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
First-principles calculations based on the density-functional theory were employed to study the crystal structure of vanadium phosphide compounds,such as V3P,V2P,VP,VP2 and VP4. Cohesive energy of five types of vanadi...First-principles calculations based on the density-functional theory were employed to study the crystal structure of vanadium phosphide compounds,such as V3P,V2P,VP,VP2 and VP4. Cohesive energy of five types of vanadium phosphide compounds was calculated to assess their structural stability. The charge density distribution and densities of states of vanadium phosphides were discussed to study further their electronic structures. The results show that the structure of metal-rich compounds is considerably more stable than the phosphorus-rich compositions,and covalent bond exists between the V and P atoms of V3P,V2P,VP,VP2 and VP4.展开更多
This paper uses a molecular static approach with a many-body potential to investigate the surface energetic and bonding characteristics of tetrahexahedral platinum nanocrystals enclosed by high-index facets such as {2...This paper uses a molecular static approach with a many-body potential to investigate the surface energetic and bonding characteristics of tetrahexahedral platinum nanocrystals enclosed by high-index facets such as {210}, {310}, {410}, {520} and {730}. It mainly focuses on the effect of crystal size and surface Miller index on these characteristics. The results show that the surface energy and dangling bond density increase with decreasing diameter of tetrahexahedral nanocrystals and generally show an order of {210} 〉{730}〉 {520} 〉 {310} 〉 {410}. However, this order is not valid at crystal sizes below 7 nm or so. The results of corresponding surfaces are also presented for comparison.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
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 thermal analysis of precise thermophysical data for pure fluids from electronic databases is developed to investigate the molecular interaction mechanisms and parameters and the structural features of heterogeneit...The thermal analysis of precise thermophysical data for pure fluids from electronic databases is developed to investigate the molecular interaction mechanisms and parameters and the structural features of heterogeneities in fluids. The method is based on the series expansion of thermophysical values by powers of the monomer fraction density. Unlike the virial expansion by powers of the total density, the series expansion terms in this method directly reflect properties of the corresponding cluster fractions. The internal energy had been selected among thermophysical properties as the most informative for this method. The thermal analysis of its series expansion coefficients permits to estimate the temperature dependence of the pair bond parameters, the clusters’ bond energies and equilibrium constants, the structural transitions between dominating isomers of clusters. The application of method to different pure fluids, including noble and molecular gases with van der Waals and polar molecular interactions, brings unknown clusters’ characteristics for the fluids under investigation. The thermal analysis of the ordinary and heavy Water vapors points on no trivial isotopic effects. The unpredictable growth of the pair bond energy with temperature in Alkanes points on existence in hydrocarbons of some unknown molecular interaction forces in addition to dispersion forces.展开更多
Considerable interest in hydrogen bonding involving chalcogen has been growing since the IUPAC committee has redefined hydrogen bonding. Not only the focus is on unconventional acceptors, but also on donors not discus...Considerable interest in hydrogen bonding involving chalcogen has been growing since the IUPAC committee has redefined hydrogen bonding. Not only the focus is on unconventional acceptors, but also on donors not discussed before. It has been mentioned in previous studies that the proton of the H-C group could be involved in hydrogen bonding, but with conventional acceptors. In this study, we explored the ability of hydrogen bond formation of Se, S and Te acceptors with the H-C donor using Cambridge Structural Database in conjunction with Ab Initio calculations. In the CSD, there are respectively 256, 6249 and 11 R1,R2,-C=Se, R1,R2,-C=S and R1,R2,-C=Te structures that form hydrogen bonds, in which the N,N groups are majority. Except for C=S acceptor which can form a hydrogen bond with its C, C group, both C=Se and C=Te acceptors could form a hydrogen bond only with N,C and N,N groups. CSD analysis shows very similar d (norm) around -0.04 Å, while DFT-calculated interaction for N,C and N,N groups are also similar. Both interaction distances derived from CSD analysis and DFT-calculated interaction energies demonstrate that the acceptors form stable complexes with H-CF3. Besides hydrogen bonds, dispersion interactions are forces stabilizing the complexes since their contribution can reach 50%. Analysis of intra-molecular geometries and Ab Initio partial charges show that this bonding stems from resonance induced C<sup>δ+</sup>=X<sup>δ-</sup> dipoles. In many respects, both C=Se, C=S and C=Te are similar to C=S, with similar d (norm) and calculated interaction strengths.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
