Calculation of the bonding energy of a molecular orbital for a series of small molecules has been carried out by using ab initio STO-3G method. The results obtained demonstrate that the concept of the molecular orbita...Calculation of the bonding energy of a molecular orbital for a series of small molecules has been carried out by using ab initio STO-3G method. The results obtained demonstrate that the concept of the molecular orbital bonding energy is applicable for judging whether a molecular orbital is bonding, nonbonding or antibonding besides Mulliken overlap criterion.展开更多
Neutral aluminium alkyls are well known to act as ethylene oligomerization and polymerization catalysts and cocatalysts.On the basis of the full optimization of alkylaluminium compounds with Gaussian 98 program packag...Neutral aluminium alkyls are well known to act as ethylene oligomerization and polymerization catalysts and cocatalysts.On the basis of the full optimization of alkylaluminium compounds with Gaussian 98 program package at the B3LYP/6-31G** level,the selected structures and bonding energies were investigated extensively.The geometries and bonding energies of AlR3(R = H,CH3,C2H5,C3H7,C4H9) and Al(C2H5)2R'(R' = C2H5,C3H7,C4H9,C5H11,C6H13) were investigated extensively,and we found that,along with the prolongation of carbon chains the terminal C-C bond is shortened gradually until to a constant value of about 0.1532 nm in C4H9;and the bonding energy almost remains constant.The dative bonding of C2H4 to Al(C2H5)3,whose bonding energy is only 15.30 kJ/mol,is very weak.展开更多
Semiempirical quantum chemical method AM1 was employed to calculate the highest occupied molecular orbital (HOMO) energy levels (E-HOMO) for various types of antioxidants. It was verified that the correlation between ...Semiempirical quantum chemical method AM1 was employed to calculate the highest occupied molecular orbital (HOMO) energy levels (E-HOMO) for various types of antioxidants. It was verified that the correlation between logarithm of free radical scavenging rate constants (1gks) and E-HOMO substantially arises from the correlation between E-HOMO and O-H bond dissociation energies (BDE) of antioxidants. Furthermore, E-HOMO were poorly correlated with the logarithm of relative free radical scavenging rate constants (1gk(3)/k(1)) for various types of antioxidants that possess complex structures (r = 0.5602). So in a broad sense, E-HOMO was not an appropriate parameter to characterize the free radical scavenging activity of antioxidants.展开更多
Some highly designable protein structures have dented on the surface of their native structures, and are not full compactly folded. According to hydrophobic-polar (HP) model the most designable structures are full c...Some highly designable protein structures have dented on the surface of their native structures, and are not full compactly folded. According to hydrophobic-polar (HP) model the most designable structures are full compactly folded. To investigate the designability of the dented structures, we introduce the hydrogen bond energy in the secondary structures by using the secondary-structure-favored HP model proposed by Ou-yang etc. The result shows that the average designability increases with the strength of the hydrogen bond. The designabilities of the structures with same dented shape increase exponentially with the number of secondary structure sites. The dented structures can have the highest designabilities for a certain value of hydrogen bond energy density.展开更多
hethesisanalysesthevalenceelectronstructuresof phase Γin Fe Zn transitionallayerof heat galvanized sheet used in cars by applying the Empirical Electron Theory of Solids andMolecules, and calculatesthebond energy o...hethesisanalysesthevalenceelectronstructuresof phase Γin Fe Zn transitionallayerof heat galvanized sheet used in cars by applying the Empirical Electron Theory of Solids andMolecules, and calculatesthebond energy ofthe major bondsand cohesiveenergy ofcrystals,from which we draw theconclusion:sincecrystal has alargercohesiveenergy, it has higherhardness, butsinceitsbondenergyisratherlow ,itiseasytobreak under pressurefrom out side, and thecrackiseasytocome up andspreadin phase Γ.展开更多
Based on the empirical electron surface model (EESM),the covalent electron density of dangling bonds (CEDDB) was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculat...Based on the empirical electron surface model (EESM),the covalent electron density of dangling bonds (CEDDB) was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculation results show that CEDDB has a great influence on the surface energy of various index surfaces and the anisotropy of the surface.The calculated surface energy is in agreement with experimental and other theoretical values.The calculated surface energy of the close-packed (111) surface has the lowest surface energy,which agrees with the theoretical prediction.Also,it is found that the spatial distribution of covalent bonds has a great influence on the surface energy of various index surfaces.Therefore,CEDDB should be a suitable parameter to describe and quantify the dangling bonds and surface energy of various crystal surfaces.展开更多
