Dongmei Du

Studies on density functional theory for the electron-transfer reaction mechanism between M–C6H6 and M+–C6H6 complexes in the gas phase

Density functional theory (DFT) is used to theoretically investigate the electron-transfer (ET) reactions between M (Li, Na, Mg)–C6H6 and M+–C6H6 complexes in the gas phase. The geometry optimization of the metal–benzene complexes and the encounter state in the process of ET reaction was performed at the 6-31G basis set level. The metal atoms (or metal ions)–benzene molecule separation distances computed using DFT method were found to agree with second-order Moller–Plesset (MP2) results. The precursor complex has C6 symmetry, the distances between acceptor and donor is about 3.0–3.6 A, which yields a bonding energy of approximately 0.9–1.5 eV. It shows there are relatively strong interactions between them. Additionally, the geometry of transition state is also obtained by the linear coordinate method. From the analysis of the charge on the transition state and the isolated state, the reaction mechanism was derived. Also the activation energy and the coupling matrix element of the rate constant of the ET reaction are calculated. According to the reorganization energy of the ET reaction, the values obtained from George–Griffith–Marcus (GGM) method (the contribution only from diagonal elements of force constant matrix) are larger than those obtained from Hessian matrix method (including the contribution from both diagonal and off-diagonal elements), which suggests that the coupling interactions between different vibrational modes are important to the inner-sphere reorganization energy for the ET reactions in gaseous phase.

Calculation of the energy of activation in the electron transfer reaction not involving the bond rupture at the electrode

Abstract A new model of the free energy of activation in electron transfer reaction at the electrode is presented in this paper. The solvation process of an ion is considered and three accurate potential functions (Morse function, harmonic oscillator potential and modified harmonic oscillator potential function) are defined in terms of the experimental spectroscopic and solvation thermodynamic data. The activation energy is obtained in terms of the proposed model of the free energy of activation and the three potential functions. The theoretical values of the activation free energy agree well with the experimental results, these agreements take into account the validity of the new model.

Density functional theory study of vibrational spectra of acridine and phenazine.

Density functional theory (DFT) calculations using Beckes exchange in conjunction with Lee-Yang-Parrs correlation functionals (BLYP), Beckes three-parameter hybrid DFT/HF method using Lee-Yang-Parrs correlation functionals (B3LYP) and ab initio Hartree-Fock (HF) method have been carried out to investigate the structure and vibrational spectra of acridine and phenazine. Structural parameters obtained by B3LYP/6-31G* geometry optimization are in good agreement with available experimental data. The raw BLYP non-CH stretching frequencies approximate the experimental results much better than the HF results with the mean absolute deviation about 16 cm(-1). The scaled B3LYP frequencies are more reliable than that of the BLYP and HF methods with the mean absolute deviation about 17 cm(-1). On the basis of the comparison between calculated and experimental results, assignments of fundamental vibrational modes are examined. Also the structure and vibrational frequencies are compared with those of anthracene, pyridine and benzene to study the similarities and differences.

Structures and vibrational frequencies of pyruvic acid: density functional theory study

Abstract Density functional theory BLYP (using Beckes exchange and Lee–Yang–Parrs correlation functionals ), ab initio Hartree–Fock (HF) and hybrid DFT/HF B3LYP calculations were carried out to study the structure and vibrational spectra of pyruvic acid. Molecular conformation calculations were made for two possible conformers (eclipsed and staggered of C4O8 bond with respect to the methyl group) of the compound. Calculated results show that the stable conformer of pyruvic acid is the eclipsed one. The raw BLYP and B3LYP frequencies approximate the experimental results much better than the Hartree–Fock results, the scaled B3LYP results are more reliable than that of the BLYP and HF methods with the mean absolute deviation about 12.3 cm −1 . On the basis of the comparison between calculated and experimental results, assignments of fundamental vibrational modes are examined.

Cellobiose as a model system to reveal cellulose dissolution mechanism in acetate-based ionic liquids: Density functional theory study substantiated by NMR spectra.