All-electronic relativistic density functional theory (DFT) method has been used to study the U2F6 molecule. Results from calculations predict the existence of U2F6 molecule, which has been found to be stable with a m...All-electronic relativistic density functional theory (DFT) method has been used to study the U2F6 molecule. Results from calculations predict the existence of U2F6 molecule, which has been found to be stable with a multiply bonded U2 unit. The calculations also predict that D3d symmetry of U2F6 is more stable than D3h. The optimized geometries, vibrational frequencies and infrared intensities are reported for D3d symmetry of U2F6 from Becke Three-parameter Lee-Yang-Parr (B3LYP) function with triple zeta valence plus polarization functions basis set (TZP). The bond dissociation energy (BDE) for U-U bond in the U2F6 was obtained using the same method. In addition, the entropies of U2F6 have been investigated at temperature rang from 0 to 3000K in 10 steps using the B3LYP method.展开更多
In this paper,a primary model is established for MD(molecular dynamics) simulation for the PBXs(polymer-bonded explosives) with RDX(cyclotrimethylene trinitramine) as base explosive and PS as polymer binder.A series o...In this paper,a primary model is established for MD(molecular dynamics) simulation for the PBXs(polymer-bonded explosives) with RDX(cyclotrimethylene trinitramine) as base explosive and PS as polymer binder.A series of results from the MD simulation are compared between two PBX models,which are represented by PBX1 and PBX2,respectively,including one PS molecular chain having 46 repeating units and two PS molecular chains with each having 23 repeating units.It has been found that their structural,interaction energy and mechanical properties are basically consistent between the two models.A systematic MD study for the PBX2 is performed under NPT conditions at five different temperatures,i.e.,195 K,245 K,295 K,345 K,and 395 K.We have found that with the temperature increase,the maximum bond length(L max) of RDX N N trigger bond increases,and the interaction energy(E N-N) between two N atoms of the N-N trigger bond and the cohesive energy density(CED) decrease.These phenomena agree with the experimental fact that the PBX becomes more sensitive as the temperature increases.Therefore,we propose to use the maximum bond length L max of the trigger bond of the easily decomposed and exploded component and the interaction energy E N-N of the two relevant atoms as theoretical criteria to judge or predict the relative degree of heat and impact sensitivity for the energetic composites such as PBXs and solid propellants.展开更多
Molecular dynamics (MD) method was used to simulate 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) coated with fluorine containing polymers. The mechanical properties and binding energies of PBXs were obtained. It wa...Molecular dynamics (MD) method was used to simulate 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) coated with fluorine containing polymers. The mechanical properties and binding energies of PBXs were obtained. It was found that when the number of chain monomers of fluorine containing polymers was the same, the elasticity of TATB/F2314 was increased more greatly than others and the binding energy of TATB/F2311 was the largest among four PBXs. Detonation heat and velocity of such four PBXs were calculated according to theoretical and empirical formulas. The results show that the order of detonation heat is TATB〉TATB/PVDF〉TATB/F2311〉TATB/ F2314 〉 TATB/PCTFE while the order of detonation velocity is TATB/PVDF 〈 TATB/F2311 〈 TATB/F2314 〈 TATB/PCTFE 〈TATB.展开更多
The molecular simulations of the well-known high explosive β-HMX (cyclotetramethylene tetranitramine) anditsfluorine containing polymer-bonded explosives(PBXs) were carried out with the combination method of quantum ...The molecular simulations of the well-known high explosive β-HMX (cyclotetramethylene tetranitramine) anditsfluorine containing polymer-bonded explosives(PBXs) were carried out with the combination method of quantum mechanics, molecular mechanics and molecular dynamics. The atomic cluster model, containing the β-HMX molecule and the polymer molecule whose chain dimension was about the same as β-HMX’s, was fully optimized by AM1 and PM3 semi-empirical molecular orbital and molecular mechanical methods using COMPASS and PCFF force field. Then the calculated binding energy is found to be linearly correlated to each other. Molecular dynamics simulations using COM- PASS force field were performed for β-HMX crystal and the PBXs involving β-HMX and a series of fluorine containing polymers. Their elastic coefficients, moduli and Poisson’s ratios were calculated. It is found that the mechanical prop- erties of β-HMX can be effectively improved by blending with fluorine containing polymers in small amounts.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
