用分子动力学模拟甲烷水合物热激法分解

用分子动力学模拟方法研究甲烷水合物热激法分解，系统地研究注入340 K液态水的结构Ⅰ型甲烷水合物的分解机理.模拟显示水合物表层水分子与高温液态水分子接触获得热能，分子运动激烈，摆脱水分子间的氢键束缚，笼状结构被破坏.甲烷分子获得热能从笼中挣脱，向外体系扩散.热能通过分子碰撞从外层传递给内层水分子，水合物逐层分解.对比注入277K液态水体系模拟结果，得出热激法促进水合物分解. 关键词： 甲烷水合物 分子动力学模拟 热激法     

用分子动力学模拟甲烷水合物热激法结合化学试剂法分解

用分子动力学模拟方法研究甲烷水合物的热激法，化学试剂法，以及热激法结合化学试剂法分解，系统研究温度为277K和340K时添加液态水(WTR)和30wt％乙二醇(EG)溶液对水合物分解的影响.模拟显示WTR与水合物表面水分子形成氢键，破坏水合物原有的氢键平衡，造成笼状结构坍塌，水合物分解.EG分子中的羟基与水合物表面水分子形成氢键，从而破坏原有的稳定结构，造成水合物笼状结构被破坏，达到促进水合物分解，释放甲烷气体的效果.比较温度为277K和340K时添加WTR和30wt％EG溶液对水合物分解效果得出EG(340K)> WTR(340K)>EG(277K)>WTR(277K)，热激法结合化学试剂法能更好促进水合物分解.     

A study on dissociation of sII krypton hydrate and the effect of hydrocarbon guest molecules as stabilizer by molecular dynamics simulation

In this paper, the characteristics of structure II krypton hydrate are studied by molecular dynamics simulation under isobaric-isothermal (NPT) ensemble condition. The dissociation process of the hydrate is simulated and the effect of krypton (Kr) and various types of hydrocarbon guest molecules (HGMs) on the stability of the hydrate structure is investigated during the simulation time of 1 ns. The studied HGMs are propane, isobutane, neopentane, cyclopropane, cyclobutane, cyclopentane and cyclopentene. The structural change of the Kr-hydrate is analyzed with the radial distribution function, mean square displacement and diffusion coefficient. As temperature increases, the obtained results indicate a gradual increase in the Kr-hydrate cell size, which leads to distortion of the hydrate lattice and escaping of the encapsulated Kr molecules from the hydrate structure to form small bubbles of Kr aggregated in the aqueous solution.     

储氢笼型水合物生成促进机理的分子动力学模拟研究

用分子动力学(MD)模拟方法研究水合物法储氢的促进机理,系统研究纯H₂水合物、H₂+四氢呋喃(THF)水合物、H₂+四丁基溴化铵(TBAB)半笼型水合物和H₂+四异戊基溴化铵(TiAAB)半笼型水合物的微观结构及性质.模拟分析客体与笼子之间的稳定能ΔE_GH,得出水合物中大笼子对稳定水合物起到主要作用.THF进入大笼子能促进H₂水合物稳定,降低H₂水合物形成压力,模拟结果与实验一致.模拟对比不同客体在大笼子中的ΔE_GH值,得出从小到大的顺序依次为TiAAB,TBAB,THF,H₂.模拟结果表明半笼型水合物的稳定性比结构Ⅱ型水合物强,同时得出H₂+TiAAB半笼型水合物的结构最稳定.MD模拟为TiAAB成为一种水合物新型促进剂和新型储氢材料提供了理论依据. 关键词： 2笼型水合物')" href="#">H₂笼型水合物 分子动力学模拟 储氢 半笼型水合物     

Molecular dynamics simulation of decomposition and thermal conductivity of methane hydrate in porous media

The hydrate has characteristics of low thermal conductivity and temperature sensitivity. To further analysis the mechanism of thermal conductivity and provide method for the exploitation, transportation and utilization of hydrate, the effect of decomposition and thermal conductivity of methane hydrate in porous media has been studied by using the molecular dynamics simulation. In this study, the simulation is carried out under the condition of temperature 253.15 K-273.15 K and pressure 1 MPa. The results show that the thermal conductivity of methane hydrate increases with the increase of temperature and has a faster growth near freezing. With the addition of porous media, the thermal conductivity of the methane hydrate improves significantly. The methane hydrate-porous media system also has the characteristics of vitreous body.With the decrease of the pore size of the porous media, thermal conductivity of the system increases gradually at the same temperature. It can be ascertained that the porous media of different pore sizes have strengthened the role of the thermal conductivity of hydrates.     