Polybrominated diphenyl ethers(PBDEs)are a kind of serious pollutants in the ocean.Biodegradation is considered as an economical and safe way for PBDEs removal and reductive debromination dominates the initial pathway...Polybrominated diphenyl ethers(PBDEs)are a kind of serious pollutants in the ocean.Biodegradation is considered as an economical and safe way for PBDEs removal and reductive debromination dominates the initial pathway of anaerobic degradation.On the basis of experimental study,Octa-BDE 197,Hepta-BDE 183,Hexa-BDE 153,Penta-BDE 99 and Tetra-BDE 47 were selected as the initial degradation objects,and their debromination degradation were studied using density functional theory.The structures were optimized by Gaussian 09 program.Furthermore,the molecular orbitals and charge distribution were analyzed.All C-Br bond dissociation energies at different positions including ortho,meta and para bromine atoms were calculated and the sequence of debromination was obtained.There is a close relationship between molecular structure,charge,molecular orbital and C-Br bond.All PBDEs exhibited similar debromination pathways with preferential removal of meta and para bromines.展开更多
Geometric and electronic properties of Pdn–1Pb and Pdn (n≤8) clusters have been studied by using density functional theory with effective core potentials, focusing on the differences between mono- and bimetallic c...Geometric and electronic properties of Pdn–1Pb and Pdn (n≤8) clusters have been studied by using density functional theory with effective core potentials, focusing on the differences between mono- and bimetallic clusters. The average bond length of Pdn–1Pb (n≤8) bimetallic clusters is longer than that of pure palladium clusters except for n = 2 and 3. The most stable structure of Pdn–1Pb (n≤7) is the singlet where there is at least a Pd or Pb atom on its excited state. The energy gaps of Pd–Pb binary clusters are narrower than those of Pdn clusters, and then the chemical activity is strengthened when Pdn clusters are doped with Pb.展开更多
The stability of C36H2 isomers and selection rules for choosing position in addition reactions based on symmetrical C36(D6h and D2d) fullerene have been studied by means of Aihara's topological resonance energy (...The stability of C36H2 isomers and selection rules for choosing position in addition reactions based on symmetrical C36(D6h and D2d) fullerene have been studied by means of Aihara's topological resonance energy (TRE) and bond resonance energy (BRE) methods. The relation between the addition pattern and BREs is established, showing high antiaromatic bonds are preferred for addition. These results show that TRE and BRE methods can be used to predict and interpret addition sites for these systems.展开更多
C4'-H bond dissociation enthalpies of nucleosides were predicted using theoretical methods to a precision of 1-2 Kcal/mol. It was found that the stability of the C4' nucleoside radical is slightly dependent on...C4'-H bond dissociation enthalpies of nucleosides were predicted using theoretical methods to a precision of 1-2 Kcal/mol. It was found that the stability of the C4' nucleoside radical is slightly dependent on the base. The orders of stability are dA < dG < dT < dC for deoxynucleosides and U < G < A = C for nucleosides.展开更多
The adsorption process of new nicotinic derivatives on Fe(110)surface and diffusion of corrosive particles in inhibition film were studied by quantum chemistry and molecular dynamics simulation,and inhibition mechanis...The adsorption process of new nicotinic derivatives on Fe(110)surface and diffusion of corrosive particles in inhibition film were studied by quantum chemistry and molecular dynamics simulation,and inhibition mechanism of inhibitor was discussed.The results indicated that the main active sites of three inhibitors are located in N atoms on the five membered ring.The inhibitor YM-1 has the strongest activity of electrophilic reaction,and the adsorption process of inhibitor molecules is polycentric chemisorption.The adsorption energy for inhibitors followed the order of YM-1>YM-2>YM-3.The adsorption film YM-1 more effectively impedes the diffusion and migration of the corrosive particles,and also has the best inhibitory effect on Cl-.In addition,the bond energy of chemical bond formed between inhibitor and Fe atom increases as the increase of temperature.The interaction between corrosive particles and inhibitors is dominated by Van der Waals force.展开更多
