Chuan-Lu Yang

First-principles study of structure and quantum transport properties of C20 fullerene

Using first-principles density-functional theory and nonequilibrium Greens function formalism for quantum transport calculation, we study the electronic and transport properties of C(20) fullerene molecule. Our results show that the equilibrium conductance of C(20) molecule is near 1G(0). It is found that the I-V curve displays a linear region centered about V = 0 and nonlinear behavior under higher bias voltages and an obvious negative differential resistance phenomenon in a certain bias voltage range. The mechanism for the negative differential resistance behavior of C(20) is suggested. The present findings could be helpful for the application of the C(20) molecule in the field of single molecular devices or nanometer electronics.

Effect of functionalization on the interfacial binding energy of carbon nanotube/nylon 6 nanocomposites: a molecular dynamics study

The critical challenge for preparing carbon nanotube (CNT)/polymer nanocomposites is how to create a strong interfacial binding energy (IBE) between the polymer matrix and the CNT. Molecular dynamics simulations of nylon 6 melts and its composite with pristine CNT or functionalized CNT embedded have been performed. The properties of the nanocomposites are investigated with the IBE between CNT and nylon 6. The non-bond energies from both vdW and electrostatic interactions, are calculated for nylon 6 and CNT functionalized by different groups. Our calculational results show that the vdW interaction energies of all the functionalized CNT/nylon 6 composites are close to that of the pristine CNT/nylon 6 composite, implicating the electrostatic interactions are responsible for the strong IBE of the functionalized CNT/nylon 6 composites. Therefore, the functionalized CNT can expand the application of polymer in actual production.

Quasi-classical Trajectory Study of the Ne + H2 + → NeH+ + H Reaction Based on Global Potential Energy Surface

Using the multireference configuration interaction method with a Davidson correction and a large orbital basis set (aug-cc-pVQZ), we obtain an energy grid that includes 32 038 points for the construction of a new analytical potential energy surface (APES) for the Ne + H(2)(+) → NeH(+) + H reaction. The APES is represented as a many-body expansion containing 142 parameters, which are fitted from 31 000 ab initio energies using an adaptive nonlinear least-squares algorithm. The geometric characteristics of the reported APES and the one presented here are also compared. On the basis of the APES we obtained, reaction cross sections are computed by means of quasi-classical trajectory (QCT) calculations and compared with the experimental and theoretical data in the literature.

Ab initio study of lutetium dimer

The ab initio quadratic CI calculation method and the effective-core-potential basis set have been used to calculate the equilibrium geometries, potential energy curves, dissociation energies of the ground state, and low-lying electronic states of Lu2 for the first time. The symmetries of these states are determined by analyzing the potential energy curves and optimization calculations at the same time. The analytical potential energy functions of these states have been fitted with the Murrell–Sorbie potential energy function from the calculated values with the ab initio method. The spectroscopic parameters of each state are calculated through the relationship equations between analytical potential energy function and spectroscopic parameters, and are compared with some other theoretical and experimental data available from the experiment at present. For the ground state, we obtain the symmetry is X 3Σg, ωe=113.3 cm−1 with ωeχe=0.16 cm−1, leading to a spectroscopic dissociation energy of 1.79 eV. They are...

Intrinsic negative differential resistance characteristics in zigzag boron nitride nanoribbons

We investigate the charge transport properties of zigzag boron nitride nanoribbons (ZBNNRs) with various hydrogen passivations by employing density functional theory (DFT) combined with the non-equilibrium Greens function (NEGF) formalism. The calculated results reveal that the ZBNNR-based devices exhibit negative differential resistance (NDR) characteristics except those models whose both edges are passivated, due to the mechanism in which the overlap of bands near the Fermi level between the left and right electrodes gets smaller or disappears under a high bias. The NDR characteristics of the perfect ZBNNRs with one or two bare edges are weakly dependent on their widths. This is one intrinsic NDR characteristic of the ZBNNR-based devices, including some defective structures. The intuitive electronic current channels are plotted and analyzed to better understand the charge transport mechanisms. Our results suggest that the ZBNNR-based structures could be favorable candidates for preparing nanoscale NDR devices.

A new analytical potential energy surface for the singlet state of He2H

The analytic potential energy surface (APES) for the exchange reaction of HeH(+) (X(1)Σ(+)) + He at the lowest singlet state 1(1)A(∕) has been built. The APES is expressed as Aguado-Paniagua function based on the many-body expansion. Using the adaptive non-linear least-squares algorithm, the APES is fitted from 15 682 ab initio energy points calculated with the multireference configuration interaction calculation with a large d-aug-cc-pV5Z basis set. To testify the new APES, we calculate the integral cross sections for He + H(+)He (v = 0, 1, 2, j = 0) → HeH(+) + He by means of quasi-classical trajectory and compare them with the previous result in literature.