Novel methodology for the calculation of the enthalpy of enclathration of methane hydrates using molecular dynamics simulations

Methane hydrates are encountered in a plethora of industrial and geological or environmental applications. In the current study, we present a novel methodology which is based on molecular dynamics simulations for the calculation of the enthalpy of enclathration of sI methane hydrates. Simulations are performed along the three-phase (Hydrate – Liquid water – Vapour; H–L_w–V) equilibrium line in the temperature range 274–310?K. The methodology takes into account the two different types of cages that are present in the sI methane hydrate and provides results for the enthalpy of enclathration for both types of cages, while it avoids performing calculations with the metastable, completely empty hydrate lattice. The formulation proposed is general and can be also applied to sII hydrates, while it can be modified/extended appropriately for use in the case of sH hydrates. Comparison is provided with available data from the literature and good agreement is observed.     

Effect of electrostatics techniques on the estimation of thermal conductivity via equilibrium molecular dynamics simulation: application to methane hydrate

Equilibrium molecular dynamics (MD) simulations for three system sizes of fully occupied methane hydrate have been performed at around 265 K to estimate the thermal conductivity using the Ewald, Lekner, reaction field, shifted-force and undamped Fennell–Gezelter methods. The TIP4P water model was used in conjunction with a fully atomistic methane potential with which it had been parameterized from quantum simulation. The thermal conductivity was evaluated by integration of the heat flux autocorrelation function (ACF) derived from the Green–Kubo formalism; this approach vas validated by estimation of the average phonon mean free path. The thermal conductivities predicted by non-periodic techniques were in reasonable agreement with the experimental results of 0.62 and 0.68 W/m K, although it was found that the estimates by the non-periodic techniques were up to 25% larger than those of Lekner and Ewald estimates, particularly for larger systems. The results for the Lekner method exhibited the least variation with respect to system size. A decomposition of the heat flux vector into its respective contributions revealed the importance of electrostatic interactions, and how different electrostatic treatments affect the contribution to the thermal conductivity.     

整体煤气化联合循环合成气水合物法分离CO2的分子动力学模拟

利用分子动力学（MD）模拟方法研究整体煤气化联合循环（IGCC）合成气（CO₂/H₂）水合物法分离CO₂的分离机理,系统研究了CO₂水合物、H₂水合物以及合成气水合物法一级分离所得CO₂/H₂混合气体水合物的微观结构及性质.模拟分析n个CO₂或H₂与水合物笼状结构的整体结合能ΔE关键词： 水合物法分离 分子动力学模拟 整体煤气化联合循环合成气 2分离')" href="#">CO₂分离     

Molecular dynamics simulations of pure methane and carbon dioxide hydrates: lattice constants and derivative properties

ABSTRACT

We report extensive molecular dynamics simulation results of pure methane and carbon dioxide hydrates at pressure and temperature conditions that are of interest to various practical applications. We focus on the calculation of the lattice constants of the two pure hydrates and their dependence on pressure and temperature. The calculated lattice constants are correlated using second order polynomials which are functions of either temperature or pressure. Finally, the obtained correlations are used in order to calculate two derivative properties, namely the isothermal compressibility and the isobaric thermal expansion coefficient. The current simulation results are also compared against reported experimental measurements and other simulation studies and good agreement is found for the case of isothermal compressibility. On the other hand, for the case of isobaric thermal expansion coefficient good agreement is found only with other simulation studies, while the simulation studies are in disagreement with experiments, particularly at low temperatures.     

Investigation of the structural and dynamic basis of kinesin dissociation from microtubule by atomistic molecular dynamics simulations

Kinesin is a molecular motor that can step processively on microtubules via the hydrolysis of ATP molecules. An important factor characterizing the processivity of the kinesin motor is its dissociation from the microtubule. Here, using all-atom molecular dynamics simulations, we studied the dissociation process of the kinesin head in weak-microtubule-binding or ADP state from tubulin on the basis of the available high-resolution structural data for the head and tubulin. By analyzing the simulated snapshots of the structure of the head-tubulin complex we provided detailed structural and dynamic information for the dissociation process. We found that the dissociation of the head along different directions relative to the tubulin exhibits very different dynamic behaviors. Moreover, the potential forms or energy landscapes of the interaction between the head and tubulin along different directions were determined. The studies have important implications for the detailed molecular mechanism of the dissociation of the kinesin motor and thus are critical to the mechanism of its processivity.     

