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.     

三硝基甲烷键离解能和生成焓的理论计算

采用密度泛函(DFT)四种交换/相关函数(B3LYP、B3P86、B3PW91和PBE0)结合不同的基函数,求得了三硝基甲烷C-NO2键的离解能(BDE),并且通过合理选择参考物硝基甲烷,设计等键等电子对反应,计算了气相三硝基甲烷分子的生成焓(HOF).与实验数据进行比较,PBE0/6-31g*计算出的BDE值最好,误差为-2.1 kcal mol-1;PBE0密度泛函结合带极化函数的6-31g基组得到的HOF值与实验值吻合的最好(误差在0.1 kcal mol-1以内).     

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。     

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。     

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。     

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。     

过渡金属碳化物CrC^＋,MoC^＋和WC^＋的键离解能研究

首次报道了ＣｒＣ＾＋,ＭｏＣ＾＋和分子离子键离解能。通过测量Ｍ＾＋＋ＸＹ→ＭＸ＾＋＋Ｙ的反应阈值,其中ＸＹ是已知键离解能的双原子分子。可以推出ＭＸ＾＋的键离解能,利用同步辐射真空紫外光电离原理,电离过渡金属羰基化合物Ｍ（ＣＯ）６,从而产生金属离子Ｍ＾＋和金属离子碳化物ＭＣ＾＋,测量Ｍ＾＋和ＭＣ＾＋的出现势,结合已知的ＣＯ分子键离解能Ｄ０（Ｃ－Ｏ）＝１１．０９ｅＶ和图中的关系,可以求得ＭＣ＾＋的键离     

氢键和分子-离子相互作用对奥克托今(HMX)引发键影响的理论研究

为了寻找能够降低炸药感度的方法,借助B3LYP和MP2(full)理论,在B3LYP/6-311++G(2df,2p)、B3LYP/aug-cc-p VTZ和MP2(full)/6-311++G(2df,2p)三种水平下,分别研究了与HMX形成的12种复合物(六种氢键复合物和六种分子-离子复合物),并对引发键N-NO2键长和强度的变化及硝基电荷的变化等进行了详细的考量,最后借助分子中原子(AIM)理论揭示了结构和能量变化的本质.结果表明,在形成复合物后,引发键键长变短,离解能增大,硝基电荷增多,引发键增强,感度降低,同时引发键离解能的变化(ΔBDEs)与这两种相互作用能呈良好的线性关系(R2=0.9984).     

氢键和分子-离子相互作用对奥克托今(HMX)引发键影响的理论研究

为了寻找能够降低炸药感度的方法,借助B3LYP和MP2(full)理论,在B3LYP/6-311+ +G(2df,2p)、B3LYP/aug-cc-pVTZ和MP2(full)/6-311++G(2df,2p)三种水平下,分别研究了与HMX形成的12种复合物（六种氢键复合物和六种分子-离子复合物）,并对引发键N-NO2键长和强度的变化及硝基电荷的变化等进行了详细的考量,最后借助分子中原子(AIM)理论揭示了结构和能量变化的本质.结果表明,在形成复合物后,引发键键长变短,离解能增大,硝基电荷增多,引发键增强,感度降低,同时引发键离解能的变化(ΔBDEs)与这两种相互作用能呈良好的线性关系(R2=0.9984).     

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.     

The evaluation of bond dissociation energies for NO2 scission in nitro compounds using density functional and complete basis set methods

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.     

Accurate studies of dissociation energies and vibrational energies on alkali metals

This paper studies full vibrational spectra {Ev} and molecular dissociation energies De by using conventional least-squares （LS） fitting and an algebraic method （AM） proposed recently for 10 diatomic electronic states of ^7Li2, Na2, NaK and NaLi molecules based on some known experimental vibrational energies in a subset [Ev^expt] respectively. Studies show that： （1） although both the full AM spectrum {Ev^AM} and the LS spectrum {Ev^LS} can reproduce the known experimental energies in [Ev^expt], the {EAM} is superior to the {Ev^LS} in that the high-lying AM vibrational energies which may not be available experimentally have better or much better accuracy than those LS counterparts in {Ev^LS}, and so is the AM dissociation energy De^AM; （2） the main source of the errors in the data obtained by using the LS fitting is that the fitting which is just a pure mathematical process does not use any physical criteria that must be satisfied by the full vibrational spectrum, while the AM method does. This study suggests that when fitting or solving a physical equation using a set of source data, it is important not only to apply a proper mathematical tool, but also to use correct physical criteria which measure the physical properties of the data, kick out those data having bigger errors, and impose conditional convergence on the numerical process.     

Density functional theory calculations on S―S bond dissociation energies of disulfides

The S―S bond cleavage plays an important role in affecting the reactivity or biological activities of disulfide‐based compounds. With the aid of density functional theory (DFT) calculations, the present study focuses on predicting the S―S bond dissociation energies (BDEs) of disulfides. The range of BDEs of different types of disulfides was constructed for the first time. It was found that the electronic effect (and especially the conjugation effect) of substituents is predominant in determining the S―S bond strength of disulfides. By contrast, the steric effect is insignificant for most molecules due to the long S―S bond distances. We hope that the present study will benefit the future development of more powerful strategies in activating the S―S bond of disulfides. Copyright © 2015 John Wiley & Sons, Ltd.     

双原子分子振动能谱与离解能的精确研究

代数方法(AM)的建立解决了实验方法和精确量子力学理论方法难以获得双原子分子的包含最高振动能级在内的所有高阶振动能级的精确数值这一问题.基于LeRoy与Bernstein的工作,孙卫国等又建立了精确计算双原子分子离解能的新解析表达式.应用新公式和代数方法(AM),研究了一些双原子分子部分电子态的振动能谱和分子离解能,获得了与实验值符合非常好的理论结果.该方法在理论上提供了获得双原子分子完全振动能谱和精确分子离解能的物理新方法.     

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.     

Accurate studies on dissociation energies of diatomic molecules

The molecular dissociation energies of some electronic states of hydride and N2 molecules were studied using a parameter-free analytical formula suggested in this study and the algebraic method (AM) proposed recently. The results show that the accurate AM dissociation energies DeAM agree excellently with experimental dissociation energies Deexpt, and that the dissociation energy of an electronic state such as the 23△g state of 7Li2 whose experimental value is not available can be predicted using the new formula.