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金属钒弹性波速与热力学函数的理论计算 总被引:2,自引:1,他引:1
在全电子水平上,基于广义梯度近似(GGA)的密度泛函理论和全势能线性缀加平面波方法(FLAPW)计算了钒的晶格参数,弹性波速和格临爱森参数.在德拜模型的基础上,利用弹性波速方法和原子位移方法分别计算了钒的德拜频率,以及在标准条件下(298.15 K,1atm)的热容,熵等热力学函数,并与实验值进行了比较. 相似文献
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氦气(He)在众多科学和工业领域中都具有非常广泛的应用, He资源的短缺和需求的不断增长使得He分离具有极其重要的意义.石墨烷合成简单、晶体结构稳定,是一种用于构建气体分离膜的潜在理想二维材料.本文通过第一性原理计算,对四种具有不同尺寸冠醚孔的石墨烷膜(crown ether graphane-n, CG-n,n=3, 4, 5, 6)的He分离性能进行了研究.计算结果表明,四种冠醚石墨烷结构都具有较高的热力学、化学稳定性,并且CG-5和CG-6具有合适的孔径,可用于He的有效筛分.在11种气体分子(He, Ne, Ar, H2, CO,NO, NO2, N2, CO2, SO2和CH4)中, He最容易通过CG-n膜,其能垒分别为4.55, 1.05, 0.53和0.01 eV.据我们所知, He通过CG-6的能垒是迄今为止报道的最低值,将可显著地提升He的分离效率.基于阿伦尼乌斯方程的选择性计算结果表明, CG-5在较宽的温度范围内(0—600 K)都表现出优异的He选择性... 相似文献
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选择性催化还原脱硝技术效率高,有望应用于汽车尾气中NO_x的排放控制.本文采用5种不同的密度泛函理论,计入色散校正项的影响,预测了选择性催化还原脱硝反应体系中各种气体的标准生成焓以及温度从0 K到1000 K时各气体的焓变。与实验比较结果表明,广义密度梯度近似中的BLYP泛函和B3LYP泛函对标准生成焓的预测偏差最小,而本文检验的所有密度泛函理论都能很好地预测气体在0~1000 K温度范围内的焓变,可以用于选择性催化还原脱硝反应体系的热量恒算。 相似文献
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三硝基甲烷键离解能和生成焓的理论计算 总被引:5,自引:0,他引:5
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). 相似文献
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应用Gaussian 98程序对U-H2O体系所有可能的构型进行优化计算-采用密度泛函 理论的B3L YP方法和MP2方法,对铀原子采用相对论有效原子实势及(6s5p2d4f)/[3s3p2d2f]收缩价基 集合,氧、氢原子采用6-311G**全电子基集合-计算得到了6种五重态的相对稳 定结构 的电子状态、几何结构、能量、谐振频率、力学性质和电性质等-结果表明,H2 O蒸汽在金 属铀表面的反应首先是铀和氧的相互作用-对C2v关键词:
密度泛函理论
B3LYP
分子结构
热力学函数 相似文献
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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. 相似文献
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以统计热力学和化学平衡理论为基础,引用原子、分子的光谱数据,计算了在温度300~20000K范围内,双原子分子体系的热平衡等离子体的热力学函数(H、Cp,m)。给出了氮等离子体体系的分子离解度、电离度和摩尔定压热容随温度变化的关系曲线。所得结果在较低温度范围与经验公式表达的结果良好相符。对较高温度区间的结果作了分析和讨论,并利用最小二乘法给出了氮体系的摩尔热容量的拟合公式。为热等离子体的应用提供了可以参考的数据。 相似文献
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Structures and thermochemistry of methyl ethyl sulfide and its hydroperoxides: HOOCH2SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH,and radicals
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Hydroperoxides and the corresponding peroxy radicals are important intermediates during the partial oxidation of methyl ethyl sulfide (CH3SCH2CH3) in both atmospheric chemistry and in combustion. Structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔHfo, So and Cp(T)) of 3 corresponding hydroperoxides CH2(OOH)SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH of methyl ethyl sulfides, and the radicals formed via loss of a hydrogen atom are important to understanding the oxidation reactions of MES. The lowest energy molecular structures were identified using the density functional B3LYP/6‐311G(2d,d,p) level of theory. Standard enthalpies of formation (ΔHfo298) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods. Isodesmic reactions were used to determine ?Hfo values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31G(d,p) level theory. Contributions for So298 and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions. The recommended values for enthalpies of formation of the most stable conformers of CH3SCH2CH2, CH2(OOH)SCH2CH3, CH3SCH(OOH)CH3, and CH3SCH2CH2OOH are ?14.0, ?33.0, ?37.2, and ?32.7 kcal/mol, respectively. Group additivity values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxides. Groups for use in group additivity estimation of sulfur peroxide thermochemical properties were developed. 相似文献