Excited-state hydrogen bonding dynamics of methyl isocyanide in methanol solvent: A DFT/TDDFT study

The time-dependent density functional theory (TDDFT) method was performed to investigate the hydrogenbonding dynamics of methyl cyanide (MeNC) as hydrogen bond acceptor in hydrogen donating methanol (MeOH) solvent. The ground-state geometry optimizations and electronic transition energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated MeNC and MeOH monomers, the hydrogen-bonded MeNC-MeOH dimer and MeNC-2MeOH trimer are calculated by the DFT and TDDFT methods, respectively. An intermolecular hydrogen bond N≡C…H-O is formed between MeNC and methanol molecule. According to Zhao’s rule on the excited-state hydrogen bonding dynamics, we find the intermolecular hydrogen bonds N≡C…H-O are strengthened in electronically excited states of the hydrogen-bonded MeNC-MeOH dimer and MeNC-2MeOH trimer, with the excitation energy of a related excited state being lowered and electronic spectral redshifts being induced. Furthermore, the hydrogen bond strengthening in the electronically excited state plays an important role on the photophysics and photochemistry of MeNC in solutions

Theoretical characteristics of the bound states of M-X complexes (M=Cu, Ag, and Au, and X=He, Ne, and Ar)

The potential energy curves (PECs) of the bound states of M-X (M=Cu, Ag, and Au and X=He, Ne, and Ar) complexes have been calculated using the coupled cluster singles and doubles method with perturbative treatment of triple excitations. Large basis sets and bond functions, as well as the basis set superposition errors, are employed to obtain accurate PECs. The analytical potential energy functions (APEFs) are fitted using the PECs. The vibrational energy levels and the spectroscopic parameters for the complexes are determined using our APEFs and compared to the theoretical works available at present. We also find that the PECs are bound with similar van der Waals interactions, which implies that He, Ne, and Ar may be used for buffer-gas cooling; and Cu, Ag, and Au may be trapped with a similar method because Cu and Ag have been experimentally trapped with He buffer-gas cooling.

The peculiar electronic structure of the di-metallocene: The evidence for the stability and the character of metal-metal bond

Quantum chemical density functional theory (DFT) calculations using B3LYP and BP86 functionals have been carried out for the di-metallocene complexes. The equilibrium geometries and the bond characters have been reported. The calculations of Cp2Zn2, Cp2Cd2 and Cp2Hg2 demonstrate that the di-metallocene complexes slightly favor D5h conformations for the free molecules, where Cp is C5H5. The predicted Cd-Cd distance of 2.723 A and Hg-Hg distance of 2.826 A are indicative of substantial Cd-Cd and Hg-Hg bonds. In this work, we have reported DFT MO energy level diagrams for the di-metallocene complexes. The strong interaction between Cp and Zn atoms is mainly due to the π orbital of the Cp and the s and dz2 orbitals of the Zn atom. The metal–metal bonds were studied in detail. The results indicated that there are two δ, one σ and two π interactions between five d orbitals and one σ interaction between s orbitals of the two metal atoms. The electron configurations are pictured as , and so the bond order is determined by the molecular orbital theory, which is in agreement with the NBO analysis that shows that each metal atom has one covalent bond (to the other metal atom) and a nearly pure s character of metal–metal bonds. At last, from the behavior of the HOMO and HOMO-LUMO gap, the order of the stability of those di-metallocene complexes is Cp2Zn2 > Cp2Cd2 > Cp2Hg2.

An ab initio study of the ground and low-lying excited states of KBe with the effect of inner-shell electrons

The potential energy curves (PECs) of 1(2)Σ(+), 2(2)Σ(+), 1(2)Π, and 2(2)Π states of KBe are calculated using multireference configuration interaction method and large all-electron basis sets. Four sets of frozen core orbitals (FCOs) are considered to examine the effect of inner-shell correlation electrons on the molecular properties. The ro-vibrational energy levels are obtained by solving the Schrödinger equation of nuclear motion based on the ab initio PECs. The spectroscopic parameters are determined from the ro-vibrational levels with Dunham expansion. The PECs are fitted into analytical potential energy functions using the Morse long-range potential function. The dipole moment functions of the states for KBe calculated with different FCOs are presented. The transition dipole moments for KBe between 1(2)Σ(+) and 2(2)Σ(+) states, 1(2)Π and 1(2)Σ(+) states, and 2(2)Π and 1(2)Σ(+) states are also obtained.