By using the density functional theory (B3LYP) and four highly accurate complete basis set (CBS-Q, CBS-QB3, CBS-Lq, and CBS-4M)ab initio methods, the X(C, N, O)-NO2 bond dissociation energies (BDEs) for CH3NO2...By using the density functional theory (B3LYP) and four highly accurate complete basis set (CBS-Q, CBS-QB3, CBS-Lq, and CBS-4M)ab initio methods, the X(C, N, O)-NO2 bond dissociation energies (BDEs) for CH3NO2, C2H3NO2, C2H5NO2, HONO2, CH3ONO2, C2H5ONO2, NH2NO2 (CH3)2NNO2 are computed. By comparing the computed BDEs and experimental results, it is found that the B3LYP method is unable to predict satisfactorily the results of bond dissociation energy (BDE); however, all four CBS models are generally able to give reliable predication of the X(C, N, O)-NO2 BDEs for these nitro compounds. Moreover, the CBS-4M calculation is the least computationally demanding among the four CBS methods considered, Therefore, we recommend CBS-4M method as a reliable method of computing the BDEs for this nitro compound system.展开更多
The molecular structures and the vibrational frequencies of uranium hexahalides UX6 (X=F, Cl, Br and I) molecules are investigated by using local density approximation (LDA) and generalised gradient approximation ...The molecular structures and the vibrational frequencies of uranium hexahalides UX6 (X=F, Cl, Br and I) molecules are investigated by using local density approximation (LDA) and generalised gradient approximation (GGA) functions (BP, BLYP and RPBE) in combination with two different relativistic methods (scalar and scalar+spin-orbit relativistic effects). The calculated results show that the differences are trivial between scalar and scalar+spin-orbit relativistic methods. The vibrational frequencies are also compared with existing experimental values, and overall, the RPBE approach gives the smallest error. The bond dissociation energies (BDEs) of UX6 are computed by using the RPBE function, thereby obtaining exact vibrational frequencies. In addition, the calculated magnitudes of the spin orbit effect on the BDE of UX6 (X=F, Cl, Br, and I) are found to be approximately -0.3198, 0.3218, -0.3609 and -0.4415 eV, respectively.展开更多
Quantum chemical calculations are performed to investigate the equilibrium C-COOH bond distances and the bond dissociation energies(BDEs) for 15 acids.These compounds are studied by utilizing the hybrid density func...Quantum chemical calculations are performed to investigate the equilibrium C-COOH bond distances and the bond dissociation energies(BDEs) for 15 acids.These compounds are studied by utilizing the hybrid density functional theory(DFT)(B3LYP,B3PW91,B3P86,PBE1PBE) and the complete basis set(CBS-Q) method in conjunction with the 6311G^** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work.Comparisons between the computational results and the experimental values reveal that CBS-Q method,which can produce reasonable BDEs for some systems in our previous work,seems unable to predict accurate BDEs here.However,the B3P86 calculated results accord very well with the experimental values,within an average absolute error of 2.3 kcal/mol.Thus,B3P86 method is suitable for computing the reliable BDEs of C-COOH bond for carboxylic acid compounds.In addition,the energy gaps between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of studied compounds are estimated,based on which the relative thermal stabilities of the studied acids are also discussed.展开更多
Relationships between the structure characteristics of natural p-terphenyl com- pounds isolated from three edible mushrooms (Thelephora ganbajun, Thelephora aeronautical, and Boletopsis grisea) indigenous to China a...Relationships between the structure characteristics of natural p-terphenyl com- pounds isolated from three edible mushrooms (Thelephora ganbajun, Thelephora aeronautical, and Boletopsis grisea) indigenous to China and their mechanism of antioxidant activity were studied. Geometry structures of terphenyl molecule and four corresponding radicals, bond dissociation energy (BDE), frontier orbitals (HOMO and LUMO) and single electron density were calculated using DFT methods (B3LYP/6-311G**). The computational results which are consistent with the experimental data well show that terphenyl molecule scavenges DPPH radical by hydrogen abstract mechanism and the high antioxidant activity depends on the substitution position of hydroxyls. Two active 7-, 8-hydroxyls facilitate the hydrogen abstraction due to the intramolecular hydrogen bond and the resonance effect makes 4-hydroxyl radical more stable.展开更多
