硝化纤维素生成焓、键离解能及爆轰性能的理论研究

运用密度泛函理论方法结合等键反应,研究了硝化纤维素(NC)单体的生成热及其不同位置上氧硝基键(ONO2)的键离解能,基于半经验的Kamlet-Jacobs方程估算了其爆速与爆压。结果表明:B3LYP和B3P86两种方法得到的计算结果较为接近,生成热均为负值,其大小与氧硝基的数目有关,与氧硝基的取代位置无关。理论计算得到的氧硝基键的键离解能与含氮量无关,而是与实际断裂的氧硝基键的数目相关。爆速和爆压的计算表明,NC单体中所含氧硝基的数量增多,会降低其爆速和爆压。     

含硝基烷基的一些CHNO多硝基化合物的C-NO2键离解能计算——应用于撞击感度

用密度泛函方法,在B3LYP/6-31G*水平对五个含硝基烷基的硝基芳香族炸药分子和四个含硝基烷基的苯酸酯炸药分子进行了几何结构全优化、能量和频率计算.并分别对这两类炸药分子苯环上的C-NO2和烷基上的C-NO2键离解能进行了同等水平的计算.结果表明,这两类分子中的最弱键均是烷基上的C-NO2键.进一步分析实验撞击感度与分子中最弱键离解能量的关系.结果表明,最弱键离解能BDE是表征炸药撞击感度的重要指针,但不是唯一指针.除了BDE,炸药的撞击感度可能还受其它因素或反应途径的影响.     

硝酸丙酯键离解能和热解机理的密度泛函理论研究

 采用B3LYP方法、在6-31G*基组水平上,优化了硝酸丙酯单体的平衡几何构型,计算了分子中各键的离解能。结果表明该分子中最弱的键为O—NO₂键,次弱键为C—O键。同时研究了热解机理,探索性的预测了断裂O—NO₂键及C—O键后的产物,并采用从头算法、半经验方法和密度泛函理论分别计算了硝酸丙酯的生成热,由半经验方法中的PM3得到的数值和实验结果符合较好。     

含能材料中键离解能的密度泛函理论计算

通过计算一个包括臭氧,硝基甲烷以及1,3,5 -三硝基-1,3,5-三氮杂环已烷(RDX)在内的典型系统的键离解能,对由四种交换/相关函数(BLYP,B3LYP,B3PW91和B3P86)加上不同的基函数组合而成的多种密度泛函方法的准确性进行了比较研究.结果表明:B3P86/6-31G**是计算该系统C-NO2,O-O和N-NO2键离解能的最可靠的方法.     

C-H,C-N,C-O,N-N的键离解能和键长的计算

用B3LYP/6-311G**和CCSD/cc-pVDZ方法对CH4、CH3、CN、CO、N2、CH3NH2、CH3NO2、NH2NO2八个分子中的C-H、C-N、C-O、N-N键离解能进行计算,通过比较研究可知,计算CH3、CH3NH2、CH3NO2分子中的C-H键离解能和CN、CO、N2分子的键离解能用B3LYP/6-311G**方法可靠,而计算CH3-H、CH3-NH2、CH3-NO2和NH2-NO2分子的键离解能用CCSD/cc-pVDZ方法更可信;用以上二种方法对本文的八个分子的平衡几何结构进行优化求出所需的键长,通过比较可知,CH4、CH3、CN、CO、N2分子用B3LYP/6-311G**的方法进行平衡几何优化求得的键长更可靠,而CH3NO2、NH2NO2、CH3NH2分子则用CCSD/cc-pVDZ方法优化出的键长是更可信.     

C-I键均裂解离焓的密度泛函理论研究

在高级别理论(包含使用外推基组的MP2和CCSD(T))方法及大量密度泛函方法的理论基础上, 研究了不同种类有机碘化物的C-I键均裂解离能. 密度泛函方法的系统性评估计算结果表明,MPWLYP1M方法的计算精度最高. 运用该方法系统地考查了C(sp³)-I和C(sp²)-I键的取代基效应. 以及取代碘苯及取代苄基碘化物的远程取代基效应. 此外,在MPWLYP1M方法的基础上研究了典型五元及六元芳香杂环碘化物的C-I键解离焓值.     

