Bond dissociation energies for removal of nitrogen dioxide groups in 10 aliphatic nitro compounds, including nitromethane, nitroethylene, nitroethane, dinitromethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane, 2-m...Bond dissociation energies for removal of nitrogen dioxide groups in 10 aliphatic nitro compounds, including nitromethane, nitroethylene, nitroethane, dinitromethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane, 2-methyl-2-nitropropane, nitropentane, and nitrohexane, are calculated using the highly accurate complete basis set （CBS-Q） and the three hybrid density functional theory （DFT） methods B3LYP, B3PW91 and B3P86 with 6-31G^＊＊ basis set. By comparing the computed bond dissociation energies and experimental results, we find that the B3LYP/6-31G^＊＊ and B3PW91/6-31G^＊＊ methods are incapable of predicting the satisfactory bond dissociation energy （BDE）. However, B3P86/6-31G^＊＊ and CBS-Q computations are capable of giving the calculated BDEs, which are in extraordinary agreement with the experimental data. Nevertheless, since CBS-Q computational demands increase rapidly with the number of containing atoms in molecules, larger molecules soon become prohibitively expensive. Therefore, we suggest to take the B3P86/6-31G^＊＊ method as a reliable method of computing the BDEs for removal of the NO2 groups in the aliphatic nitro compounds.展开更多
As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III,and then to phase V with increasing pressure at 300 K have been widely confirmed. However, ther...As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III,and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction(XRD) technology. Using x-ray absorption fine structure(XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.展开更多
It is unclear whether there is a liquid-liquid phase transition or not in the bismuth melt at high temperature and high pressure.If so,it will be necessary to confirm the boundary of the liquid-liquid phase transition...It is unclear whether there is a liquid-liquid phase transition or not in the bismuth melt at high temperature and high pressure.If so,it will be necessary to confirm the boundary of the liquid-liquid phase transition and clarify whether it is a first-order phase transition.Here,based on x-ray absorption spectra and simulations,the temperature dependence of bismuth structures is investigated under different pressures.According to the similarity of characteristic peaks of xray absorption near edge structure(XANES)spectra,we estimate the possible temperature ranges of liquid-liquid phase transition to be 779-799 K at 2.74 GPa and 859-879 K at 2.78 GPa,809-819 K at 3.38 GPa and 829-839 K at 3.39 GPa and 729-739 K at 4.78 GPa.Using ab initio molecular dynamics(AIMD)simulations,we obtain the stable structures of the bismuth melt at different temperatures and pressures,and calculated their electronic structures.Meanwhile,two stable phases(phaseⅢ-like and phase IV-like)of bismuth melts are obtained from different initial phases of bismuth solids(phaseⅢand phase IV)under the same condition(3.20 GPa and 800 K).Assuming that the bismuth melt undergoes a phase transition from IV-like toⅢ-like between 809 K and 819 K at 3.38 GPa,the calculated electronic structures are consistent with the XANES spectra,which provides a possible explanation for the first-order liquid-liquid phase transition.展开更多
基金Supported by the National Natural Science Foundation of China under grant Nos 10376021, 10274055, the Chinese Academy of Engineering Physics, and the Research Fund for the Doctoral Programme of High Education of China under grant No 20020610001.
文摘Bond dissociation energies for removal of nitrogen dioxide groups in 10 aliphatic nitro compounds, including nitromethane, nitroethylene, nitroethane, dinitromethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane, 2-methyl-2-nitropropane, nitropentane, and nitrohexane, are calculated using the highly accurate complete basis set （CBS-Q） and the three hybrid density functional theory （DFT） methods B3LYP, B3PW91 and B3P86 with 6-31G^＊＊ basis set. By comparing the computed bond dissociation energies and experimental results, we find that the B3LYP/6-31G^＊＊ and B3PW91/6-31G^＊＊ methods are incapable of predicting the satisfactory bond dissociation energy （BDE）. However, B3P86/6-31G^＊＊ and CBS-Q computations are capable of giving the calculated BDEs, which are in extraordinary agreement with the experimental data. Nevertheless, since CBS-Q computational demands increase rapidly with the number of containing atoms in molecules, larger molecules soon become prohibitively expensive. Therefore, we suggest to take the B3P86/6-31G^＊＊ method as a reliable method of computing the BDEs for removal of the NO2 groups in the aliphatic nitro compounds.
基金supported by the National Natural Science Foundation of China(Grant Nos.10904133,11304294,11274281,11404006,and U1230201)the Development Foundation of China Academy of Engineering Physics(Grant Nos.2015B0101004,2013B0401062,and 2012A0101001)the Research Foundation of the Laboratory of Shock Wave and Detonation,China(Grant No.9140C670201140C67282)
文摘As a widely used pressure calibrator, the structural phase transitions of bismuth from phase I, to phase II, to phase III,and then to phase V with increasing pressure at 300 K have been widely confirmed. However, there are different structural versions for phase III, most of which are determined by x-ray diffraction(XRD) technology. Using x-ray absorption fine structure(XAFS) measurements combined with ab initio calculations, we show that the proposed incommensurate composite structure of bismuth of the three configurations is the best option. An abnormal continuous increase of the nearest-neighbor distance of phase III with elevated pressure is also observed. The electronic structure transformation from semimetal to metal is responsible for the complex behavior of structure transformation.
基金supported by the CAEP Foundation(Grant No.CX2019002)the Science Challenge Project(Grant No.TZ2016001)the National Natural Science Foundation of China(Grant Nos.11602251,U1730248,and11802290)。
文摘It is unclear whether there is a liquid-liquid phase transition or not in the bismuth melt at high temperature and high pressure.If so,it will be necessary to confirm the boundary of the liquid-liquid phase transition and clarify whether it is a first-order phase transition.Here,based on x-ray absorption spectra and simulations,the temperature dependence of bismuth structures is investigated under different pressures.According to the similarity of characteristic peaks of xray absorption near edge structure(XANES)spectra,we estimate the possible temperature ranges of liquid-liquid phase transition to be 779-799 K at 2.74 GPa and 859-879 K at 2.78 GPa,809-819 K at 3.38 GPa and 829-839 K at 3.39 GPa and 729-739 K at 4.78 GPa.Using ab initio molecular dynamics(AIMD)simulations,we obtain the stable structures of the bismuth melt at different temperatures and pressures,and calculated their electronic structures.Meanwhile,two stable phases(phaseⅢ-like and phase IV-like)of bismuth melts are obtained from different initial phases of bismuth solids(phaseⅢand phase IV)under the same condition(3.20 GPa and 800 K).Assuming that the bismuth melt undergoes a phase transition from IV-like toⅢ-like between 809 K and 819 K at 3.38 GPa,the calculated electronic structures are consistent with the XANES spectra,which provides a possible explanation for the first-order liquid-liquid phase transition.