The energies, geometries and harmonic vibrational frequencies of 1 : 1 5-hydroxytryptamine-water (5-HT-H20) complexes are studied at the MP2/6-311 + + G(d,p) level. Natural bond orbital (NBO), quantum theory ...The energies, geometries and harmonic vibrational frequencies of 1 : 1 5-hydroxytryptamine-water (5-HT-H20) complexes are studied at the MP2/6-311 + + G(d,p) level. Natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM) analyses and the localized molecular orbital energy decomposition analysis (LMO-EDA) were performed to explore the nature of the hydrogen-bonding interactions in these complexes. Various types of hydro- gen bonds (H-bonds) are formed in these 5-HT-H20 complexes. The intermolecular C4H55HT'"Ow H-bond in HTW3 is strengthened due to the cooperativity, whereas no such cooperativity is found in the other 5-HT-H20 complexes. H-bond in which nitrogen atom of amino in 5-HT acted as proton donors was stronger than other H-bonds. Our researches show that the hydrogen bonding interaction plays a vital role on the relative stabilities of 5-HT-H20 complexes.展开更多
Internal vibrations underlie transient structure formation,spectroscopy,and dynamics.However,at least two challenges exist when aiming to elucidate the contributions of vibrational motions on the potential energy surf...Internal vibrations underlie transient structure formation,spectroscopy,and dynamics.However,at least two challenges exist when aiming to elucidate the contributions of vibrational motions on the potential energy surfaces.One is the acquisition of well-resolved experimental infrared spectra,and the other is the development of efficient theoretical methodologies that reliably predict band positions,relative intensities,and substructures.Here,we report size-specific infrared spectra of ammonia clusters to address these two challenges.Unprecedented agreement between experiment and state-of-the-art quantum simulations reveals that the vibrational spectra are mainly contributed by proton-donor ammonia.A striking Fermi resonance observed at approximately 3210 and 3250 cm^(−1)originates from the coupling of NH symmetric stretch fundamentals with overtones of free and hydrogen-bonded NH bending,respectively.These novel,intriguing findings contribute to a better understanding of vibrational motions in a large variety of hydrogen-bonded complexes with orders of magnitude improvements in spectral resolution,efficiency,and specificity.展开更多
Growing interest in non-covalent interactions involving chalcogen atoms has been ascribed to their importance in crystal engineering, molecular recognition and macromolecular edifices. The present study is dealing wit...Growing interest in non-covalent interactions involving chalcogen atoms has been ascribed to their importance in crystal engineering, molecular recognition and macromolecular edifices. The present study is dealing with chalcogen bonds involving divalent Sulphur, Selenium and Tellurium atoms, acting as sigma-hole donors, in small-molecule compounds using the Cambridge Structural Database (CSD) in conjunction with ab initio calculations. Results derived from CSD surveys and computational study revealed that nucleophiles formed complexes with the chalcogen-bond donors R1-X-R2 (X = S, Se or Te). The main forces stabilizing the complexes were chalcogen bonds, enhanced by dispersion interactions. Complexation pattern and energetics show that nucleophile bonding at divalent S, Se and Te atoms is a relatively strong and directed interaction. The bond consists of a charge transfer from a nucleophile atom lone pair to an X-R1 or X-R2 antibonding orbital.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Project(20871101)supported by the National Natural Science Foundation of ChinaProject(09C945)supported by the Scientific Research Fund of Hunan Provincial Education Department,China
文摘First-principles calculations based on the density-functional theory were employed to study the crystal structure of vanadium phosphide compounds,such as V3P,V2P,VP,VP2 and VP4. Cohesive energy of five types of vanadium phosphide compounds was calculated to assess their structural stability. The charge density distribution and densities of states of vanadium phosphides were discussed to study further their electronic structures. The results show that the structure of metal-rich compounds is considerably more stable than the phosphorus-rich compositions,and covalent bond exists between the V and P atoms of V3P,V2P,VP,VP2 and VP4.
