Rui-Zhou Zhang

First-principles study of the electronic and optical properties of a new metallic MoAlB

The structural, elastic, electronic and optical properties of MoAlB were investigated by first-principles calculations. The hardness of MoAlB is 12.71 GPa, which is relatively softer and easily machinable compared to the other borides. The analysis of the band structure and density (DOS) of states indicates that MoAlB has a metallic nature. The analysis of the electron localization function (ELF) shows that the Mo-B bond is a polar covalent bond with a short distance, which may increase the stability of the compound. The calculation of the phonon frequencies confirms the dynamical stability of MoAlB. Optical properties of MoAlB are investigated. In the energy range up to ~19 eV, MoAlB possesses high reflectivity and has the strongest absorption in the energy range of 0–23.0 eV. In addition, the plasma frequency of MoAlB is 20.4 eV and MoAlB can change from a metallic to a dielectric response if the incident light has a frequency greater than 20.4 eV.

THEORETICAL STUDIES ON HEATS OF FORMATION FOR SOME THIOL COMPOUNDS BY DENSITY FUNCTIONAL THEORY AND CBS-Q METHOD

The heats of formation (HOFs) for 15 thiol compounds are calculated by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods with 6-311G** basis set and the complete basis set (CBS-Q) method. It is demonstrated that the B3P86 and CBS-Q methods are accurate to compute the reliable HOFs for thiol compounds. In order to test whether the B3P86 method has a low basis set sensitivity, the HOFs for six thiol compounds are also calculated by using the B3P86 method with 6-31+G*, 6-31+G**, and 6-311+G** basis sets for comparison. We also extend our study by employing the nonlocal BLYP method together with 6-31+G* basis set to calculate the HOFs for thiol compounds. The obtained results are compared with the experimental results. It is noted that the B3P86 method is not sensitive to the basis sets. Considering the inevitably computational cost of CBS-Q method and the reliability of the B3P86 calculation, the B3P86 method with a moderate or a larger basis set such as 6-311G** and 6-311+G** may be more suitable to calculate the HOFs of thiol compounds. In addition, we believe that the maximum error associated with the calculated HOFs is less than 6 kcal/mol for the B3P86/6-311G** method and it is expected that the error bar is more likely 1–5 kcal/mol for the HOFs of thiol compounds.

THEORETICAL CALCULATION OF BOND DISSOCIATION ENERGIES AND HEATS OF FORMATION FOR ALKYL NITRATE AND NITRITE COMPOUNDS WITH DENSITY FUNCTIONAL THEORY AND COMPLETE BASIS SET METHOD

The N–O bond dissociation energies (BDEs) and the heats of formation (HOFs) of alkyl nitrate and nitrite compounds in gas phase at 298.15 K were theoretically calculated. Density functional theory (B3LYP and PBE1PBE) with 6-311+g** and 6-311g** basis sets was employed. It is found that PBE1PBE functional has an average increased BDE of 4.03 kcal/mol from B3LYP functional. What is more, we find the reverse trend in ab initio approach, which is slightly smaller than PBE1PBE. The B3LYP functional is found to be sufficiently reliable to compute the BDEs of alkyl nitrate compounds without the presence of diffusion functions. The BDEs of alkyl nitrite compounds appear to be a constant. The functionals (B3LYP and PBE1PBE) with 6-311g** and 6-311+g** basis sets and CBS-4M ab initio method can all yield good results with respect to the experimental HOFs with the deviation less than 2.0 kcal/mol. As the number of methylene group increases, the HOFs of alkyl nitrate and nitrite compounds increase. In addition, the conclusion of Ventural et al. (J Phys Chem A105:9912, 2001 and Phys Lett245:488, 1995) is confirmed again by our computational results.

C54Si6 heterofullerene as a potential gas sensor for CO, NO, and HCN detection

The adsorption of CO, NO, and HCN molecules on the C54Si6 heterofullerene is investigated on the basis of density functional theory calculations to exploit its potential applications as a gas sensor. The C54Si6 heterofullerene has two highly stable isomers (named isomer-1 and isomer-2). We find that the toxic CO, NO, and HCN molecules are chemically adsorbed on isomer-1 with moderate adsorption energies and apparent charge transfer. The electronic properties of isomer-1 are significantly influenced by the CO, NO, and HCN adsorption, especially its electric conductivity. The recovery time of the isomer-1 sensor for CO, NO, and HCN at room temperature is estimated to be short due to the medium (optimal) adsorption energies, indicating that isomer-1 (i.e. the most stable configuration) of C54Si6 heterofullerene should be a good CO, NO, and HCN sensor. Similar analysis indicates that the isomer-2 of C54Si6 heterofullerene is a potential efficient gas sensor for NO detection.

Theoretical Study of the CCl Bond Dissociation Enthalpy and Electronic Structure of Substituted Chlorobenzene Compounds

Quantum chemical calculations were used to estimate the bond dissociation energies (BDEs) for 13 substituted chlorobenzene compounds. These compounds were studied by the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods together with 631G** and 6311G** basis sets. The results show that B3P86/6311G** method is the best method to compute the reliable BDEs for substituted chlorobenzene compounds which contain the CCl bond. It is found that the CCl BDE depends strongly on the computational method and the basis sets used. Substituent effect on the CCl BDE of substituted chlorobenzene compounds is further discussed. It is noted that the effects of substitution on the CCl BDE of substituted chlorobenzene compounds are very insignificant. The energy gaps between the HOMO and LUMO of studied compounds are also investigated and from this data we estimate the relative thermal stability ordering of substituted chlorobenzene compounds.

