Mei-Shan Wang

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.

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 31u2009000 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.

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.

Quasi-classical trajectory study of the N(2D) + H2(X1ΣG+) → NH(X3Σ-) + H(2S) reaction based on an analytical potential energy surface.

Using the multireference configuration interaction method with the Davidson correction and a large orbital basis set (aug-cc-pV5Z), we obtain an energy grid that includes 17,500 points for the construction of a new analytical potential energy surface (APES) for the N((2)D) + H(2)(X(1)Σ(g)(+)) → NH(X(3)Σ(-)) + H((2)S) reaction. The APES, which contains 145 parameters and is represented with a many-body expansion and a new switch function, is fitted from the ab initio energies using an adaptive nonlinear least-squares algorithm. The geometric characteristics of the reported APES in the literature and those of our APES are also compared. On the basis of the APES that we obtained, reaction cross sections are computed by means of quasi-classical trajectory calculations and compared with the experimental and theoretical values available in the literature.

Density Functional Theory Studies of Aun+(CH3OH)m (n = 3, 5, m = 1−5) Complexes

The structural, energetic, and electronic properties of gold ions adsorbed methanol, Au(3)(+)-(CH(3)OH)(m) (m = 1-3) and Au(5)(+)-(CH(3)OH)(m) (m = 1-5), have been investigated using density functional theory (DFT) within a generalized gradient approximation (GGA). The geometric parameters, vibrational frequencies, adsorption energies, and Mulliken charges are used to analyze the interactions between Au(3,5)(+) clusters and methanol molecules. The present calculations show that more than one methanol molecule can be adsorbed onto small clusters of gold ions and that this adsorption is different from that of single-molecule absorption. The red shift of the C-O stretching frequency decreases as the number of methanol molecules, m, increases or as gold cluster size increases. The positive charge on Au(3,5)(+) and coordination number of the adsorption sites on the gold cluster are the dominant factors responsible for the strength of the interactions. We obtained C-O stretching frequencies in Au(1,2)(+)-(CH(3)OH) complexes that are below 931 cm(-1), which provides theoretical evidence for the experimental observation by Dietrich et al. [J. Chem. Phys. 2000, 112, 752].

Structural, Electronic, and Magnetic Properties of Fe3C2 Cluster

On the basis of density-functional theory and all-electron numerical basis set, 20 stable isomers of Fe(3)C(2) cluster are found through optimization calculations and frequency analysis from 108 initial structures. A nonplanar C(s) structure with nonet spin multiplicity and 482.978 kcal/mol of binding energy is found as the candidate of global minimum geometry of Fe(3)C(2) cluster. The binding energies, the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and the magnetic moments of all the isomers are reported. The relationship between the molecular properties and geometrical structures is also investigated.

Concerted Mechanisms of Excited-State Proton Intramolecular Transfer for Bis-2,4-(2-benzoxazolyl)-hydroquinone and Its Derivatives

The concerted mechanisms of excited state intramolecular proton transfer (ESIPT) of bis-2,4-(2-benzoxazolyl)-hydroquinone (BBHQ) and its derivatives (BBHQ- and DHBO) have been investigated using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT). The calculated absorption and emission spectra of BBHQ and its derivatives are in good agreement with the experimental results. The calculated bond lengths, bond angles, and IR vibrational spectra linked with hydrogen bond of molecular BBHQ in the S0 and S1 states demonstrate that the hydrogen bond is strengthened in the S1 state. Compared to BBHQ, BBHQ- has a weak change of hydrogen bond between the S1 and S0 states. The calculation results show that there are three stable structures of BBHQ in the S1 state. We find that the structure corresponding to the 481 nm fluorescence spectrum corresponds to BBHQ-A rather than BBHQ--K (Tetrahedron Lett., 2016, 57, 3518). The calculated frontier molecular orbitals (MOs) indicate the nature of the charge distribution and the trend of proton transfer of BBHQ-A. The constructed potential energy surfaces of BBHQ and DBHO further elucidate the proposed mechanism that one-proton or two-proton transfer can happen (stepwise or synchronous) in the S1 states. The proposed ESIPT mechanism can provide a good explanation of the phenomenon of fluorescence quenching of BBHQ and its derivatives. Finally, the weak interaction types are discriminated through the reduced density gradient (RDG) analyses of BBHQ and BBHQ-.

MRCI potential energy curves and analytical potential energy functions for the X2\sum+ and 2\prod states of BO molecule

The potential energy curves (PECs) of BO molecule, including sum+ and prod symmetries with doublet spin multiplicities, are obtained employing multi-reference configuration interaction (MRCI) method and Dunnings correlation consistent basis sets. The analytical potential energy functions (APEFs) are fitted using the Murrell-Sorbie (MS) function and the least square method. Based on the PECs, the spectroscopic constants of the states have been determined and compared with the theoretical and experimental results available to affirm the accuracy and liability of the calculations. The root-mean-square (RMS) errors between the fitted results and the ab initio values are too little in comparison with the chemical accuracy (349.755 cm-1. It is shown that the present APEFs are accurate and can display the interaction between the atoms well. The present APEFs can be used to construct more complicated APEF or do some dynamic investigations.

The Mechanism of Fluorescence Quenching by Acylamino Twist in the Excited State for 1-(Acylamino)anthraquinones

Nitrogen-containing anthraquinone derivatives are widely applied in vegetable fiber dyes. In this paper, the fluorescence quenching mechanism by an acylamino group twist in the excited state for the 1-(acylamino)anthraquinones (AYAAQs) derivatives in acetonitrile is investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The calculated Stokes shift is in good agreement with the experimental data. The energy profiles show that each AYAAQs derivative reveals a barrierless twist process, indicating that the involvement of acylamino group rotation in addition to proton transfer becomes as another important coordinate in the excited state relaxation pathway. The effects of electron-substituted group promote twist process compared with 1-aminoanthraquinone (AAQ). Then, the cross points are searched by the constructed linearly interpolated internal coordinate (LIIC) pathways for AYAAQs, demonstrating that the potential energy curves of the S1 and T2 states intersect each other and are in accord with the El-Sayed rules. So one can conclude that the acylamino group twist and following intersystem crossing (ISC) processes are important nonradiative inactivation channel for the S1 state of the AYAAQs derivatives, which is more prone to proton transfer process and can explain the low fluorescence efficiency. In addition, we have measured the phosphorescence spectra of AAQ, and on this basis, it can be predicted that the phosphorescence may occur for the AYAAQs derivatives.

Ab initio Studies on Spectroscopic Constants for the HAsO molecule

The anharmonic force fields and spectroscopic constants of the electronic ground state (X̃1A) for the HAsO molecule are reported employing the MP2, B3LYP, B3P86, and B3PW91 methods with cc-pVQZ and cc-pV5Z basis sets. The calculated molecular geometries, rotational constants, vibrational frequencies, and anharmonic constants of the HAsO molecule are compared with the experimental data. It is found that the best agreement between the calculated results and experiment data is at the B3LYP/cc-pV5Z theoretical level. The predicted cubic and quartic force fields, vibration-rotation interaction constants, quartic and sextic centrifugal distortion constants, and Coriolis coupling constants of the HAsO molecule at the B3LYP/cc-pV5Z theoretical level are expected to be reliable.