Theoretical Study on Intermolecular Interactions and Thermodynamic Properties of Dimethylnitroamine Clusters

Ab initio SCF and Mφller-Plesset correlation correction methods in combination with counterpose procedure for BSSE correction have been applied to the theroetical studying of dimethylnitroamine and its dimers and trimers.Three optimized stable dimers and two trimers have been obtained.The corrected binding energies of the most stable dimer and trimer were predicted to be -24.68kJ/mol and -47.27kJ/mol,respectively at the MP2/6-31G^*//HF/6-31G^* level.The proportion of correlated interation energies to their total interaction energies for all clusters was at least 29.3 percent,and the BSSE of ΔE(MP2) was at least 10.0kJ/mol.Dispersion and/or electrostatic force were dominant in all clusters.There exist cooperative effects in both the chain and the cyclic trimers.The vibrational frequencies associated with N-O stretches or wags exhibit slight red shifts,but the modes associated with the motion of hydrogen atoms of the methyl group show somewhat blue shifts with respect to those of monomer.Thermodynamic properties of dimethylnitroamine and its clusters at different temperatures have been calculated on the basis of vibrational analyses.The changes of the Gibbs free energies for the aggregation from monomer to the most stable dimer and trimer were predicted to be 14.37kJ/mol and 30.40kJ/mol,respectively,at 1 atm and 298.15K.     

Pi-pi interaction in pyridine

pi-pi Interaction in pyridine dimer and trimer has been investigated in different geometries and orientations at the ab initio (HF, MP2) and DFT (B3LYP) levels of theory using various basis sets (6-31G, 6-31G, 6-311++G) and corrected for basis set superposition error (BSSE). While the HF and DFT calculations show the pyridine dimer and the trimer to be unstable with respect to the monomer, the MP2 calculations show them to be clearly stable, thus emphasizing the need to include electron correlation while determining stacking interaction in such systems. The calculated MP2/6-311++G binding energy (100% BSSE corrected) of the parallel-sandwich, antiparallel-sandwich, parallel-displaced, antiparallel-displaced, T-up and T-down geometries for pyridine dimer are 1.53, 3.05, 2.39, 3.97, 1.91, 1.47 kcal/mol, respectively. The results show the antiparallel-displaced geometry to be the most stable. The binding energies for the trimer in parallel-sandwich, antiparallel-sandwich, and antiparallel-displaced geometry are found to be 3.18, 6.14, and 8.04 kcal/mol, respectively.     

Theoretical Study on the Intermolecular Interactions of Tetrazole Dimers

1 INTRODUCTION Tetrazole and its derivatives are widely applied in the fields of agriculture, biology, chemistry, phar- macology and photographic technology, and they play significant roles in the science and technology as well as national defence[1]. In the past, the res- earches were focused on the molecular geometries, electronic structures, IR, thermodynamic properties, tautomerization, pyrogenation and sensitivity of tetrazole compounds[1～5]. However, study of tetra- zole dimers ha…     

A theoretical study on the intermolecular interaction of energetic system-Nitromethane dimer

Three optimized geometries of nitromethane dimer have been obtained at the HF/6-31G level.Dimer binding energies have been corrected for the basis set superposition error (BSSE) and the zero point energy.Computed results indicate that the cyclic structure of (CH3NO2)2 is the most stable of three optimized geometries,whose corrected binding energyis 17.29 kJ mol-1 at the MP4SDTQ/6-31G//HF/6-31G level.In the optimized structures of nitromethane dimer,the inter-molecular hydrogen bond has not been found; and the charge-transfer interaction between CH3NO2 subsystems is weak; and the correlation interaction energy makes a little contribution to the intermolecular interaction energy of the dimer.     

Theoretical study on intermolecular interaction of epoxyethane dimer

Ab initio calculations at Hartree–Fock and fourth‐order Mø ller–Plesset (MP4) correlation correction levels with 6‐31G* basis set have been performed on the epoxyethane dimer. Dimer binding energies have been corrected for the basis set superposition error (BSSE) and the zero‐point energy. The greatest corrected dimer binding energy is −8.36 kJ/mol at the MP4/6‐31G*//HF/6‐31G* level. The natural bond orbital analysis has been performed to trace the origin of the weak interactions that stabilize dimer. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 94–98, 2000     

Ab initio Study on the Intermolecular Interaction and Thermodynamic Properties of Methyl Nitrate Dimer

Three stable dimers of methyl nitrate have been obtained and their geometries have been fully optimized at the HF/6‐31G,. level. Binding energies have been calculated with correction for the basis set superposition error (BSSE) and zero point energy (ZPE). The cyclic overlap‐type structure, the binding energy of which is 11.97 kJ/mol at the MP4SDTQ/6‐31G. / HF/6‐31G. level, is the most stable. No intermolecular hydrogen bond was found, and the charge transfer between two subsystems is minute. The thermodynamic properties of methyl nitrate and its dimers have been calculated based on the vibrational analysis and statistical thermodynamics.     