Quantum-chemical studies of the structure and performance properties of 5-(1,2,4-triazol-C-yl)tetrazol-1-ols

Density functional theory was used to investigate IR spectra, heat of formation, and thermal stability of three energetic 5-(1,2,4-triazol-C-yl)tetrazol-1-ol compounds substituted at position 5 of the triazole ring. The detonation velocity and pressure were evaluated by using the Kamlet–Jacobs equations based on the packed density and solid-state heat of formation. The bond dissociation energies for the weakest bonds were analyzed to investigate the thermal stability of the title compounds. IR analysis shows that there are four main characteristic regions for the three compounds. Detonation velocity and pressure of the nitro derivative are higher than those of known explosive HMX, while the same characteristics of the nitroamino and azido derivatives are comparable to those of HMX. Bond dissociation calculations show that the N(5)–N(7) bond is the trigger bond during pyrolysis for all three compounds and the order of their thermal stability is azido > nitroamino > nitro. In addition, the energy gaps between the HOMO and LUMO of the studied compounds were also investigated and the obtained conclusion consistent with that of bond dissociation energy analysis.

Theoretical investigation on vibrational spectra, first order hyperpolarizability and NBO analysis of 4-Phenylpyridinium hydrogen squarate

The vibrational frequencies of 4-Phenylpyridinium hydrogen squarate (4PHS) in the ground state have been investigated by using B3LYP/6-311++G(d,p) level. The analysis of molecular structure, natural bond orbitals and frontier molecular orbitals was also performed. The IR spectra were obtained and interpreted by means of potential energies distributions (PEDs) using MOLVIB program. NBO analysis proved the presence of C-H⋯O and N-H⋯O hydrogen bonding interactions, which is consistent with the analysis of molecular structure. The dipole moments and first-order hyperpolarizability (βtot) are calculated and are 5.856 D and 4.72×10(-30) esu, respectively. The high βtot value and the low HOMO-LUMO energy gap (4.062eV) are responsible for the optical and electron-transfer properties of 4PHS molecule. The photoresponse-related results indicate that 4PHS molecule is an excellent organic candidate of photon-responsive materials.

THEORETICAL STUDIES ON HEATS OF FORMATION OF PYRIDINE N-OXIDES USING DENSITY FUNCTIONAL THEORY AND COMPLETE BASIS METHOD

The heats of formation (HOFs) for 11 pyridine N-oxide compounds are calculated by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86, PBE1PBE) methods with 6-31G** basis set and ab initio CBS-4M method. It is demonstrated that the B3PW91 method is accurate to compute the reliable HOFs for pyridine N-oxide compounds. It is also noted that the HOF is the smallest for the pyridine N-oxide which has the substituent group on the para-position, such as 4-NC–c-C5H4NO, 4-H2NOC–C5H4N–O, and 4-HO2C–c-C5H4NO. In addition, we think that the HOF of 2-HO2C–c-C5H4NO is much larger than that of 3-HO2C–c-C5H4NO and 4-HO2C–c-C5H4NO, which may be the result of intramolecular hydrogen bond formation and further measurements are needed to reexamine the HOFs for 2-HO2C–c-C5H4NO, 3-HO2C–c-C5H4NO, and 4-HO2C–c-C5H4NO.

NNO2 bond dissociation energies in acetonitrile: An assessment of contemporary computational methods

The assessment of the N-NO2 bond dissociation energies (BDEs) was performed by various calculating methods (B3LYP, B3PW91, B3P86, B1LYP, BMK, MPWB1K, PBE0, CBS-4M and M06-2X) at 6-311+G(2d,p) basis set. Compared with the experimental BDEs, the results show that BMK and B3P86 methods reproduce the experimental values well. The mean absolute deviations from the experimental values obtained by BMK and B3P86 methods were 0.5 and 1.5 kcal/mol, respectively. B3LYP, B3PW91, B1LYP, MPWB1K and PBE0 methods underestimated the homolytic N-NO2 BDEs. B3LYP, B3PW91, B1LYP, M06-2X, CBS-4M methods failed to provide an accurate description of N-NO2 BDEs for N-Nitrosulfonamide compounds and showed larger mean absolute deviations and maximum deviations. Further, substituent effect based on BMK/6-311+G(2d,p) method was analysis. Natural bond orbital analysis shows that there exist good linear correlations between E((2)) of lpN1→BD*(O1-N2) and Hammett constants and a better correlation between the BDEs and the second order stabilization energy E((2)) of lpN1→BD*(O1-N2).

Computational investigation on a series of heteroaromatic nitrogen-rich compounds

Density functional theory calculations were performed to calculate the detonation performance, frontier molecular orbitals, and impact sensitivity of a series of heteroaromatic nitro-rich compounds. The results show that all the title compounds exhibit high-positive solid-phase heats of formation. The detonation velocities and pressures of the title compounds were predicted via the Kamlet–Jacobs equation. Thirteen compounds have larger D and P than HMX because of the big crystal densities and solid HOFs. The analysis of frontier molecular orbitals shows that two compounds may be kinetically more stable and chemically less active than other compounds. In addition, most of the compounds were found to have lower impact sensitivity than HMX.