10⁴ cm ² V ^-1 s ^-1, the same order of magnitude as those of the corresponding zigzag carbon nanotubes. The Young’s moduli are also calculated for the combined systems. (paper)

[en] Structures, stabilities, electronic properties and carrier mobilities of 6,6,12-graphyne nanoribbons (GyNRs) with armchair and zigzag edges are investigated using the self-consistent field crystal orbital method based on density functional theory. It is found that the 1D GyNRs are more stable than the 2D 6,6,12-graphyne sheet in the view of the Gibbs free energy. The stabilities of these GyNRs decrease as their widths increase. The calculated band structures show that all these GyNRs are semiconductors and that dependence of band gaps on the ribbon width is different from different types of the GyNRs. The carrier mobility was calculated based on the deformation theory and effective mass approach. It is found that the carrier mobilities of these GyNRs can reach the order of 10"5 cm"2 V "–"1s"–"1 at room temperature and are comparable to those of graphene NRs. Moreover, change of the mobilities with change of the ribbon width is quite different from different types of the GyNRs

[en] Theoretical investigations are carried out on the recently synthesized one-dimensional nanowires made of atomic sulfur chains encapsulated in carbon nanotubes (called S@CNTs). Special attention is paid to stability, electronic property and transport properties of these combined nanowires. It is found that the encapsulation is exothermic when S@CNTs are built from the tubes with diameter larger than 6.4 Å. Thus the experimental results are energetically favorable since the diameters of the CNTs are about 6 Å in the obtained S@CNTs. The combined nanowires can be stabilized by van der Waals interaction between sulfur chain and tube as indicated from radial distribution function and reduced density gradient descriptions. All S@CNTs studied in this work exhibit metallic property with the partially filled bands. However, the conducting component and the pathway of charge carriers are various. For instance, only the sulfur chain is the conducting pathway for S@CNT(8, 0), while both the sulfur chain and tube are the conducting pathways for S@CNT(9, 0). This interesting feature was understood based on the band structures and crystal orbital analysis. The electronic transport properties of the systems are performed by investigating and analyzing the transmission spectra, current–voltage (I–V) curves and transmission eigenstate, which confirm that the sulfur chains can improve the electronic transport of CNTs. Moreover, the electrostatic interaction resulted from the charge transfer between the two components of S@CNTs should be favorable to the stability of the combined nanowires. (paper)

[en] Charge carrier mobility is a central transport property in nanoscale electronics. Carbon nanotubes (CNTs) are supposed to have high carrier mobility. The preparation methods of CNTs have been greatly improved, but the defects always exist. This work presented first-principle investigations on the charge carrier mobility of carbon nanotubes containing several intrinsic defects. The charge carrier mobilities of zigzag (10, 0) tubes with Stone–Wales, mono vacant and 5/8/5 defects were studied as an example to explore the role of defects. Most carrier mobilities were decreased, but several values of mobility are unexpectedly increased upon the appearance of the defects. This interesting result is discussed based on the changes of the stretching modulus, the effective mass of the carrier and deformation potential constant induced by the defects. (paper)

[en] This work presents crystal orbital studies on novel one-dimensional (1D) nanoscale materials derived from a Si-diyne sheet, based on the density functional theory. The two-dimensional (2D) Si-diyne layer is observed to be carbo-merized silicene, with a similar structure to graphdiyne. The 2D Si-diyne and its 1D ribbons and tubes, of different size and chirality, have been addressed systematically. The low dimensional Si-diyne materials studied exhibit relatively high stability, according to phonon-frequency calculations and molecular dynamics simulations. With comparable diameters, the Si-diyne tubes have lower strain energies than silicene and silicon carbide nanotubes. The Si-diyne layer and its 1D derivatives are all semiconductors, regardless of the size and chirality of the strips and tubes. In addition, the band gaps of the 1D Si-diyne nanoribbons and nanotubes with different chirality, always monotonically decrease as their sizes increases. A quantitative relationship between the band gap and the size of the ribbons and tubes was obtained. The mobility of charge carriers for the 1D Si-diyne structures was also investigated. It was found that both hole and electron mobility of the ribbons and tubes exhibit linear increase with increasing size. The electrons have greater mobility than the holes for each strip and tube. In addition, the mechanical properties of the Si-diyne nanostructures were also investigated by calculation of the Young’s modulus and the Poisson’s ratio. (paper)

[en] This article presents first-principles self-consistent-field crystal orbital calculations on the structures and electronic properties for the combined systems made of nitrogen atom chains inserted in zigzag carbon nanotubes (CNTs). We find that the nitrogen chains with the zigzag structure can be well stabilized by the outside CNTs. The molecular dynamics simulations based on density functional with tight binding method confirmed the stability of nitrogen chains under the confined conditions. Thus the zigzag CNTs can be as containers to confine and stabilize the polymeric nitrogen chains. According to the obtained binding energy, (9, 0) tube is the most favorable to filling the nitrogen chain. The combined systems are all metals except the filling into (7, 0) tube, indicating the encapsulation of the nitrogen chain can modulate the electronic properties for the combined systems. The interaction between the nitrogen chain and CNTs is also discussed based on the reduced density gradient, band structures and electronic density difference analysis. It is found that the van der Waals force, charge transfer and orbital interaction are all important for the formation of the combined systems.

