Molecular Dynamics Simulation of Methane Hydrate Decomposition in the Presence of Alcohol Additives

The decomposition process of methane hydrate in pure water and methanol aqueous solution was studied by molecular dynamics simulation. The effects of temperature and pressure on hydrate structure and decomposition rate are discussed. The results show that decreasing pressure and increasing temperature can significantly enhance the decomposition rate of hydrate. After adding a small amount of methanol molecules, bubbles with a diameter of about 2 nm are formed, and the methanol molecules are mainly distributed at the gas-liquid interface, which greatly accelerates the decomposition rate and gas-liquid separation efficiency. The radial distribution function and sequence parameter analysis show that the water molecules of the undecomposed hydrate with ordered ice-like configuration at a temperature of 275 K evolve gradually into a long-range disordered liquid structure in the dynamic relaxation process. It was found that at temperatures above 280 K and pressures between 10 atm and 100 atm, the pressure has no significant effect on hydrate decomposition rate, but when the pressure is reduced to 1 atm, the decomposition rate increases sharply. These findings provided a theoretical insight for the industrial exploitation of hydrates.     

过氧化氢水溶液作用下甲烷水合物分解特性的分子动力学模拟研究

采用分子动力学模拟方法研究过氧化氢水(HP)溶液作用下结构I型(SI)甲烷水合物晶体分解特性. 系统分析甲烷水合物在过氧化氢水溶液作用下由晶态向液态转变过程的机理, 对比相同摩尔浓度乙二醇(EG)溶液作用下甲烷水合物分解变化规律, 得出HP与水合物热力学抑制剂EG一样对甲烷水合物分解具有促进作用, 为HP溶液促进甲烷水合物分解实验研究提供参考.     

不同浓度聚乙烯醇对甲烷水合物分解作用的分子动力学模拟

采用分子动力学方法,模拟了273.15K下聚乙烯醇(PVA)对甲烷水合物的分解作用.研究发现,PVA浓度为2.7wt%时,水分子始终在其平衡位置附近波动,扩散系数仅为1.04×10-11m2/s;PVA浓度为5.2wt%时,水合物笼型结构坍塌,水分子以液态水的形式存在,甲烷分子从孔穴中逸出,聚乙烯醇的羟基在分子内部形成氢键,形成团簇,产生空间位阻,阻止了水分子再生成水合物,水分子的扩散系数1.61×10-9m2/s;PVA浓度为7.6wt%时,甲烷水合物周围有部分笼型结构被破坏,部分甲烷分子从孔穴中逸出,水分子扩散系数为3.55×10-10m2/s.得出聚乙烯醇对甲烷水合物的分解作用大小为:5.2wt%7.6wt%2.7wt%,为PVA溶液促进甲烷水合物分解实验研究提供参考.     

热力学抑制剂作用下甲烷水合物分解过程的分子动力学模拟

采用正则系综(NVT)分子动力学方法模拟研究277.0 K、11.45 mol·L-1的热力学抑制剂乙二醇(EG)溶液作用下甲烷水合物分解微观过程. 模拟显示甲烷水合物的分解从甲烷水合物固体表面开始, 逐渐向内部推移, 固态水合物在分解过程中逐渐缩小, 直至消失. 固态水合物的分解从晶格扭曲变形开始, 之后笼形框架结构破裂, 最后形成笼形结构碎片. 同时已经分解的甲烷水合物在外层形成水膜, 包裹里层正在分解的甲烷水合物, 增大里层甲烷水合物分解传质阻力.     

用分子动力学模拟水合物储氢

用分子动力学(MD)模拟方法系统研究了结构Ⅰ型(SⅠ)和结构H型(SH)氢气水合物中氢气的占据情况并确定了氢气水合物的稳定结构: SⅠ水合物氢气分子数小胞中为2, 大胞中为3; SH水合物氢气分子数小胞中为2, 中胞中为2, 大胞中为11. 分析了稳定情况下水合物各胞腔内氢气分子之间的径向分布函数(RDF), 得出了氢气分子在各胞腔内的稳定位置. 由稳定位置得到了稳定结构下氢气水合物的储氢质量分数: SⅠ为5.085%, SH为6.467%. 与实验对比得出结论: SH水合物稳定结构下的储氢能力最强.     