含alphaC-H键的硝基芳香族炸药分子的C-NO2键离解能研究

采用密度泛函理论中的B3LYP方法,取6-31G*基组,对含alpha C-H键的硝基苯类炸药的分子结构和能量,以及C-NO2键离解能等进行计算,讨论了含alpha C-H键的硝基苯类炸药分子中C-NO2键离解能的强弱与其位置的关系。研究表明:alpha C-H键邻位的C-NO2键离解能比对位的C-NO2键离解能弱,邻位中又以受alpha C-H键影响最大的C-NO2键离解能最弱。     

固相硝基甲烷相变的第一性原理计算

研究极端条件下固相分子晶体含能材料的相变机理,对于人们认识固相含能材料的爆轰反应有着重要的意义.采用基于校正密度泛函理论的第一性原理方法研究固相硝基甲烷在静水压下的行为.分析晶格参数a,b和c轴随压强的变化,发现在1 GPa到12 GPa时晶格参数出现不连续的变化,表明体系发生相变.在相变时最大的二面角从155.3?增加到177.5?,二面角的增加限制CH3官能团自由旋转,使得C-N和C-H键的键长发生变化.在相变之前,体系主要存在由C-H···O组成的分子间的氢键,而在相变之后存在分子内的H···O和分子间C-H···O组成的氢键.此外通过对硝基甲烷体系的电子结构进行计算,发现相变会影响带隙随压强的变化,而且还会影响费米能级附近的态密度结构.     

镍-配体键解离焓的密度泛函理论研究

许多镍催化反应中包含镍与配体(如氮杂环卡宾、三级膦等)配位键的断裂与生成过程,准确计算Ni-L键解离焓有助于理解这类反应．以近期Nolan小组报道的Ni-L键的解离焓为基准,评估不同密度泛函理论(包括B3LYP、M06、MPWB1K等)、不同基组(包括Ni上的赝势基组和其它原子上的全电子基组)的计算准确性,发现MPWB1K/LanL2DZ:6-31+G(d,p)//MPWB1K/LanL2DZ:6-31G(d)方法得出的结果与实验值吻合度最佳,溶剂化效应的相关计算表明CPCM和PCM溶剂化模型表现良好．     

键解离焓的理论方法研究

The density functional theory (DFT) is the most popular method for evaluating bond dis-sociation enthalpies (BDEs) of most molecules. Thus, we are committed to looking for alternative methods that can balance the computational cost and higher precision to the best for large systems. The performance of DFT, double-hybrid DFT, and high-level com-posite methods are examined. The tested sets contain monocyclic and polycyclic aromatic molecules, branched hydrocarbons, small inorganic molecules, etc. The results show that the mPW2PLYP and G4MP2 methods achieve reasonable agreement with the benchmark values for most tested molecules, and the mean absolute deviations are 2.43 and 1.96 kcal/mol after excluding the BDEs of branched hydrocarbons. We recommend the G4MP2 is the most appropriate method for small systems (atoms number ≤20); the double-hybrid DFT methods are advised for large aromatic molecules in medium size (20 ≤atoms number ≤50), and the double-hybrid DFT methods with empirical dispersion correction are recommended for long-chain and branched hydrocarbons in the same size scope; the DFT methods are advised to apply for large systems (atoms number ≥50), and the M06-2X and B3P86 methods are also favorable. Moreover, the di erences of optimized geometry of different methods are discussed and the effects of basis sets for various methods are investigated.     

聚对苯二甲酸丁二醇酯二聚体键离能的理论研究

采用密度泛函理论方法对聚对苯二甲酸丁二醇酯(PBT)二聚体的键离能进行了计算.为了选取较为精确的方法来计算PBT各个键的键离能,以与PBT具有相同的酯基官能团的乙酸乙酯为模型参照物.采用M062X, B3P86, M06, PBE0, wB97xD方法分别在基组6-31G(d), 6-311G(d), 6-311+G(d, p), 6-311++G(d, p), cc-pVDZ, cc-pVTZ水平下对乙酸乙酯的键离能进行计算.通过对比计算结果与iBonD数据库的乙酸乙酯实验测定值可知,M062X在基组6-311G(d)水平下计算结果与实验值最为接近.因此,本研究采用M062X方法在基组6-311G(d)水平下对聚对苯二甲酸丁二醇酯(PBT)二聚体的键离能进行计算.计算结果表明：在PBT的各键中C-C_arcmatic键的键离能最大,主链上的C-C键离能最小,为370.9 kJ/mol.其次就是C-O键,为404.6 kJ/mol.基于PBT键离能的计算结果,设计了3条PBT二聚体热降解过程可能形成的反应路径,分析了热解产物的形成机理.结果表明PBT二聚体热解过程可...     