基金Project supported by the International Science & Technology Cooperation Project of China (Grant No 2007DFA40890)the National Natural Science Foundation of China (Grant Nos 10702056 and 10774124)the Program for New Century Excellent Talents in Fujian Province University, China
文摘This paper uses a molecular static approach with a many-body potential to investigate the surface energetic and bonding characteristics of tetrahexahedral platinum nanocrystals enclosed by high-index facets such as {210}, {310}, {410}, {520} and {730}. It mainly focuses on the effect of crystal size and surface Miller index on these characteristics. The results show that the surface energy and dangling bond density increase with decreasing diameter of tetrahexahedral nanocrystals and generally show an order of {210} 〉{730}〉 {520} 〉 {310} 〉 {410}. However, this order is not valid at crystal sizes below 7 nm or so. The results of corresponding surfaces are also presented for comparison.
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.
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.
文摘The thermal analysis of precise thermophysical data for pure fluids from electronic databases is developed to investigate the molecular interaction mechanisms and parameters and the structural features of heterogeneities in fluids. The method is based on the series expansion of thermophysical values by powers of the monomer fraction density. Unlike the virial expansion by powers of the total density, the series expansion terms in this method directly reflect properties of the corresponding cluster fractions. The internal energy had been selected among thermophysical properties as the most informative for this method. The thermal analysis of its series expansion coefficients permits to estimate the temperature dependence of the pair bond parameters, the clusters’ bond energies and equilibrium constants, the structural transitions between dominating isomers of clusters. The application of method to different pure fluids, including noble and molecular gases with van der Waals and polar molecular interactions, brings unknown clusters’ characteristics for the fluids under investigation. The thermal analysis of the ordinary and heavy Water vapors points on no trivial isotopic effects. The unpredictable growth of the pair bond energy with temperature in Alkanes points on existence in hydrocarbons of some unknown molecular interaction forces in addition to dispersion forces.
文摘Considerable interest in hydrogen bonding involving chalcogen has been growing since the IUPAC committee has redefined hydrogen bonding. Not only the focus is on unconventional acceptors, but also on donors not discussed before. It has been mentioned in previous studies that the proton of the H-C group could be involved in hydrogen bonding, but with conventional acceptors. In this study, we explored the ability of hydrogen bond formation of Se, S and Te acceptors with the H-C donor using Cambridge Structural Database in conjunction with Ab Initio calculations. In the CSD, there are respectively 256, 6249 and 11 R1,R2,-C=Se, R1,R2,-C=S and R1,R2,-C=Te structures that form hydrogen bonds, in which the N,N groups are majority. Except for C=S acceptor which can form a hydrogen bond with its C, C group, both C=Se and C=Te acceptors could form a hydrogen bond only with N,C and N,N groups. CSD analysis shows very similar d (norm) around -0.04 Å, while DFT-calculated interaction for N,C and N,N groups are also similar. Both interaction distances derived from CSD analysis and DFT-calculated interaction energies demonstrate that the acceptors form stable complexes with H-CF3. Besides hydrogen bonds, dispersion interactions are forces stabilizing the complexes since their contribution can reach 50%. Analysis of intra-molecular geometries and Ab Initio partial charges show that this bonding stems from resonance induced C<sup>δ+</sup>=X<sup>δ-</sup> dipoles. In many respects, both C=Se, C=S and C=Te are similar to C=S, with similar d (norm) and calculated interaction strengths.
