The reHISS Three-Range Exchange Functional with an Optimal Variation of Hartree–Fock and Its Use in the reHISSB-D Density Functional Theory Method

In the present study, we have reparametrized the HISS exchange functional. The new “reHISS” exchange provides a balance between short- and mid-range Hartree–Fock exchange (HFX) and a large total HFX coverage, with a fast convergence to zero HFX in the long range. The five parameters in this functional (according to equations 3 and 4 in the main text) are c_SR = 0.15, c_MR = 2.5279, c_LR = 0, ω_SR = 0.27, and ω_LR = 0.2192. The combination of reHISS exchange with a reparametrized B97c-type correlation functional (Chan et al., J. Comput. Chem. 2017 , 38, 2307) and a D2 dispersion term (s₆ = 0.6) gives the reHISSB-D method. We find it to be more accurate than related screened-exchange methods and, importantly, its accuracy is more uniform across different properties. Fundamentally, our analysis suggests that the good performance of the reHISS exchange is related to it capturing a near-optimal proportion of HFX in the range of interelectronic distance that is important for many chemical properties, and we propose this range to be approximately 1–4Å. © 2018 Wiley Periodicals, Inc.     

Ab Initio Thermochemistry of Solid‐State Materials

In this contribution we introduce an electronic‐structure‐theory‐based approach to a quantum‐chemical thermochemistry of solids. We first deal with local and collective atomic displacements and explain how to calculate these. The fundamental importance of the phonons, their dispersion relations, their experimental determination as well as their calculation is elucidated, followed by the systematic construction of the thermodynamic potentials on this basis. Subsequently, we provide an introduction for practical computation as well as a critical analysis of the level of accuracy obtainable. We then show how different solid‐state chemistry problems can be solved using this approach. Among these are the calculation of activation energies in perovskite‐like oxides, but we also consider the use of theoretical vibrational frequencies for determining crystal structures. The pressure and temperature polymorphism of elemental tin which has often been classically described is also treated, and we energetically classify the metastable oxynitrides of tantalum. We also demonstrate, using the case of high‐temperature superconductors, that such calculations may be used for an independent evaluation of thermochemical data of unsatisfactory accuracy. Finally, we show the present limits and the future challenges of the theory.     

Thermal Behavior and Non-isothermal Decomposition Reaction Kinetics of NEPE Propellant with Ammonium Dinitramide

Thermal decomposition behavior and non‐isothermal decomposition reaction kinetics of nitrate ester plasticized polyether NEPE propellant containing ammonium dinitramide (ADN), which is one of the most important high energetic materials, were investigated by DSC, TG and DTG at 0.1 MPa. The results show that there are four exothermic peaks on DTG curves and four mass loss stages on TG curves at a heating rate of 2.5 K·min^?1 under 0.1 MPa, and nitric ester evaporates and decomposes in the first stage, ADN decomposes in the second stage, nitrocellulose and cyclotrimethylenetrinitramine (RDX) decompose in the third stage, and ammonium perchlorate decomposes in the fourth stage. It was also found that the thermal decomposition processes of the NEPE propellant with ADN mainly have two mass loss stages with an increase in the heating rate, that is the result of the decomposition heats of the first two processes overlap each other and the mass content of ammonium perchlorate is very little which is not displayed in the fourth stage at the heating rate of 5, 10, and 20 K·min^?1 probably. It was to be found that the exothermal peak temperatures increased with an increase in the heating rate. The reaction mechanism was random nucleation and then growth, and the process can be classified as chemical reaction. The kinetic equations of the main exothermal decomposition reaction can be expressed as: dα/dt=10^12.77(3/2)(1?α)[?ln(1?α)]^1/3 e^{?1.723×104/T}. The critical temperatures of the thermal explosion (T_be and T_bp) obtained from the onset temperature (T_e) and the peak temperature (T_p) on the condition of β→0 are 461.41 and 458.02 K, respectively. Activation entropy (ΔS^≠), activation enthalpy (ΔH^≠), and Gibbs free energy (ΔG^≠) of the decomposition reaction are ?7.02 J·mol^?1·K^?1, 126.19 kJ·mol^?1, and 129.31 kJ·mol^?1, respectively.     