硝仿肼离子对相互作用的密度泛函理论研究

用密度泛函理论(DFT)方法,在B3LYP/6-31+G^**水平下,求得硝仿肼离子对体系势能面上2种全优化构型.经基组叠加误差(BSSE)和零点能校正,求得离子对最大相互作用能为-420.03kJ/mol,肼和硝仿离子化所需能量可由该值得到完全补偿.离子对间键的主要贡献为库仑作用,但键鞍点上的电子密度值表明共价作用也有显著的贡献.基于统计热力学求得相关体系的热力学性质,298.2K时由自由离子形成最稳定离子对的最大焓变和最大自由能变化分别为-419.72和-376.61kJ/mol     

An ab initio study of intermolecular interactions of nitromethane dimer and nitromethane trimer

Different geometries of nitromethane dimer and nitromethane trimer have been fully optimized employing the density functional theory B3LYP method and the 6-31++G** basis set. Three-body interaction energy has been obtained with the ab initio supermolecular approach at the levels of MP2/6-31++G**//B3LYP/6-31++G** and MP2/aug-cc-pVDZ//B3LYP/6-31++G**. The internal rotation of methyl group induced by intermolecular interaction has been observed theoretically. For the optimized structures of nitromethane dimer, the strength of C--H...O--N H-bond ranges from -9.0 to -12.4 kJ mol(-1) at the MP2/aug-cc-pVDZ//B3LYP/6-31++G** level, and the B3LYP method underestimates the interaction strength compared with the MP2 method, while MP2/6-31++G**//B3LYP/6-31++G** calculated DeltaE(C) is within 2.5 kJ mol(-1) of the corresponding value at the MP4(SDTQ)/6-31G**//B3LYP/6-31++G** level. The analytic atom-atom intermolecular potential has been successfully regressed by using the MP2/6-31++G**//B3LYP/6-31++G** calculated interaction energies of nitromethane dimer. For the optimized structures of nitromethane trimer the three-body interaction energies occupy small percentage of corresponding total binding energies, but become important for the compressed nitromethane explosive. In addition, it has been discovered that the three-body interaction energy in the cyclic nitromethane trimer is more and more negative as intermolecular distances decrease from 2.2 to 1.7 A.     

硝酸乙酯分子间相互作用的ab initio研究

在abinitio-HF/6-31G水平上求得硝酸乙酯二聚体势能面上的四种优化构型和电子结构。经MP2电子相关校正和基组叠加误差(BSSE)以及零点能(ZPE)校正，求得二聚体的最大结合能为11.46kJ.mol^-^1，还进行HF/6-311G和HF/6-311++G水平的总能量比较计算，发现6-31G基组对计算结合能比较适合，二子体系间的电荷转移很少，对优化构型进行振动分析，并基于统计热力学求得从单体形成二聚体的热力学性质变化。     

叠氮乙烷二聚体分子间相互作用的理论研究

Energetic materials are aggregative and mixed systems. The intermolecular interactions play significantroles in the physical,chemical and explosive property. The study on intermolecular interactions of energetic materials has attracted wide attention. The organic azides are an important category of energetic materials and widely used in many fields. Ethyl azide is the simple model having the explosive property for the organic azides energetic compound. Ethyl azide monomer（Ⅰ）and all its possible stable clusters（Ⅱ,Ⅲ and Ⅳ）are fully optimized by ab initio method at the HF/6-311++G** level. Vibrational frequencies calculated to ascertain each structure are characterized to be the stable structure（no imaginary frequencies）. The proportions of correlated interaction energies to their total interaction energies ΔE（MP2）are 65.14%,63.76% and 65.62% for Ⅱ,Ⅲ and Ⅳ respectively. In addition,the basis set superposition error（BSSE）correction energies are 7.82,7.61 and 4.40 kJ/mol for Ⅱ,Ⅲ and Ⅳ respectively. The zero point energy （ZPE） corrections for the interaction energies are much less than those of MP2 electron correlation and BSSE correction energies. After MP2 electron correlation correction,BSSE and ZPE correction,the greatest corrected intermolecular interaction of the dimers is -10.45 kJ/mol. The charge redistribution mainly occurs on the adjacent N?H atoms between submolecules. The charge transfer between two subsystems is very small. Natural bond orbital（NBO）analysis is performed to reveal the origin of the interaction. Based on the statistical thermodynamic method,the standard thermodynamic functions,heat capacities（C0p）,entropies（S0m）and enthalpies（H0m）and the changes of thermodynamic properties from the monomer to dimer with the temperatures ranging from 200. 00 K to 800. 00 K have been obtained.     