Bond dissociation energies for the removal of nitrogen dioxide group in some nitroalkane energetic materials have been calculated by using the three hybrid density functional theory (DFT) methods B3LYP, B3PW91 and B...Bond dissociation energies for the removal of nitrogen dioxide group in some nitroalkane energetic materials have been calculated by using the three hybrid density functional theory (DFT) methods B3LYP, B3PW91 and B3P86 with 6-31g^** and 6-311g^** basis sets. The computed BDEs have been compared with the available experimental results. It is found that the B3P86 method with 6-31g^** and 6-311g^** basis sets can obtain satisfactory bond dissociation energies (BDEs), which are in extraordinary agreement with the experimental data. Considering the smaller mean absolute deviation and maximum difference, the reliable B3P86/6-311g^** method was recommended to compute the BDEs for the removal of nitrogen dioxide group in the nitroalkane energetic materials. Using the method, the BDEs of 8 other nitroalkane energetic materials have been calculated and the maximum difference from experimental value is 1.76 kcal.mo1^-1 (for the BDE of tC4Hg-NOz), which further proves the reliability of B3P86/6-311g^** method. In addition, it is noted that the BDEs of C-NO2 bond change slightly for main chain nitroalkane compounds with the maximum difference of only 3.43 kcal mo1^-1.展开更多
The N-NO2 bond dissociation energies (BDEs) for 7 energetic materials were computed by means of accurate density functional theory (B3LYP, B3PW91 and B3P86) with 6-31G** and 6-311G** basis sets. By comparing t...The N-NO2 bond dissociation energies (BDEs) for 7 energetic materials were computed by means of accurate density functional theory (B3LYP, B3PW91 and B3P86) with 6-31G** and 6-311G** basis sets. By comparing the computed energies and experimental results, we find that the B3P86/6-311G** method can give good results of BDE, which has the mean absolute deviation of 1.30kcal/mol. In addition, substituent effects were also taken into account. It is noted that the Hammett constants of substituent groups are related to the BDEs of the N-NO2 bond and the bond dissociation energies of the energetic materials studied decrease when increasing the number of NO2 group.展开更多
Clusters greatly influence thermophysical properties of near critical gases. The cluster structures of supercritical fluids in general and Carbon Dioxide especially are important for the advanced supercritical fluid t...Clusters greatly influence thermophysical properties of near critical gases. The cluster structures of supercritical fluids in general and Carbon Dioxide especially are important for the advanced supercritical fluid technologies and analytics development. The paper extends to near critical densities the developed earlier methods to extract the clusters’ properties from Online Electronic Database of NIST on thermophysical properties of fluids. This Database contains a hidden knowledge of cluster fractions’ properties in real gases. The discovered earlier linear chain clusters dominate at intermediate densities. Their properties can be extrapolated to high density gases, thus opening the way to study large 3D clusters in near critical zone. The potential energy density of a gas, cleared from the chain clusters’ contribution, reflects only the 3D clusters’ characteristics. A series expansion of this value by the Monomer Fraction density discovers properties of n-particle 3D clusters. The paper demonstrates a discrete row of 3D clusters’ particle numbers and gives estimations for bond energies of these clusters.展开更多
To study the extraction difficulty of lithium ions from various crystal planes of Li2 TiO3, according to the first principle, four representative crystal surfaces of Li2TiO3(precursor),(-133),(-206),(002) and...To study the extraction difficulty of lithium ions from various crystal planes of Li2 TiO3, according to the first principle, four representative crystal surfaces of Li2TiO3(precursor),(-133),(-206),(002) and(-131), were selected to establish a model and to calculate the surface energy, bond length and population using Materials Studio 5.5(MS 5.5). The results demonstrate that there is no direct relationship between the surface energy and the order of disappearance of the four diffraction peaks when lithium titanate is treated with hydrochloric acid, instead, the difficulty of Li~+ extraction from various crystal faces corresponds to the Li-O bond strength. Lithium ion is easy to remove from(-133) and(-206) due to the relatively weak Li-O bond strength. In contrast, Li+ extraction requires a longer time for(002) and(-131).展开更多
文摘Calculation of the bonding energy of a molecular orbital for a series of small molecules has been carried out by using ab initio STO-3G method. The results obtained demonstrate that the concept of the molecular orbital bonding energy is applicable for judging whether a molecular orbital is bonding, nonbonding or antibonding besides Mulliken overlap criterion.
