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Exploring at nanoscale from first principles
Qiang FU (付强), Lan-feng YUAN (袁岚峰), Yi LUO (罗毅), Jin-long YANG (杨金龙)
Frontiers of Physics in China. 2009, 4 (3 ): 256-268.
https://doi.org/10.1007/s11467-009-0057-z
Systems at the nanoscale can exhibit distinctive and unexpected properties in electrical, magnetic, mechanical, and chemical aspects. Understanding these properties not only is of importance from the fundamental scientific view but also offers great opportunities for future applications. Theoretical calculations can provide important information to interpret, modify, and predict the novel properties of objects at the nanoscale and therefore play a significant role in the process of exploring the nano world. In this review, six different areas are briefly presented, namely, prediction of new stable structures, modification of properties (especially the electronic structures), design of novel devices for applications, the structures and catalytic effects of clusters, the mechanical and transport properties of gold nanowires, and improvement of materials for hydrogen storage. Based on these examples, we show what can be done and what can be found in the investigations of nanoscale systems with participation of theoretical calculations.
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Studies on structural defects in carbon nanotubes
Hai-yan HE (何海燕), Bi-cai PAN (潘必才)
Frontiers of Physics in China. 2009, 4 (3 ): 297-306.
https://doi.org/10.1007/s11467-009-0021-y
Structural defects in carbon nanotubes (CNTs) have been paid much attention, because they influence the properties of the CNTs to some extent. Among various defects in CNTs, both single vacancies and Stone–Wales (SW) defects are the simple and common ones. In this paper, we review the progress of research in these two kinds of defects in CNTs. For single vacancies, we first address their different structural features in both zigzag and armchair CNTs, and their stabilities in CNTs with different sizes and different symmetries systematically. The presence of the single vacancies in CNTs not only influences the electronic structures of the systems, but also affects the vibrational properties of the tubes. Nevertheless, being active chemically, the single vacancies in the tubes prefer to interact with adsorbates nearby, of which the interaction of the defects with hydrogen atom, hydrogen molecule and some small hydrocarbon radicals (–CH, –CH2 and –CH3) are discussed. The former is associated with H storage and the latter is of merit to improve the local structure of the defect in a CNT. For the Stone–Wales defect, we mainly focus on its stability in various CNTs. The influence of the SW defects on the conductance of CNTs and the identification of such a defect in CNT is described in brief.
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Simulation of electronic structure of nanomaterials by central insertion scheme
Bin GAO (高斌), Jun JIANG (江俊), Yi LUO (罗毅)
Frontiers of Physics in China. 2009, 4 (3 ): 307-314.
https://doi.org/10.1007/s11467-009-0025-7
An effective central insertion scheme (CIS) that allows to study the electronic structure of nanomaterials at the first principles level is introduced. Taking advantage of advanced numerical methods, such as the implicitly restarted Arnoldi method (IRAM) and spectral transformation, together with efficient parallelization technique, this scheme can provide accurate electronic structures and properties of one-,two-, and three-dimensional nanomaterials with only a fraction of computational time required for conventional quantum chemical calculations. Electronic structures of several nanostructures, such as single-walled carbon nanotubes of sub-100 nm in length, silicon nanoclusters of sub-6.5 nm in diameter and metal doped silicon clusters, calculated at hybrid density functional level are presented.
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Single-electron tunneling and Coulomb blockade in carbon-based quantum dots
Wei FAN (樊巍), Rui-qin ZHANG (张瑞勤)
Frontiers of Physics in China. 2009, 4 (3 ): 315-326.
https://doi.org/10.1007/s11467-009-0023-9
Single-electron tunneling (SET) and Coulomb blockade (CB) phenomena have been widely observed in nanoscaled electronics and have received intense attention around the world. In the past few years, we have studied SET in carbon nanotube fragments and fullerenes by applying the so-called “Orthodox” theory [28]. As outlined in this review article, we investigated the single-electron charging and discharging process via current-voltage characteristics, gate effect, and electronic structure-related factors. Because the investigated geometric structures are three-dimensionally confined, resulting in a discrete spectrum of energy levels resembling the property of quantum dots, we evidenced the CB and Coulomb staircases in these structures. These nanostructures are sufficiently small that introducing even a single electron is sufficient to dramatically change the transport properties as a result of the charging energy associated with this extra electron. We found that the Coulomb staircases occur in the I -V characteristics only when the width of the left barrier junction is smaller than that of the right barrier junction. In this case, the transmission coefficient of the emitter junction is larger than that of the collector junction; also, occupied levels enter the bias window, thereby enhancing the tunneling extensively.
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Hydrogen adsorption and desorption on the Pt and Pd subnano clusters – a review
Liang CHEN (陈亮), Cheng-gang ZHOU (周成冈), Jin-ping WU (吴金平), Han-song CHENG (程寒松)
Frontiers of Physics in China. 2009, 4 (3 ): 356-366.
https://doi.org/10.1007/s11467-009-0050-6
In this review, we present our recent first principles studies on the sequential H2 dissociative chemisorption and H desorption on the Ptn and Pdn clusters (n =2-9, 13). Upon full saturation by H atoms, the calculated H2 dissociative chemisorption energy and H desorption energy on Pt13 and Pd13 clusters are similar to the corresponding values on smaller close-packed clusters. Indeed, the catalytic performances of these subnano clusters do not vary significantly with the particle sizes or shapes. Instead, they are dependent on the surface metal atoms which can be accessed by H atoms. In addition to the coverage dependency of the H2 dissociative chemisorption and H sequential desorption energies, the phase transition of both Pt13 and Pd13 from the icosahedral to fcc -like structures at certain H coverage was also investigated.