Ab initio Studies on Intermolecular Interaction of Formamide and Hydroxyacetonitrile Dimers

The structures, the binding energies and the thermodynamic properties of formamide and hydroxyacetonitrile(HAN) dimers have been studied by means of the self-consistent ab initio Hartree-Fock and the second-order Mφller-Plesset correlation energy correction methods. The counterpoise procedure was used to check the basis set superposition error(BSSE) of the binding energies. There exist cyclic structures in a formamide dimer(Ⅰ), a HAN dimer(Ⅱ) and their heterodimer(Ⅲ). The corrected binding energies for dimers Ⅰ, Ⅱ and Ⅲ are respectively -45.53, -45.83 and -43.89 kJ/mol at the MP2/aug-cc-p VDZ//HF/aug-cc-p VDZ level. The change of the Gibbs free energies(ΔG) in the process of Ⅰ Ⅱ→2Ⅲ was predicted to be -2.74 kJ/mol at 298.15 K. Dimer Ⅲ can be spontaneously produced in the mixture of formamide and HAN, which is in agreement with the experimental fact that most cyanohydrins are capable of interacting with dipeptide cyclo-His-Phe(CHP).     

A density-functional theory investigation of 3-nitro-1,2,4-triazole-5-one dimers and crystal

Density-functional method with different basis sets was applied to the study of the highly efficient and low sensitive explosive 3-nitro-1,2,4-triazole-5-one (NTO) in both gaseous dimer and its bulk state. The binding energies have been corrected for the basis set superposition errors. Six stable dimers (II-VII) were located. The corrected binding energy of the most stable dimer VII is predicted to be -53.66 kJ/mol at the B3LYP/6-311++G(**) level. It was found that the structures of the more stable dimers (V-VII) are through the hydrogen bonding interaction between the carbonyl oxygen and the azole hydrogen of 3-nitro-1,2,4-triazole-5-one. The changes of Gibbs free energies (DeltaG) in the processes from the monomer to the dimers at 298.15 K are 8.51, 0.90, 0.35, -8.74, -10.67, and -11.06 kJ/mol for dimers from II to VII, respectively. Dimers V-VII, possessing cyclic structures, can be spontaneously produced from the isolated monomer at room temperature. The lattice energy is -156.14 kJ/mol, and this value becomes to -150.43 kJ/mol when a 50% correction of the basis set superposition error was adopted. The frontier bands are quite flat. Judged from the value of band gap of 4.0 eV, it may be predicted that 3-nitro-1,2,4-triazole-5-one is an insulator. Most atoms in NTO, with the exception of C(5) atom and the nitro atoms, make up the upper valence bands. In contrast, the lower conduction bands mainly consist of the nitro N and O atoms. The population of the C-NO(2) bond is much less than those of the other bonds and the detonation may be initiated by the breakdown of this bond.     

NTO二聚体分子间相互作用的理论研究

在DFT-B3LYP/6-311＋＋G**水平上求得NTO二聚体势能面上六种优化构型和电子结构. 经基组叠加误差(BSSE)和零点能(ZPE)校正, 求得分子间最大相互作用能为－53.66 kJ/mol. 二子体系间的电荷转移很少. 由自然键轨道分析揭示了相互作用的本质. 对优化构型进行振动分析, 并基于统计热力学求得200.0～800.0 K温度范围从单体形成二聚体的热力学性质变化. 发现二聚主要由强氢键所贡献, 但结合能大小并不为氢键所完全决定. 二聚过程在较低温度或常温下能自发进行.     

Theoretical Studies on Intermolecular Interactions of 4-Amino-5-nitro-1,2,3-triazole Dimers

1 INTRODUCTION Triazole, a five-membered heterocyclic compound with three nitrogen atoms, is an important interme- diate product of medicine and chemical industry as well as insecticide [1]. Due to its small volume and high nitrogenous density, triazole holds more and more attraction for the material researchers, espe- cially the researchers of high-energy insensitive explosive. It is reported that its nitro and amino deri- vatives are a sort of important high-energy mate- rials[2]. Previ…     

A quantum-chemical study of the LiH + LiH⋅− ⇄ LiH2− + Li⋅ reaction

Parts of the potential energy surface of the title process and related processes have been investigated at the SCF /6-31G **, SCF /6-31++G **, and MP 2/6-31++G ** levels. The investigated reaction is exothermic (?6.23 kcal/mol, MP 4/6-31++G **//MP 2/6–31++G** level, ZPE included): A linear intermediate radical anion, Li? H? Li? H??, is significantly stabilized with respect to LiH + LiH?? (?38.74 kcal/mol, the same level as above). The BSSE at MP 2/6–31++G **//MP 2/6–31++G ** amounts to 1.8 kcal/mol. The title process seems to be suitable for experimental study in molecular beams.     