基金supported by the National Natural Science Foundation of China (No. 10674099)
文摘Neutral aluminium alkyls are well known to act as ethylene oligomerization and polymerization catalysts and cocatalysts.On the basis of the full optimization of alkylaluminium compounds with Gaussian 98 program package at the B3LYP/6-31G** level,the selected structures and bonding energies were investigated extensively.The geometries and bonding energies of AlR3(R = H,CH3,C2H5,C3H7,C4H9) and Al(C2H5)2R'(R' = C2H5,C3H7,C4H9,C5H11,C6H13) were investigated extensively,and we found that,along with the prolongation of carbon chains the terminal C-C bond is shortened gradually until to a constant value of about 0.1532 nm in C4H9;and the bonding energy almost remains constant.The dative bonding of C2H4 to Al(C2H5)3,whose bonding energy is only 15.30 kJ/mol,is very weak.
文摘Semiempirical quantum chemical method AM1 was employed to calculate the highest occupied molecular orbital (HOMO) energy levels (E-HOMO) for various types of antioxidants. It was verified that the correlation between logarithm of free radical scavenging rate constants (1gks) and E-HOMO substantially arises from the correlation between E-HOMO and O-H bond dissociation energies (BDE) of antioxidants. Furthermore, E-HOMO were poorly correlated with the logarithm of relative free radical scavenging rate constants (1gk(3)/k(1)) for various types of antioxidants that possess complex structures (r = 0.5602). So in a broad sense, E-HOMO was not an appropriate parameter to characterize the free radical scavenging activity of antioxidants.
基金Supported by the Foundation for the Author of National Excellent Doctoral Dissertation of China (200525)the Science and Tech-nology Program of Wuhan City (20067003111-07)
文摘Some highly designable protein structures have dented on the surface of their native structures, and are not full compactly folded. According to hydrophobic-polar (HP) model the most designable structures are full compactly folded. To investigate the designability of the dented structures, we introduce the hydrogen bond energy in the secondary structures by using the secondary-structure-favored HP model proposed by Ou-yang etc. The result shows that the average designability increases with the strength of the hydrogen bond. The designabilities of the structures with same dented shape increase exponentially with the number of secondary structure sites. The dented structures can have the highest designabilities for a certain value of hydrogen bond energy density.
文摘hethesisanalysesthevalenceelectronstructuresof phase Γin Fe Zn transitionallayerof heat galvanized sheet used in cars by applying the Empirical Electron Theory of Solids andMolecules, and calculatesthebond energy ofthe major bondsand cohesiveenergy ofcrystals,from which we draw theconclusion:sincecrystal has alargercohesiveenergy, it has higherhardness, butsinceitsbondenergyisratherlow ,itiseasytobreak under pressurefrom out side, and thecrackiseasytocome up andspreadin phase Γ.