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Sidewall fluorination and hydrogenation of single-walled carbon nanotubes: a density functional theory study
Li-mei YU (于丽梅), Ji-jun ZHAO (赵纪军), Jie-shan QIU (邱介山), Ce HAO (郝策), Hai WANG (王海)
Frontiers of Physics in China. 2009, 4 (3 ): 393-397.
https://doi.org/10.1007/s11467-009-0051-5
The fluorination and hydrogenation reactions on (6, 6) and (10, 0) single-walled carbon nanotubes (SWCNTs) have been examined via computing the reaction energy for the chemisorption. The examined nanotubes have comparable lengths and diameters, with or without Stone–Wales defects on the sidewall. The two fluorine or hydrogen atoms are anchored to the external walls of the SWCNTs. The computed chemisorption energies of these virtual reactions reveal that the fluorination and hydrogenation of the nanotubes are moderately sensitive to the nanotube chirality and the sidewall topology, and the (10, 0) SWCNT with Stone–Wales defect can be easily fluorinated and hydrogenated.
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First-principles calculation on the conductance of ruthenium-quasi cumulene-ruthenium molecular junctions
Jing NING (宁静), Xin SHEN (沈昕), Zi-yong SHEN (申自勇), Xing-yu ZHAO (赵兴钰), Shi-min HOU (侯士敏)
Frontiers of Physics in China. 2009, 4 (3 ): 398-402.
https://doi.org/10.1007/s11467-009-0020-z
The conductance of a family of ruthenium-quasi cumulene-ruthenium molecular junctions including different numbers of carbon atoms, both in even numbers and odd numbers, are investigated using a fully self-consistent ab initio approach which combines the non-equilibrium Green’s function formalism with density functional theory. Our calculations demonstrate that although the overall transport properties of the Ru-quasi cumulene-Ru junctions with an even number of carbon atoms are different from those of the junctions with an odd number of carbon atoms, the difference between the corresponding currentvoltage (I -V ) characteristics of these molecular junctions declines to lesser than 16% when the voltage goes up. In each group, the molecular junctions give a large transmission around the Fermi level since the Ru-C π bonds can extend the π conjugation of the carbon chains into the Ru electrodes, and their I -V characteristics are almost linear and independent of the chain length, illustrating potential applications as conducting molecular wires in future molecular electronic devices and circuits.
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A first-principles study on the electronic structure of one-dimensional [TM(Bz)]∞ polymer (TM= Y, Zr, Nb, Mo, and Tc)
Fang WU (吴芳), Richard TJORNHAMMAR, Er-jun KAN (阚二军), Zhen-yu LI (李震宇)
Frontiers of Physics in China. 2009, 4 (3 ): 403-407.
https://doi.org/10.1007/s11467-009-0054-2
A systematic density functional theory (DFT) study has been performed to investigate the electronic and magnetic properties of one-dimensional sandwich polymers constructed with benzene (Bz) and the second-row transition metal (TM= Y, Zr, Nb, Mo, and Tc). Within the framework of generalized gradient approximation (GGA), [Tc(Bz)]∞ is a ferromagnetic half-metal, and [Nb(Bz)]∞ is a ferromagnetic metal. With the on-site Coulomb interaction for 4d TM atoms being taken into account, [Tc(Bz)]∞ keeps a robust half-metallic behavior, while [Nb(Bz)]∞ becomes a spin-selective semiconductor. The stability of the half-metallic [Tc(Bz)]∞ polymer is discussed based on magnetic anisotropy energy (MAE). Compared with 0.1 meV per metal atom in [Mn(Bz)]∞ , the calculated MAE for [Tc(Bz)]∞ is 2.3 meV per metal atom. Such a significantly larger MAE suggests that Tc(Bz)]∞ is practically more promising than its first-row TM equivalent.
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Simulations of inelastic electron tunneling spectroscopy of semifluorinated hexadecanethiol junctions
Chuan-kui WANG (王传奎), Bin ZOU (邹斌), Xiu-neng SONG (宋秀能), Ying-de LI (李英德), Zong-liang LI (李宗良), Li-li LIN (蔺丽丽)
Frontiers of Physics in China. 2009, 4 (3 ): 415-419.
https://doi.org/10.1007/s11467-009-0035-5
The inelastic electron tunneling spectroscopy (IETS) of semifluorinated hexadecanethiol junctions is theoretically studied. The numerical results show that the C–F vibration modes of semifluorinated alkanethiol series can not be detected, and the C–H stretching mode in IETS is related to the CH2 vibration. It is demonstrated that the Raman modes are preferred over IR modes in IETS, which is in good agreement with the experimental measurements presented by Beebe et al . [Nano Lett., 2007, 7(5): 1364].
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