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.
文摘All-electronic relativistic density functional theory (DFT) method has been used to study the U2F6 molecule. Results from calculations predict the existence of U2F6 molecule, which has been found to be stable with a multiply bonded U2 unit. The calculations also predict that D3d symmetry of U2F6 is more stable than D3h. The optimized geometries, vibrational frequencies and infrared intensities are reported for D3d symmetry of U2F6 from Becke Three-parameter Lee-Yang-Parr (B3LYP) function with triple zeta valence plus polarization functions basis set (TZP). The bond dissociation energy (BDE) for U-U bond in the U2F6 was obtained using the same method. In addition, the entropies of U2F6 have been investigated at temperature rang from 0 to 3000K in 10 steps using the B3LYP method.
基金supported by the National Key Laboratory of Shock Wave and Detonation Physics,Institute of Fluid Physics,China Academy of Engineering Physics(076100-1197F)the Defence Industrial Technology Development Program(B1520110002)the State Key Laboratory of Explosion Science and Technology,Beijing Institute of Technology(KFJJ09-5)
文摘In this paper,a primary model is established for MD(molecular dynamics) simulation for the PBXs(polymer-bonded explosives) with RDX(cyclotrimethylene trinitramine) as base explosive and PS as polymer binder.A series of results from the MD simulation are compared between two PBX models,which are represented by PBX1 and PBX2,respectively,including one PS molecular chain having 46 repeating units and two PS molecular chains with each having 23 repeating units.It has been found that their structural,interaction energy and mechanical properties are basically consistent between the two models.A systematic MD study for the PBX2 is performed under NPT conditions at five different temperatures,i.e.,195 K,245 K,295 K,345 K,and 395 K.We have found that with the temperature increase,the maximum bond length(L max) of RDX N N trigger bond increases,and the interaction energy(E N-N) between two N atoms of the N-N trigger bond and the cohesive energy density(CED) decrease.These phenomena agree with the experimental fact that the PBX becomes more sensitive as the temperature increases.Therefore,we propose to use the maximum bond length L max of the trigger bond of the easily decomposed and exploded component and the interaction energy E N-N of the two relevant atoms as theoretical criteria to judge or predict the relative degree of heat and impact sensitivity for the energetic composites such as PBXs and solid propellants.
基金Project supported by the Significant Fundation of China Academy of Engineering Physics (No. 2004Z0503) and the National Natural Science Foundation of China (No. 10176012).
文摘Molecular dynamics (MD) method was used to simulate 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) coated with fluorine containing polymers. The mechanical properties and binding energies of PBXs were obtained. It was found that when the number of chain monomers of fluorine containing polymers was the same, the elasticity of TATB/F2314 was increased more greatly than others and the binding energy of TATB/F2311 was the largest among four PBXs. Detonation heat and velocity of such four PBXs were calculated according to theoretical and empirical formulas. The results show that the order of detonation heat is TATB〉TATB/PVDF〉TATB/F2311〉TATB/ F2314 〉 TATB/PCTFE while the order of detonation velocity is TATB/PVDF 〈 TATB/F2311 〈 TATB/F2314 〈 TATB/PCTFE 〈TATB.
基金the National Natural Science Foundation of China(Grant Nos.10176012 and 20173028).