基金supported by the Beijing Natural Science Foundation,China (No.2072014)the Ph.D. Program Foundation of the Ministry of Education of China (No.200800100006)
文摘Based on the empirical electron surface model (EESM),the covalent electron density of dangling bonds (CEDDB) was calculated for various crystal planes of gold,and the surface energy was calculated further.Calculation results show that CEDDB has a great influence on the surface energy of various index surfaces and the anisotropy of the surface.The calculated surface energy is in agreement with experimental and other theoretical values.The calculated surface energy of the close-packed (111) surface has the lowest surface energy,which agrees with the theoretical prediction.Also,it is found that the spatial distribution of covalent bonds has a great influence on the surface energy of various index surfaces.Therefore,CEDDB should be a suitable parameter to describe and quantify the dangling bonds and surface energy of various crystal surfaces.
基金the National Natural Science Foundation of China(Nos.41406090,42176045)the Science Foundation of Qingdao Agricultural University(No.631302)+1 种基金the Fujian Key Laboratory of Functional Marine Sensing Materials,Minjiang University(No.MJUKF-FMSM202102)the Natural Science Foundation of Shandong Province(Nos.ZR2019 MB020,ZR2020MB119)。
文摘Polybrominated diphenyl ethers(PBDEs)are a kind of serious pollutants in the ocean.Biodegradation is considered as an economical and safe way for PBDEs removal and reductive debromination dominates the initial pathway of anaerobic degradation.On the basis of experimental study,Octa-BDE 197,Hepta-BDE 183,Hexa-BDE 153,Penta-BDE 99 and Tetra-BDE 47 were selected as the initial degradation objects,and their debromination degradation were studied using density functional theory.The structures were optimized by Gaussian 09 program.Furthermore,the molecular orbitals and charge distribution were analyzed.All C-Br bond dissociation energies at different positions including ortho,meta and para bromine atoms were calculated and the sequence of debromination was obtained.There is a close relationship between molecular structure,charge,molecular orbital and C-Br bond.All PBDEs exhibited similar debromination pathways with preferential removal of meta and para bromines.
文摘Geometric and electronic properties of Pdn–1Pb and Pdn (n≤8) clusters have been studied by using density functional theory with effective core potentials, focusing on the differences between mono- and bimetallic clusters. The average bond length of Pdn–1Pb (n≤8) bimetallic clusters is longer than that of pure palladium clusters except for n = 2 and 3. The most stable structure of Pdn–1Pb (n≤7) is the singlet where there is at least a Pd or Pb atom on its excited state. The energy gaps of Pd–Pb binary clusters are narrower than those of Pdn clusters, and then the chemical activity is strengthened when Pdn clusters are doped with Pb.
基金The project was sponsored by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (No. [2005]383)
文摘The stability of C36H2 isomers and selection rules for choosing position in addition reactions based on symmetrical C36(D6h and D2d) fullerene have been studied by means of Aihara's topological resonance energy (TRE) and bond resonance energy (BRE) methods. The relation between the addition pattern and BREs is established, showing high antiaromatic bonds are preferred for addition. These results show that TRE and BRE methods can be used to predict and interpret addition sites for these systems.
基金NNSFC(No.20272057)the State Ministry of Education for the financial support.
文摘C4'-H bond dissociation enthalpies of nucleosides were predicted using theoretical methods to a precision of 1-2 Kcal/mol. It was found that the stability of the C4' nucleoside radical is slightly dependent on the base. The orders of stability are dA < dG < dT < dC for deoxynucleosides and U < G < A = C for nucleosides.
基金supported by the National Key R&D Program of China under Grant[No.2017YFC0805800-02].
文摘The adsorption process of new nicotinic derivatives on Fe(110)surface and diffusion of corrosive particles in inhibition film were studied by quantum chemistry and molecular dynamics simulation,and inhibition mechanism of inhibitor was discussed.The results indicated that the main active sites of three inhibitors are located in N atoms on the five membered ring.The inhibitor YM-1 has the strongest activity of electrophilic reaction,and the adsorption process of inhibitor molecules is polycentric chemisorption.The adsorption energy for inhibitors followed the order of YM-1>YM-2>YM-3.The adsorption film YM-1 more effectively impedes the diffusion and migration of the corrosive particles,and also has the best inhibitory effect on Cl-.In addition,the bond energy of chemical bond formed between inhibitor and Fe atom increases as the increase of temperature.The interaction between corrosive particles and inhibitors is dominated by Van der Waals force.