锂-,钠-,钾水化蒙脱石层间结构的分子动力学模拟

运用分子动力学(molecular dynamics, MD)方法分别研究了含有32, 64和96个水分子的Li-, Na-, K-蒙脱石层间阳离子与水分子的位置和结构. 计算结果表明蒙脱石层间阳离子位置与四面体和八面体电荷位置及离子的大小有关. 一层水合物中可以观察到三种阳离子都能和四面体电荷与八面体电荷位置分别形成内、外配位作用. 二层水合物中, 仍然可以观察到Li^＋和Na^＋与电荷位置的配位作用, 但是已经开始向层中其他方向扩散, 而K^＋仍然在粘土的表面附近. 三层水合物中, Li^＋, Na^＋开始从电荷位置和表面分离, K^＋也开始向层间其他方向扩散. 水分子在所有三种水合物中都分散于层间各个方向. 径向分布函数的分析结果表明层间三种阳离子组织水分子的能力不同, 水化作用随着阳离子半径的增大而减弱; 此外层中水分子的聚合程度随着水分子的增加而加强, 水分子的结构也不同于模拟的液体水分子的结构; 说明蒙脱石层间阳离子的溶剂化作用对水分子的组织起着重要的作用.     

用分子动力学模拟天然气水合物的抑制效应

用分子动力学模拟方法确定了结构H型(SH)天然气水合物的稳定晶体生长面为(001), 系统研究了277 K时三种动力学抑制剂对此晶面的影响. 模拟显示抑制剂中的氧与表面水分子形成氢键, 从而破坏原有的稳定结构, 造成水合物笼型结构坍塌, 达到抑制水合物形成的效果. 比较三种不同动力学抑制剂对SH的抑制效果得出: PVCap＞PEO＞PVP. 在此基础上研究了PVCap对天然气水合物结构I型(SI), 结构II型(SII)和SH三种不同晶型的抑制效应. 模拟发现抑制效果的次序为: SH＞SI＞SII.     

聚乙烯唑啉作用下甲烷水合物分解的分子动力学模拟

利用分子动力学模拟系统研究了不同质量浓度下(1.25%、2.50%、6.06%)聚乙烯唑啉(PEtO)对甲烷水合物的分解作用. 模拟体系为甲烷水合物2′2′2的超胞和聚合物对接体系. 模拟发现水分子间氢键构架的水合物笼型结构在PEtO的作用下出现扭曲, 最终导致水合物笼型结构完全坍塌. 通过氧原子径向分布函数、均方位移以及扩散系数比较不同浓度PEtO的作用, 证实在一定浓度范围内, PEtO的浓度越高, 其水合物分解作用越强. 此外, PEtO 具有一定的可生物降解性. PEtO 对水合物的作用为: PEtO 吸附在水合物表面, 其中的酰胺基(N―C＝O)与成笼的水分子形成氢键, 破坏邻近的笼形结构, 令水合物分解; PEtO不断分解表面的水合物, 直到水合物笼完全分解.     

Reactive Molecular Dynamics Simulation on Thermal Decomposition of n-Heptane

The thermal decomposition of n-heptane is an important process in petroleum industry. The theoretical investigations show that the main products are C₂H₄, H₂, CH₄, and C₃H₆, which agree well with the experimental results. The products populations depend strongly on the temperature. The quantity of ethylene increases quickly as the temperature goes up. The conversion of n-heptane and the mole fraction of primary products from reactive molecular dynamic and chemical kinetic modeling are compared with each other. We also investigated the pre-exponential factor and activation energy for thermal decomposition of n-heptane by kinetic analysis from the reactive force field simulations, which were extracted to be 1.78×10¹⁴ s^-1 and 47.32 kcal/mol respectively.     