两种太根(Tri-EGDN和Tetra-EGDN)的几何结构和键裂解能的理论研究

利用密度泛函理论(DFT)中的B3LYP、B3PW91、B3P86方法研究了二缩三乙二醇二硝酸酯(Tri-EGDN)和三缩四乙二醇二硝酸酯(Tetra-EGDN)的平衡分子构型、前线轨道能(EHOMO、ELUMO)、能差(ΔE=ELUMO-EHOMO)和O-NO2键的裂解能(BDE),并分析了两种硝酸酯分子和对应自由基的热稳定性.Tri-EGDN和Tetra-EGDN中的O-NO2键的裂解能用B3P86方法计算最接近真实值.由O-NO2键的裂解能很好地符合文献中对应物质的表观活化能,推知两种物质的热分解反应只是单分子O-NO2键的均裂反应.     

The enthalpies of dissociation of the N?O bonds in two quinoxaline derivatives

The present work reports the first experimental thermochemical study of mono‐N‐oxides derived from quinoxaline, namely, 3‐methoxycarbonyl‐2‐methyl‐quinoxaline N‐oxide and 3‐ethoxycarbonyl‐2‐methyl‐quinoxaline N‐oxide. The values of the enthalpies of formation, in the condensed state, and of the enthalpies of sublimation, derived from static bomb calorimetry and Calvet microcalorimetry measurements, respectively, are combined to derive the standard molar enthalpies of formation in the gaseous phase for these two compounds. From the latter values, the first and second N? O bond dissociation enthalpies for the corresponding di‐N‐oxides have been obtained. The gas‐phase experimental results are also compared with calculated data obtained with a density functional theory approach. Copyright © 2008 John Wiley & Sons, Ltd.     

Quantum chemical calculations of bond dissociation energies for COOH scission and electronic structure in some acids

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.     

Theoretical studies on a series of nitroaliphatic energetic compounds

Density functional theory calculations at the B3LYP/6-311G＊＊ level are performed to study the geometric and elec- tronic structures of a series of nitroaliphatic compounds. The heats of formation （HOF） are predicted through the designed isodesmic reactions. Thermal stabilities are evaluated via the homolytic bond dissociation energies （BDEs）. Further, the correlation is developed between impact sensitivity h50% and the ratio （BDE/E） of the weakest BDE to the total energy E containing zero point energy correction. In addition, the relative stability of the title compounds is evaluated based on the analysis of calculated Mulliken population and the energy gaps between the frontier orbitals. The calculated BDEs, HOFs, and energy gaps consistently indicate that compound 1,1,1,6,6,6-hexanitro-3-hexyne is the most unstable and the compound 3,3,4,4,-tetranitro-hexane is the most stable. These results provide basic information for the molecular design of novel high energetic density materials.     

Theoretical Study of the C-Cl Bond Dissociation Enthalpy and Electronic Structure of Substituted Chlorobenzene Compounds

利用密度泛函(DFT)三种交换/相关函数(B3LYP, B3PW91,B3P86)结合6-31G**和6-311G**基组,计算了13个取代氯苯化合物的键离解能. 结果表明B3P86/6-311G**方法是计算取代氯苯化合物键离解能的可信方法,研究发现C-Cl键的键离解能与所使用的基组和计算方法密切相关,取代基对C-Cl键的键离解能的影响不明显. 研究了目标化合物的前线轨道能级差,并对取代氯苯化合物的热稳定性做了评估.     

多硝基苯酸酯炸药分子键离解能与撞击感度关系研究

用密度泛函方法,在B3LYP-6-31G*、B3P86/6-31G*和B3LYP-6-311G*三种理论水平对四个含硝基烷基的苯酸酯炸药分子进行了几何结构全优化、能量和频率计算。并对这些炸药分子苯环上的C-NO2和烷基上的C-NO2键离解能分别进行了三种理论水平的计算。结果表明,这类分子中的最弱键是烷基上的C-NO2键。进一步分析实验撞击感度与分子中最弱键离解能量的关系,结果表明,分子最弱键离解能与分子总能量的比值BDE/E和实验撞击感度h50%之间存在一个几乎线性的关联关系。BDE/E是表征炸药撞击感度的一个实用的合理指针。