基金Project supported by the National Natural Science Foundation of China and China Academy of Engineering Physics (Grant Nos 10376021, 10274055).
文摘By using the density functional theory (B3LYP) and four highly accurate complete basis set (CBS-Q, CBS-QB3, CBS-Lq, and CBS-4M)ab initio methods, the X(C, N, O)-NO2 bond dissociation energies (BDEs) for CH3NO2, C2H3NO2, C2H5NO2, HONO2, CH3ONO2, C2H5ONO2, NH2NO2 (CH3)2NNO2 are computed. By comparing the computed BDEs and experimental results, it is found that the B3LYP method is unable to predict satisfactorily the results of bond dissociation energy (BDE); however, all four CBS models are generally able to give reliable predication of the X(C, N, O)-NO2 BDEs for these nitro compounds. Moreover, the CBS-4M calculation is the least computationally demanding among the four CBS methods considered, Therefore, we recommend CBS-4M method as a reliable method of computing the BDEs for this nitro compound system.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60278020)
文摘The molecular structures and the vibrational frequencies of uranium hexahalides UX6 (X=F, Cl, Br and I) molecules are investigated by using local density approximation (LDA) and generalised gradient approximation (GGA) functions (BP, BLYP and RPBE) in combination with two different relativistic methods (scalar and scalar+spin-orbit relativistic effects). The calculated results show that the differences are trivial between scalar and scalar+spin-orbit relativistic methods. The vibrational frequencies are also compared with existing experimental values, and overall, the RPBE approach gives the smallest error. The bond dissociation energies (BDEs) of UX6 are computed by using the RPBE function, thereby obtaining exact vibrational frequencies. In addition, the calculated magnitudes of the spin orbit effect on the BDE of UX6 (X=F, Cl, Br, and I) are found to be approximately -0.3198, 0.3218, -0.3609 and -0.4415 eV, respectively.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11047176)the Research Foundation of Education Bureau of Hubei Province,China (Grant Nos. Q20111305,B20101303,T201204,B20111304,and Q20091215)
文摘Quantum chemical calculations are performed to investigate the equilibrium C-COOH bond distances and the bond dissociation energies(BDEs) for 15 acids.These compounds are studied by utilizing the hybrid density functional theory(DFT)(B3LYP,B3PW91,B3P86,PBE1PBE) and the complete basis set(CBS-Q) method in conjunction with the 6311G^** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work.Comparisons between the computational results and the experimental values reveal that CBS-Q method,which can produce reasonable BDEs for some systems in our previous work,seems unable to predict accurate BDEs here.However,the B3P86 calculated results accord very well with the experimental values,within an average absolute error of 2.3 kcal/mol.Thus,B3P86 method is suitable for computing the reliable BDEs of C-COOH bond for carboxylic acid compounds.In addition,the energy gaps between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of studied compounds are estimated,based on which the relative thermal stabilities of the studied acids are also discussed.
基金Supported by NNSFC(10901135,11171293)Natural Science Foundation of Yunnan Province(2008CD081,2010CC003)+1 种基金Educational Commission of Yunnan Province(2011Y296)Foundation of Honghe University(2010PY0104,10XJY113)
文摘Relationships between the structure characteristics of natural p-terphenyl com- pounds isolated from three edible mushrooms (Thelephora ganbajun, Thelephora aeronautical, and Boletopsis grisea) indigenous to China and their mechanism of antioxidant activity were studied. Geometry structures of terphenyl molecule and four corresponding radicals, bond dissociation energy (BDE), frontier orbitals (HOMO and LUMO) and single electron density were calculated using DFT methods (B3LYP/6-311G**). The computational results which are consistent with the experimental data well show that terphenyl molecule scavenges DPPH radical by hydrogen abstract mechanism and the high antioxidant activity depends on the substitution position of hydroxyls. Two active 7-, 8-hydroxyls facilitate the hydrogen abstraction due to the intramolecular hydrogen bond and the resonance effect makes 4-hydroxyl radical more stable.
