Yuanhe Huang

Structures and stabilities of C60-rings

Abstract A method to construct various C60-rings is given. 36 C60-rings with D n h and C n v symmetries have been investigated using self-consistent-field molecular orbital method. Their stabilization energies (E) are mainly affected by the distortion of the C60 balls (σ), the number of double bonds introduced into pentagons per C60 (j) and the number of formed intermolecular bonds (k). Their electronic properties are discussed and compared with those of single C60.

Structure and electronic properties of the double-wall nanotubes constructed from SiO2 nanotubes encapsulated inside zigzag carbon nanotubes

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 SiO(2) 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 10(2)-10(4) cm(2) V(-1) s(-1), the same order of magnitude as those of the corresponding zigzag carbon nanotubes. The Youngs moduli are also calculated for the combined systems.

Electronic properties of one-dimensional C36 polymers

Electronic structures for several neutral and anionic one-dimensional (1D) C36 polymers are investigated by using the ab initio self-consistent-field crystal orbital method based on the B3LYP (Becke–Lee–Yang–Parr) density functional theory. Calculations show that all the neutral polymers are semiconductors with energy gaps in the range from 0.55 to 2.04 eV. The possibilities of superconducting and Peierls phase transitions are also explored for these metallic anionic polymers at the same time. It is found that the intramolecular electron–phonon (e–p) coupling in metallic 1D C36 polymers plays an important role in producing high superconducting transition temperatures (Tc). The estimated Peierls phase transition temperatures (Tp) are very small due to the very weak intermolecular e–p interactions.

Structures and stabilities of C36-rings

Abstract C36-rings with Dnh symmetries have been investigated using the semi-empirical molecular orbital method (AM1). The ring structures are beneficial to the stability of the C36 systems. An analysis of several factors, such as the change in strain energies due to the distortion of C36 cages, the type of the bonded carbon atoms, the size of retained aromatic domains and the shared pentagon–pentagon double bonds, is given for their contributions to stabilities of the C36-rings. The electronic properties are also discussed and compared with those of C60-rings.

Electronic Property Modulation of One‐Dimensional Extended Graphdiyne Nanowires from a First‐Principle Crystal Orbital View

Abstract Graphdiyne and derivatives with delocalized π‐electron systems are of particular interest owing to their structural, electronic, and transport properties, which are important for potential applications in next‐generation electronics. Inspired by recently obtained extended graphdiyne nanowires, explorations of the modulation of the band gap and carrier mobility of this new species are still needed before application in device fabrication. To provide a deeper understanding of these issues, herein we present theoretical studies of one‐dimensional extended graphdiyne nanowires using first‐principle calculations. Modulation of the electronic properties of the extended graphdiyne nanowire was investigated systemically by considering several chemical and physical factors, including electric field, chemical functionalization, and carbo‐merization. The band gap was observed to increase upon application of an electric field parallel to the plane of the synthesized graphdiyne nanowire in a non‐periodic direction. Although chemical functionalization and carbo‐merization caused the band gaps to decrease, the semiconducting property of the nanowires was preserved. Band gap engineering of the extended graphdiyne nanowires was explored regarding the field strength and the number of −C≡C− units in the carbon chain fragments. The charge carrier mobility of chemically functionalized and carbo‐merized extended graphdiyne nanowires was also calculated to provide a comparison with pristine nanowire. Moreover, crystal orbital analysis was performed in order to discern the electronic and charge transport properties of the extended graphdiyne nanowires modified by the aforementioned chemical and physical factors.

Investigation of the change in band structure of a carbon nanotube due to a distortion keeping the initial translational symmetry

Abstract The changes in the band structure of a carbon nanotube due to a structural distortion keeping the initial translational symmetry were studied using a tight-binding model. From analytical expressions obtained for the energy bands, it was found that the distortion cannot cause a metal-insulator transition for a metallic armchair tube. However, it can open up an energy gap for a zigzag tube.

Crystal orbital studies on the 1D silic-diyne nanoribbons and nanotubes.

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 Youngs modulus and the Poissons ratio.

Octacoordinate Carbons Encaged Inside Carborane Clusters: A Density Functional Theory Investigation

This work focuses on the computational design and characterization of a novel series of endohedral carborane clusters containing octacoordinate carbon centers. The structural and bonding features and the thermodynamic and kinetic stabilities are discussed extensively based on density functional theory calculations. These nonclassical carboranes are fascinating in structure not only for the octacoordinate carbon center but also for the surrounding carbon and boron ligands with inverted bonding configuration. These endohedral carboranes are higher in energy than the corresponding exohedral isomers due to the high strain in the system. A new stability rule based on the donor-acceptor model is proposed to predict the stability ordering for these carborane isomers. In addition, some of these octacoordinate carboranes might have relatively high kinetic stabilities, which is rather hopeful for the experimental syntheses.

Molecular orbital study on antiferromagnetic coupling mechanism in a silver (I) complex

The mechanism of antiferromagnetic coupling in an Ag (I) complex of nitronyl nitroxide is investigated by means of the broken-symmetry approach within the density functional method (DFT-BS). The magneto-structural correlation and the single-occupied molecular orbital (SOMO) analysis reveal the existence of the antiferromagnetic coupling pathway along nitronyl nitroxide units via Ag (I) ion, and that the Ag (I) ion plays an important bridge role. The spin population analysis also shows the existence of spin delocalization along the ONCNO-Ag-ONCNO chain. It is found that the non-typical covalent bonds with major ionic character between Ag (I) ions and oxygen atoms of nitronyl nitroxide units can be used to mediate the spin-spin interaction of nitronyl nitroxides.

Stabilities and electronic properties of nanowires made of single atomic sulfur chains encapsulated in zigzag carbon nanotubes

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.