分子动力学模拟无定形BCN体系结构特征

为研究无定形BCN材料的原子结构特征, 采用分子动力学方法模拟了高温下无定形BCN体系的动力学行为, 计算并分析了引入C原子对体系的径向分布函数(RDF)和配位数的影响. 模拟结果表明, C原子对BCN体系的RDF曲线的峰位置及形状影响很小, 但使其偏径向分布函数(PRDF)的一些峰向右偏移; 引入的C原子部分占据了原来N原子的位置, 使得B-N的配位数降低. 在模拟条件下, 未观察到BN相与C相分离.     

分子动力学模拟在聚合物热解中的应用

分子动力学模拟作为分子模拟的重要分支已经在化学、化工、材料、生物等领域受到了广泛的关注。介绍了分子动力学模拟的基本原理,阐述了分子动力学模拟在高分子聚合物热解反应机理研究中的应用。实例表明:在研究物质化学反应机理方面,分子动力学模拟是一种有效的研究手段。     

Use of Electrical Resistance to Detect the Formation and Decomposition of Methane Hydrate

The changes of electrical resistance(R)were studied experimentally in the process of CH_4 hydrate formation and decomposition,using temperature and pressure as the auxiliary detecting methods simultaneously.The experiment results show that R increases with hydrate formation and decreases with hydrate decompositon.R is more sensitive to hydrate formation and decompositon than temperature or pressure,which indicates that the detection of R will be an effective means for detecting natural gas hydrate(NGH)quantitatively.     

Apicidin选择性抑制ClassⅠ HDACs分子动力学研究

采用模拟方法研究组蛋白脱乙酰酶抑制剂(Apicidin)选择性抑制组蛋白去乙酰化酶(Histone deacetylases, HDACs)中的HDAC1和HDAC8. 通过HDAC8晶体结构同源模建HDAC1三维结构模型, 将Apicidin分别与HDAC1和HDAC8对接并进行分子动力学模拟, 结果表明, HDAC1活性口袋入口处的Arg270是Apicidin-HDAC1形成稳定结构的重要因素; HDAC1中Tyr303及His178与Apicidin形成2个持续存在的氢键, 而在HDAC8中未发现, 这是Apicidin选择性抑制HDAC1高于HDAC8的另一重要原因.     

A Refined Intermolecular Interaction Potential for Methane: Spectral Analysis and Molecular Dynamics Simulations

The previously constructed methane interaction potential energy surface calculated at the second‐order Møller‐Plesset (MP2) perturbation theory has been significantly improved in two aspects. First, all ab initio potential energy data are calculated by the supermolecule counterpoise corrected coupled cluster with single and double and perturbative triple excitations [CCSD(T)] method with Dunning’s correlation‐consistent aug‐cc‐pVXZ, X=D, T, Q, 5, basis sets and extrapolated to the complete basis set (CBS) limits with a convergence precision of 0.01 kcal/mol. Second, instead of the simple 4‐site model proposed in the previous study, a 5‐site model has been used to represent the ab initio potential data. The simulated infrared spectrum using the potential energy surface seems to be broadly in line with the spectral features observed in experiments. Molecular dynamics simulations using the ab initio force field show quantitative agreements with experiments. The properties examined in this paper include the atom‐to‐atom radial distribution functions in liquid and supercritical phases and the self‐diffusion coefficients over a wide range of thermodynamic conditions. It is shown that the refined ab initio force field can be applied to study fluid properties in different phases.     

金纳米颗粒周围水的结构和动力学性质的分子动力学模拟

采用经典的分子动力学模拟方法系统地研究了在常温条件下金纳米颗粒周围水的结构与动力学性质. 结果表明, 水分子在纳米颗粒附近形成了明显的多层结构. 同时随着径向距离的减小, 水分子的空间取向也从无序排列趋向于有序排列. 通过分析界面处不同水层中的均方位移及停留时间分布, 发现紧贴颗粒表面的第一和第二水层中的水分子表现出很低的扩散系数, 而第三和第四水层中的水分子则能够轻易地离开界面区域而进入主体相区域. 此外, 在界面处的每个水分子的氢键平均数要高于在主体相的平均值.     