基金The project was supported by the National Natural Science Foundation of China (No. 10574096 and 10676025)
文摘Bond dissociation energies for the removal of nitrogen dioxide group in some nitroalkane energetic materials have been calculated by using the three hybrid density functional theory (DFT) methods B3LYP, B3PW91 and B3P86 with 6-31g^** and 6-311g^** basis sets. The computed BDEs have been compared with the available experimental results. It is found that the B3P86 method with 6-31g^** and 6-311g^** basis sets can obtain satisfactory bond dissociation energies (BDEs), which are in extraordinary agreement with the experimental data. Considering the smaller mean absolute deviation and maximum difference, the reliable B3P86/6-311g^** method was recommended to compute the BDEs for the removal of nitrogen dioxide group in the nitroalkane energetic materials. Using the method, the BDEs of 8 other nitroalkane energetic materials have been calculated and the maximum difference from experimental value is 1.76 kcal.mo1^-1 (for the BDE of tC4Hg-NOz), which further proves the reliability of B3P86/6-311g^** method. In addition, it is noted that the BDEs of C-NO2 bond change slightly for main chain nitroalkane compounds with the maximum difference of only 3.43 kcal mo1^-1.
基金The project was supported by the National Natural Science Foundation of China (No. 10774039)
文摘The N-NO2 bond dissociation energies (BDEs) for 7 energetic materials were computed by means of accurate density functional theory (B3LYP, B3PW91 and B3P86) with 6-31G** and 6-311G** basis sets. By comparing the computed energies and experimental results, we find that the B3P86/6-311G** method can give good results of BDE, which has the mean absolute deviation of 1.30kcal/mol. In addition, substituent effects were also taken into account. It is noted that the Hammett constants of substituent groups are related to the BDEs of the N-NO2 bond and the bond dissociation energies of the energetic materials studied decrease when increasing the number of NO2 group.
文摘Clusters greatly influence thermophysical properties of near critical gases. The cluster structures of supercritical fluids in general and Carbon Dioxide especially are important for the advanced supercritical fluid technologies and analytics development. The paper extends to near critical densities the developed earlier methods to extract the clusters’ properties from Online Electronic Database of NIST on thermophysical properties of fluids. This Database contains a hidden knowledge of cluster fractions’ properties in real gases. The discovered earlier linear chain clusters dominate at intermediate densities. Their properties can be extrapolated to high density gases, thus opening the way to study large 3D clusters in near critical zone. The potential energy density of a gas, cleared from the chain clusters’ contribution, reflects only the 3D clusters’ characteristics. A series expansion of this value by the Monomer Fraction density discovers properties of n-particle 3D clusters. The paper demonstrates a discrete row of 3D clusters’ particle numbers and gives estimations for bond energies of these clusters.
基金Funded partly by the Key Project of Natural Science of Sichuan Provincial Education Department(No.16ZA0309)the Doctoral Research Start-up Funding(No.15B16)
文摘To study the extraction difficulty of lithium ions from various crystal planes of Li2 TiO3, according to the first principle, four representative crystal surfaces of Li2TiO3(precursor),(-133),(-206),(002) and(-131), were selected to establish a model and to calculate the surface energy, bond length and population using Materials Studio 5.5(MS 5.5). The results demonstrate that there is no direct relationship between the surface energy and the order of disappearance of the four diffraction peaks when lithium titanate is treated with hydrochloric acid, instead, the difficulty of Li~+ extraction from various crystal faces corresponds to the Li-O bond strength. Lithium ion is easy to remove from(-133) and(-206) due to the relatively weak Li-O bond strength. In contrast, Li+ extraction requires a longer time for(002) and(-131).