8-羟基喹啉与醋酸钴固相配位反应的热化学研究

用具有恒定温度环境的反应热量计,以 ４ ｍ ｏｌ· Ｌ－ １ Ｈ Ｃｌ溶液为量热溶剂,测得８羟基喹啉与醋酸钴固相反应焓Δｒ Ｈｍ ＝ ２９．６８ ｋ Ｊ·ｍ ｏｌ－ １,计算了配合物 Ｃｏ（ｏｘｉｎ）２ ·２ Ｈ２ Ｏ 的标准生成焓Δｆ Ｈｍ ＝ － ７６４．６ ｋ Ｊ·ｍ ｏｌ     

Thermodynamic and ab initio analysis of the controversial enthalpy of formation of formaldehyde.

There are two values, -26.0 and -27.7 kcal mol(-1), that are routinely reported in literature evaluations for the standard enthalpy of formation, Delta(f) H(o)(298), of formaldehyde (CH(2)=O), where error limits are less than the difference in values. In this study, we summarize the reported literature for formaldehyde enthalpy values based on evaluated measurements and on computational studies. Using experimental reaction enthalpies for a series of reactions involving formaldehyde, in conjunction with known enthalpies of formation, its enthalpy is determined to be -26.05+/-0.42 kcal mol(-1), which we believe is the most accurate enthalpy currently available. For the same reaction series, the reaction enthalpies are evaluated using six computational methods: CBS-Q, CBS-Q//B3, CBS-APNO, G2, G3, and G3B3 yield Delta(f) H(o)(298)=-25.90+/-1.17 kcal mol(-1), which is in good agreement to our experimentally derived result. Furthermore, the computational chemistry methods G3, G3MP2B3, CCSD/6-311+G(2df,p)//B3LYP/6-31G(d), CCSD(T)/6-311+G(2df,p)//B3LYP/6-31G(d), and CBS-APNO in conjunction with isodesmic and homodesmic reactions are used to determine Delta(f) H(o)(298). Results from a series of five work reactions at the higher levels of calculation are -26.30+/-0.39 kcal mol(-1) with G3, -26.45+/-0.38 kcal mol(-1) with G3MP2B3, -26.09+/-0.37 kcal mol(-1) with CBS-APNO, -26.19+/-0.48 kcal mol(-1) with CCSD, and -26.16+/-0.58 kcal mol(-1) with CCSD(T). Results from heat of atomization calculations using seven accurate ab initio methods yields an enthalpy value of -26.82+/-0.99 kcal mol(-1). The results using isodesmic reactions are found to give enthalpies more accurate than both other computational approaches and are of similar accuracy to atomization enthalpy calculations derived from computationally intensive W1 and CBS-APNO methods. Overall, our most accurate calculations provide an enthalpy of formation in the range of -26.2 to -26.7 kcal mol(-1), which is within computational error of the suggested experimental value. The relative merits of each of the three computational methods are discussed and depend upon the accuracy of experimental enthalpies of formation required in the calculations and the importance of systematic computational errors in the work reaction. Our results also calculate Delta(f) H(o)(298) for the formyl anion (HCO(-)) as 1.28+/-0.43 kcal mol(-1).     

Molecular structure,conformational mobility,vibrational spectra,and thermochemistry of peroxyacetic acid: an ab initio and density functional study

The structure of the peroxyacetic acid (PAA) molecule and its conformational mobility under rotation about the peroxide bond was studied by ab initio and density functional methods. The free rotation is hindered by the trans-barrier of height 22.3 kJ mol^–1. The equilibrium molecular structure of AcOOH (C _s symmetry) is a result of intramolecular hydrogen bond. The high energy of hydrogen bonding (46 kJ mol^–1 according to natural bonding orbital analysis) hampers formation of intermolecular associates of AcOOH in the gas and liquid phases. The standard enthalpies of formation for AcOOH (–353.2 kJ mol^–1) and products of radical decomposition of the peroxide — AcO^· (–190.2 kJ mol^–1) and AcOO^· (–153.4 kJ mol^–1) — were determined by the G2 and G2(MP2) composite methods. The O—H and O—O bonds in the PAA molecule (bond energies are 417.8 and 202.3 kJ mol^–1, respectively) are much stronger than in alkyl hydroperoxide molecules. This provides an explanation for substantial contribution of non-radical channels of the decomposition of peroxyacetic acid. The electron density distribution and gas-phase acidity of PAA were determined. The transition states of the ethylene and cyclohexene epoxidation reactions were located (E _a = 71.7 and 50.9 kJ mol^–1 respectively).