文摘The molecular simulations of the well-known high explosive β-HMX (cyclotetramethylene tetranitramine) anditsfluorine containing polymer-bonded explosives(PBXs) were carried out with the combination method of quantum mechanics, molecular mechanics and molecular dynamics. The atomic cluster model, containing the β-HMX molecule and the polymer molecule whose chain dimension was about the same as β-HMX’s, was fully optimized by AM1 and PM3 semi-empirical molecular orbital and molecular mechanical methods using COMPASS and PCFF force field. Then the calculated binding energy is found to be linearly correlated to each other. Molecular dynamics simulations using COM- PASS force field were performed for β-HMX crystal and the PBXs involving β-HMX and a series of fluorine containing polymers. Their elastic coefficients, moduli and Poisson’s ratios were calculated. It is found that the mechanical prop- erties of β-HMX can be effectively improved by blending with fluorine containing polymers in small amounts.
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.
文摘The energies, geometries and harmonic vibrational frequencies of 1 : 1 5-hydroxytryptamine-water (5-HT-H20) complexes are studied at the MP2/6-311 + + G(d,p) level. Natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM) analyses and the localized molecular orbital energy decomposition analysis (LMO-EDA) were performed to explore the nature of the hydrogen-bonding interactions in these complexes. Various types of hydro- gen bonds (H-bonds) are formed in these 5-HT-H20 complexes. The intermolecular C4H55HT'"Ow H-bond in HTW3 is strengthened due to the cooperativity, whereas no such cooperativity is found in the other 5-HT-H20 complexes. H-bond in which nitrogen atom of amino in 5-HT acted as proton donors was stronger than other H-bonds. Our researches show that the hydrogen bonding interaction plays a vital role on the relative stabilities of 5-HT-H20 complexes.
基金supported by the National Natural Science Foundation of China(grant nos.21673231 and 21688102)the Strategic Priority Research Program of the Chinese Academy of Sciences(CAS)(grant no.XDB17000000)+3 种基金the Dalian Institute of Chemical Physics(DICP DCLS201702)K.C.Wong Education Foundation(GJTD-2018-06)supported by the Ministry of Science and Technology of Taiwan(MOST-106-2811-M-001-051 and MOST-107-2628-M-001-002-MY4)the Academia Sinica.
文摘Internal vibrations underlie transient structure formation,spectroscopy,and dynamics.However,at least two challenges exist when aiming to elucidate the contributions of vibrational motions on the potential energy surfaces.One is the acquisition of well-resolved experimental infrared spectra,and the other is the development of efficient theoretical methodologies that reliably predict band positions,relative intensities,and substructures.Here,we report size-specific infrared spectra of ammonia clusters to address these two challenges.Unprecedented agreement between experiment and state-of-the-art quantum simulations reveals that the vibrational spectra are mainly contributed by proton-donor ammonia.A striking Fermi resonance observed at approximately 3210 and 3250 cm^(−1)originates from the coupling of NH symmetric stretch fundamentals with overtones of free and hydrogen-bonded NH bending,respectively.These novel,intriguing findings contribute to a better understanding of vibrational motions in a large variety of hydrogen-bonded complexes with orders of magnitude improvements in spectral resolution,efficiency,and specificity.
文摘Growing interest in non-covalent interactions involving chalcogen atoms has been ascribed to their importance in crystal engineering, molecular recognition and macromolecular edifices. The present study is dealing with chalcogen bonds involving divalent Sulphur, Selenium and Tellurium atoms, acting as sigma-hole donors, in small-molecule compounds using the Cambridge Structural Database (CSD) in conjunction with ab initio calculations. Results derived from CSD surveys and computational study revealed that nucleophiles formed complexes with the chalcogen-bond donors R1-X-R2 (X = S, Se or Te). The main forces stabilizing the complexes were chalcogen bonds, enhanced by dispersion interactions. Complexation pattern and energetics show that nucleophile bonding at divalent S, Se and Te atoms is a relatively strong and directed interaction. The bond consists of a charge transfer from a nucleophile atom lone pair to an X-R1 or X-R2 antibonding orbital.