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We investigated the influence of the precursor, graphite, size on the synthesis and reduction of graphite oxide. Three precursors of graphite with different size were used to synthesize the graphite oxide which was consecutively reduced by hydrazine of different concentration ratios. Size dependent effect on the reduction of the graphite oxide was found, and the graphite oxide of the smallest size provided the best reduction result. Electrochemical properties of the reduced graphene oxide were investigated in both of the base and acid electrolytes, finding the reduced graphene oxide of the smallest size gives the best electrochemical performance due to the high reduction. Therefore, the precursor size is a very important factor in the synthesis and reduction of graphite oxide, affecting the electrochemical performance considerably for the energy storage applications. 相似文献
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为探讨膨胀石墨作为3 mm波干扰材料的消光、散射特性及其影响因素, 基于有限长度、有限电导率圆柱状导体的电磁散射, 利用矩量法建立了膨胀石墨的消光、散射、吸收及后向散射截面(雷达散射截面RCS)的计算式. 运用Mathematica编程计算并分析了膨胀石墨长度、半径、电导率、磁导率等因素与膨胀石墨消光、散射、吸收截面及RCS的关系. 结果表明: 当膨胀石墨的长度为1.5 mm、半径为0.05 mm时, 具有较好的消光、散射效果; 适当增大膨胀石墨的电导率、磁导率, 有利于提高其消光、散射能力. 本研究为探索增强膨胀石墨干扰3 mm波效果的技术途径提供了有价值的参考.
关键词:
膨胀石墨
石墨层间化合物
消光截面
矩量法 相似文献
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Using ab initio plane-wave pseudo-potential density functional theory method,the elastic constants and band structures of stishovite were calculated.The calculated elastic constants under ambient conditions agree well with previous experimental and theoretical data.C13,C33,C44,and C66 increase nearly linearly with pressure while C 11 and C 12 show irregularly changes with pressure over 20 GPa.The shear modulus(C11-C12)/2 was observed to decrease drastically between 40 GPa and 50 GPa,indicating acoustic mode softening in consistency with the phase transition to CaCl 2-type structure around 50 GPa.The calculated band structures show no obvious difference at 0 and 80 GPa,being consistent with the high incompressibility of stishovite.With a quasi-harmonic Debye model,thermodynamic properties of stishovite were also calculated and the results are in good agreement with available experimental data. 相似文献
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利用基于密度泛函理论的第一性原理全势线性缀加平面波方法,研究了立方反ReO3结构Cu3N在零温(0K)零压下的平衡晶格常数、体弹模量及其对压强的一阶导数,计算结果与其他实验及理论结果基本相符.同时得出Cu3N的弹性常数,Poisson比等,并分析出Cu3N在零温零压下是稳定的.通过准谐Debye模型计算Cu3N的热力学性质,得到了Cu3N的晶格常数、等压比热容、等容比热容、热胀系数与温度和压强之间的关系,同时计算出不同温度不同压强下其体弹模量及Debye温度的值。 相似文献
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Alfred P. Chernyshev 《Physics letters. A》2010,374(45):4622-4624
In the framework of the Landau mean-field theory, the novel thermodynamic model was developed to describe the behavior of the melting enthalpy and entropy of nano-objects having the characteristic size less than 10 nm. It is implied that nano-objects of the critical sizes undergo the second-order transition instead of usual melting. For the first time it was revealed that the melting enthalpy and entropy of nanoparticles, having the characteristic size less than critical one, increase with decreasing the characteristic size of nanoparticles. 相似文献
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探讨了纳米颗粒和纳米块材摩尔定压热容 CP(T)的理论计算方法,提出了利用纳米颗粒的熔点数据来计算纳米颗粒的德拜(Debye)温度、体膨胀系数和CP(T)的理论公式,以铜纳米颗粒为例,CP(T)的理论计算值与实验值符合较好;提出了纳米块材的Debye温度随块材密度变化的关系式,随着块材密度减小,Debye温度降低;铜纳米块材CP(T)的理论计算值与实验值也符合较好;纳米块材的体
关键词:
纳米颗粒
纳米块材
CP(T)')" href="#">摩尔定压热容CP(T)
德拜温度 相似文献