Cellulose dissolution mechanism in acetate-based ionic liquids was systematically studied in Nuclear Magnetic Resonance (NMR) spectra and Density Functional Theory (DFT) methods by using cellobiose and 1-butyl-3-methylimidazolium acetate (BmimAc) as a model system. The solubility of cellulose in ionic liquid increased with temperature increase in the range of 90-140°C. NMR spectra suggested OAc(-) preferred to form stronger hydrogen bonds with hydrogen of hydroxyl in cellulose. Electrostatic potential method was employed to predict the most possible reaction sites and locate the most stable configuration. Atoms in molecules (AIM) theory was used to study the features of bonds at bond critical points and the variations of bond types. Simultaneously, noncovalent interactions were characterized and visualized by employing reduced density gradient analysis combined with Visual Molecular Dynamics (VMD) program. Natural bond orbital (NBO) theory was applied to study the noncovalent nature and characterize the orbital interactions between cellobiose and Bmim[OAc].

Experiment and DFT studies on radioiodine removal and storage mechanism by imidazolium-based ionic liquid

In order to remove and store radioactive substances effectively, studies on the mechanisms of radioiodine captured by ionic liquids (ILs) with a fixed cation (1-butyl-3-methyl-imidazolium cation [Bmim]+) were carried out in experimental and theoretical methods. Fourier transform infrared attenuated total reflectance (FT-IR ATR) spectra of 2BP8HQ and ultraviolet-visible (UV/vis) spectroscopy were used to investigate the kinetic process of radioiodine removal by ILs in experiment. Corresponding theoretical investigations on the structures and formation mechanisms of ILs, bare anions and complexes as well as hydrogen bonds was carried using density functional theory. The electrostatic potential was used in configuration design and construction. Charge distribution was used to show the variation of atom charge density, Interaction energy and vibration frequency change were performed to explore possible mechanisms on the halogen bond formation between radioiodine molecule and bare anion or anion in ILs when radioiodine captured by ILs. In order to characterize halogen bonds both natural bond orbital analysis and atoms in molecules analysis were performed. Both experimental and computational results showed that radioiodine could be captured by ILs with a 1:1mol stoichiometry. It was noteworthy that [Bmim][Br], [Bmim][I] and [Bmim][Cl], containing high radioiodine capture efficiency anions, were better candidates in removal and reliable storage of radioiodine for their capture efficiencies of over 80% in 5h.

Density functional theory study on the structure and vibrational spectra for 4-methyl-3-pentene-2-one

Density functional theory BLYP (using Beckes and Lee–Yang–Parrs correlation functionals), ab initio Hartree–Fock (HF) and hybrid DFT/HF B3LYP calculations were carried out to study the structure and vibrational spectra of s-cis-4-methyl-3-pentene-2-one. Molecular conformation calculations were made for four possible conformers of the compound using the HF and BLYP methods. Calculated results show that: (1) the stable conformer of the 4-methyl-3-penten-2-one is s-cis; (2) the BLYP/6-31G∗ and scaled HF/6-31G∗ frequencies correspond well with each other and with available experimental assignment of the normal vibrational modes.

Theoretical investigation of the conformation for 2-butanimine

The molecular structure and conformational stability of 2-butanimine have been investigated using ab initio and density functional theory methods. The molecular geometries for various conforms are optimized employing MP2, BLYP, and B3LYP methods implementing 6-311++G∗∗ basis sets. From the calculations, the molecules are predicated to exist in four stable conformers with the (E)-sp form being slightly lowers in energy than the other ones. The vibrational frequencies for the four conforms are computed at different levels and compared to the fundamental values. The results indicate that B3LYP frequencies reproduce the experimental values satisfactorily. On the basis of the comparison between calculated and experimental results, the fundamental vibrational modes are assigned. Through the analysis of the vibrational modes and frequencies for the four conformers, we can conclude that the vibrational quantum number ν is a crucial variable to get reasonable energy difference between various conformations.

Structure and vibrational frequencies of 2-butanimine

The conformational behavior and structural stability of 2-butanimine were investigated by utilizing ab initio calculations with 6-311++G** basis set at HF, MP2, B3LYP and BLYP levels. The vibrational frequencies of 2-butanimine were computed. Complete vibrational assignments were made on the basis of normal coordinate calculations for stable conformer of the molecule. HF results without scaled quantum mechanical (SQM) force field procedure considered are in bad agreement with experimental values. Of the two DFT methods, BLYP reproduces the observed fundamental frequencies most satisfactorily with the mean absolute deviation of the non-CH stretching modes less than 21.3 cm(-1). The results indicate that BLYP calculation is a very promising approach for understanding the observed spectral features.