Blue-shifting hydrogen bond in the benzene-benzene and benzene-naphthalene complexes

Ab initio complete optimizations at MP2/6-31++G** level have been performed in the T-shaped geometry of the benzene-benzene and benzene-naphthalene complexes. To check the effect of the basis set superposition error (BSSE), optimizations have been done in the BSSE corrected and BSSE uncorrected potential energy surfaces. The BSSE effect in the calculation of the Hessian has also been evaluated to check its influence in the frequency values. Quantum theory atoms in molecules (QTAIM) calculations have also been performed on both dimers. Intermolecular energies differ around a 25% when the optimization is performed with or without counterpoise corrected gradients. The influence of BSSE is also noticeable in the distances. Frequency shifts show big changes because of the BSSE. Thus, uncorrected values are up 350% larger than corrected ones. The hypotheses given in the literature to explain the origin of the blue-shifting hydrogen bond do not seem to give a suitable explanation for all characteristics of the behavior found in the studied systems.     

Ab initio molecular orbital calculations of the infrared spectra of hydrogen-bonded complexes of water,ammonia and hydroxylamine

Summary The geometries of three hydrogen-bonded dimers of hydroxylamine have been optimized, at the MP2 level of theory, using the 6-31G** basis set. These calculations yielded three separate local minima on the dimer potential energy surface. The interaction energies of these three species have been calculated, and corrected for basis set superposition error. The infrared band wavenumbers and intensities have been computed, and the monomer-dimer wavenumber shifts and intensity enhancements rationalized in terms of the types and strengths of hydrogen bonds present. The predicted wavenumbers have been correlated with those measured in a recent matrix isolation spectroscopic study, and an argument for the structure of the preferred dimer has been presented.     

Rapid evaluation of the binding energies in hydrogen-bonded amide-thymine and amide-uracil dimers in gas phase

The binding energies and the equilibrium hydrogen bond distances as well as the potential energy curves of 48 hydrogen‐bonded amide–thymine and amide–uracil dimers are evaluated from the analytic potential energy function established in our lab recently. The calculation results show that the potential energy curves obtained from the analytic potential energy function are in good agreement with those obtained from MP2/6‐311+G** calculations by including the BSSE correction. For all the 48 dimers, the analytic potential energy function yields the binding energies of the MP2/6‐311+G** with BSSE correction within the error limits of 0.50 kcal/mol for 46 dimers, only two differences are larger than 0.50 kcal/mol and the largest one is only 0.60 kcal/mol. The analytic potential energy function produces the equilibrium hydrogen bond distances of the MP2/6‐311+G** with BSSE correction within the error limits of 0.050 Å for all the 48 dimers. The analytic potential energy function is further applied to four more complicated hydrogen‐bonded amide–base systems involving amino acid side chain and β‐sheet. The values of the binding energies and equilibrium hydrogen bond distances obtained from the analytic potential energy function are also in good agreement with those obtained from MP2 calculations with the BSSE correction. These results demonstrate that the analytic potential energy function can be used to evaluate the binding energies in hydrogen‐bonded amide–base dimers quickly and accurately. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Intermolecular Interaction of HMX： an Application of ONIOM Methodology

IntroductionExtensive studies on intermolecular interac-tions have been made in the past decades due totheir importance in a wide range of physical,chem-ical and biological fields.Researches on the weakintermolecular interactions began with hydrogenbonds.Scheiner summarized the ab initio investiga-tions on hydrogen bonding in detail[1] .With the abinitio method supermolecular structures and bind-ing energies can be predicted notonly for H- bondedsystems but also for other systems[2 _ 5] when …     

Conformers and intramolecular hydrogen bonding of the oxalic acid monomer and its anions

Density functional theory, B3LYP/6‐31G** and B3LYP/6‐311+G(2d,p), and ab initio MP2/6‐31G** calculations have been carried out to investigate the conformers, transition states, and energy barriers of the conformational processes of oxalic acid and its anions. QCISD/6‐31G** geometrical optimization is also performed in the stable forms. Its calculated energy differences between the two most stable conformers are very near to the related observed value at 7.0 kJ/mol. It is found that the structures and relative energies of oxalic acid conformers predicted by these methods show similar results, and that the conformer L1 (C_2h) with the double‐interfunctional‐groups hydrogen bonds is the most stable conformer. The magnitude of hydrogen bond energies depends on the energy differences of various optimized structures. The hydrogen bond energies will be about 32 kJ/mol for interfunctional groups, 17 kJ/mol for weak interfunctional groups, 24 kJ/mol for intra‐COOH in (COOH)₂, and 60 kJ/mol for interfunctional groups in (COOH)COO⁻¹ ion if calculated using the B3LYP/6‐311+G(2d,p) method. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 541–551, 2000