[en] This work presents first-principle investigations into the charge carrier mobility of carbon nanotubes containing monovacancy or related defects. The pristine and defective zigzag (10, 0) tubes were selected to explore the role of defects on the charge carrier mobility. It was found that the electron mobility of one defective structure was unexpectedly increased, while most others were decreased upon the appearance of the defect. To further understand the modification of the carrier mobility induced by monovacancy or related defects, crystal orbital analysis was performed. It was observed that the vacancy defect plays an important role in the case of both increased and decreased mobility. The unusual increased carrier mobility was mainly derived from the weaker acoustic scattering due to the modified wave-function induced by the defect. As for the decreased carrier mobilities, the heavier carrier determined by localized wave-functions, caused by the defects, is the most important factor. (paper)

[en] The superhalogen properties of polynuclear structures without halogen ligand are theoretically explored here for several [M_2(CN)_5]"−"1 (M =  Ca, Be) clusters. At CCSD(T) level, these clusters have been confirmed to be superhalogens due to their high vertical electron detachment energies (VDE). The largest one is 9.70 eV for [Ca_2(CN)_5]"−"1 which is even higher than those of corresponding traditional structures based on fluorine or chlorine ligands. Therefore the superhalogens stronger than the traditional halogen-based structures could be realized by ligands other than halogen atoms. Compared with CCSD(T), outer valence Green’s function (OVGF) method either overestimates or underestimates the VDEs for different structures while MP2 results are generally consistent in the aspect of relative values. The extra electrons of the highest VDE anions here aggregate on the bridging CN units with non-negligible distribution occurring on other CN units too. These two features lower both the potential and kinetic energies of the extra electron respectively and thus lead to high VDE. Besides superhalogen properties, the structures, relative stabilities and thermodynamic stabilities with respect to the detachment of cyanide ligand were also investigated. The sum of these results identifies the potential of polynuclear structures with pseudohalogen ligand as suitable candidates with enhanced superhalogens properties

[en] The structure–property relationship of the nanopeapods—one dimensional (1D) C₆₀O polymer encapsulated in single-walled carbon nanotubes (SWCNTs)—is studied by means of the self-consistent field crystal orbital method. The calculations show that the nearest distance between the two constituents is within Van der Waals interaction scope in the most stable two peapods. The SWCNT sizes affect not only the stability but also the electronic structures of the peapods. The peapods with larger tube diameters keep the semiconductive and metallic properties of the corresponding pristine SWCNTs. These combination systems are stiffer than the corresponding SWCNTs due to larger Young's moduli. The magnitude order of the calculated mobility of charge carriers is in the range of 10²–10⁵ cm² V⁻¹ s⁻¹ for the peapods, indicating that the combined systems may be good high-mobility electronic materials. - Graphical abstract: Formation of the novel peapod—1D C₆₀O polymer encapsulated inside single-walled carbon nanotube. Highlights: ► Several novel peapods encapsulating one dimensional C₆₀O polymers are constructed. ► Interwall distance of the two most stable peapods is in the Van der Waals scope. ► All peapods studied are stiffer than the corresponding SWCNTs. ► These peapods have high mobilies—in the order of 10²–10⁵ cm² V⁻¹ s⁻¹.

[en] The four new modified nucleobases (NBs), 5-mC, 5-hmC, 5-fC and 5-caC, besides the regular adenine, thymine, cytosine, guanine and uracil, are important in expression and regulation of genetic information. These four new major NBs are all derived from base cytosine by adding various functional groups, and their identification from the regular ones are much desired currently. However, the four new major NBs interacted with graphene on its surface have not been well considered, though a number of studies of regular NBs adsorbed on low-dimensional carbon materials are available to identify different NBs. This work reveals the interaction between the four new major NBs and graphene nanoflake substrate by using first-principle calculations based on density functional theory. The structure, energy and non-covalent interaction of the graphene/NBs complex are calculated and explored in details. The energy decomposition analysis, reduced density gradient, charge transfer and projected density of states are also performed to investigate the nature of the interaction between NBs and graphene nanoflake. Electrostatic and orbital interaction are found to be important to stabilize the interaction between NBs and graphene nanoflake, though orbital interaction is less significant. It is very noticed that the proportion of dispersion interaction could be more than half of the sum attractive contributions. Thus, dispersion interaction is the most dominating factor in stabilizing graphene/NBs complexes. The results of reduced density gradient further confirm that the interaction between the graphene nanoflake and NBs is mainly the van der Waals type. Besides, much attention is paid to the interaction differences between the four new major NBs and the pristine cytosine, and the impact of the introduced functional groups of the four new major NBs on the structure, energy and interaction is also discussed.