微波场中乙烷及丙烷气体水合物的分解特性

研究了2.45GHz微波场中I型乙烷水合物及II型丙烷水合物的热激分解过程,基于晶体表面两步分解机制的动力学模型,结合传热传质分析了其分解特性.结果表明:水合物在微波场中的加热分解是一个与实际微波电磁场相互耦合的过程,微波体积加热的特点强化了水合物颗粒表层的传热传质过程,时间累积的热效应增大了水合物晶体破解速率;在120至540W入射功率下,乙烷、丙烷水合物气化速率分别达到0.109-0.400mol·min-·1L-1及0.090-0.222mol·min-1·L-1.在一定范围内增大微波功率可显著提高水合物分解速率,其中乙烷水合物一直处于功率主控区,丙烷水合物更早进入功率和分解动力机制共同控制区.     

硝酸钾电解质溶液水化结构的分子动力学模拟

Molecular dynamics simulations were carried out to study the structure of ion clusters and hydration properties of KNO3 solution. The water molecule was treated as a simple-point-charge (SPC) model, and a four-site model for the nitrate ion was adopted. Both the Coulomb and Lennard-Jones interactions between all the charged sites were considered, and the long-range Coulomb electrostatic interaction was treated using Ewald summation techniques. The configuration of ionic pairs, the radial distribution function of the solution, and the effect of solution concentration on ionic hydration were studied in detail. It was found that there are ionic association phenomena in KNO3 solution and that the dimeric, triplet, solvent-separated ion pairs, and other complex clusters can be observed at high ionic concentration condition. As the concentration of solution decreases, the ionic hydration number increases, 5-7 for cation K+ and 3.5-4.7 for anion NO3-, which is in good agreement with former Monte Carlo and time-of-flight neutron diffraction results.     

LaCl3-KCl熔体结构的分子动力学研究

用分子动力学计算机模拟方法研究了LaCl3-KCl熔体的结构和输运性质, 获得了熔体的偏径向分布函数、配位数、键角分布及均方位移等信息. 计算结果表明, 熔体中存在变形的八面体LaCl63-离子. K 和Cl-离子是熔体电流的主要携带迁移者, 而LaCl3浓度对熔体结构有较大的影响.     

Simulation by Molecular Dynamics of Erbium-Activated Silica-Titania Glasses

Rare-earth doped silicate-based glasses are widely used in telecommunication technology. A limitation in the performance of active optical devices such as amplifier comes from the rare-earth clustering. Simulation methods give complementary informations to the spectroscopic usual investigations. We present a molecular dynamics simulation of a SiO₂-TiO₂:Er³⁺ system in varying its composition. Different distribution functions have been analyzed in order to have information about the clustering of erbium. To this purpose, the titanium distribution has been studied for concentration 7.8 and 15.7% Ti/(Ti + Si). We have simulated the structure of the system doped with 1 and 2.3 mol%. A calculation of the crystal field strength for the different kinds of erbium site has been interpreted in the light of the local structure. The important trend of erbium for clustering in our modeled system has been explained by the energetic requirements of the rare-earth.     

采用分子动力学模拟方法评价人类VDAC通道蛋白晶体结构的生物活性

电压依赖阴离子选择性通道（Voltage dependent anion-selective channel, VDAC）是线粒体外膜上重要的通道蛋白,转运线粒体和细胞质之间的代谢物,对于线粒体发挥生理功能具有决定性作用. 为研究VDAC分子的调控机制,在电场存在和不存在的情况下,我们对I型人类VDAC分子（hVDAC1）分别进行了分子模拟研究. 比较结果显示：外加电场的有无与方向变化对hVDAC1分子的运动模式和离子通过过程影响不明显,hVDAC1分子仍然保持以N端α螺旋在β桶内横向运动为主的运动模式. 综合模拟结果和相关的实验结果,我们推测,发表的hVDAC1晶体结构可能不是其发挥生理功能的结构状态.