CO_2水合物导热特性的分子动力学模拟

使用分子动力学模拟方法在NVT系综下对结构完整CO_2水合物以及结构缺陷CO_2水合物进行了导热模拟计算.对于结构完整的CO_2水合物,在200-230 K温度区间内,体系导热系数由0.4684 W·m~(-1)·K~(-1)变化到0.4836 W·m~(-1)·K~(-1),温度相关性较弱;而在230-280 K温度区间内,体系导热系数由0.4836 W·m~(-1)·K~(-1)变化到0.7494 W·m~(-1)·K~(-1),温度相关性变强;另外,通过计算功率图谱发现主体分子对水合物体系的导热贡献更大.对于结构缺陷CO_2水合物,发现晶穴占有率和笼形结构缺陷对体系导热均有一定影响,空笼晶胞导热系数约为完整晶胞导热系数的86.67%,体系的导热能力主要取决于主体结构的性质.     

碳硅二炔结构及性质分子动力学模拟研究

采用基于量子力学的半经验哈密顿量的计算方法,即SCED-LCAO方法,模拟研究了碳硅二炔的稳定性结构、成键特点、电子结构等性质. 得出其最稳定的结构是单层平面结构,晶格常数为12.251 Å. 它通过 含有两个Si-C三键的链连接六元环构成. 这种平面结构在很大高温范围内都可以保持其稳定特性,直到1520 K时,该基本结构才被破坏,且结构中出现四元环. 体系温度低于1520 K时,均可通过降温,恢复其零温时的结构. 研究还发现这种共轭结构中Si,C 原子间存在稳定的sp杂化形式,对分布函数得出其键长为1.58 Å左右. 高温时sp杂化逐渐转变成其他杂化形式. 计算结果表明,在零温下,该电中性系统中存在离域π键,使得系统中的Si-C键长呈现平均化趋势. 研究表明,碳硅二炔的能隙为1.416 eV,LUMO,HOMO能级分别是0.386 eV和–1.03 eV表明了其n型半导体特性. 关键词： 碳硅二炔 分子动力学模拟 sp杂化 稳定性     

二聚物在Cu表面上的扩散和解离研究

利用分子动力学模拟统计了几种不同温度下三种不同二聚物(Cu₂, Ag₂和Pd₂)在铜衬底(100), (111)表面上的扩散和解离行为, 探讨同质和异质二聚物在Cu表面上扩散和解离的特点; 采用分子动力学中的静态计算方法计算了这三种二聚物在扩散和解离过程中的能量势垒, 并与动力学模拟、二聚物与衬底的结合能等结果进行了比较, 探讨二聚物扩散和解离过程与扩散势垒、结合能、表面性质和温度等的关系. 原子间相互作用采用半经验EAM势. 结果表明: 同质和异质二聚物在各个不同表面上的扩散势垒、解离势垒有一定的规律, 并和二聚物与衬底的结合性质有关; 二聚物是否易解离与衬底表面的结构以及二聚物与衬底的结合性质关系密切; 二聚物解离前协同扩散的快慢与二聚物和衬底的结合性质以及二聚物在表面的扩散和解离势垒密切相关.     

Lattice dynamics study of low energy guest-host coupling in clathrate hydrate

Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P oxygen-shell model can accurately reproduce each peak position in the inelastic incoherent neutron scattering spectrum at the acoustic band （below 15 meV） and yield correct relative intensity. Based on the results, the uncertain profile at ～6 meV is assigned to anharmonic guest modes coupled strongly to small cages. Blue shift is proposed in phonon dispersion sheet in the case of anticrossing and found to be an evident signal for guest-host coupling that explains the anomalous thermal conductivity of clathrate hydrate.     

Lattice dynamics study of low energy guest--host coupling in clathrate hydrate

Our lattice dynamics simulation of Xe-hydrate with four-site TIP4P oxygen-shell model can accurately reproduce each peak position in the inelastic incoherent neutron scattering spectrum at the acoustic band (below 15\,meV) and yield correct relative intensity. Based on the results, the uncertain profile at $\sim $6\,meV is assigned to anharmonic guest modes coupled strongly to small cages. Blue shift is proposed in phonon dispersion sheet in the case of anticrossing and found to be an evident signal for guest--host coupling that explains the anomalous thermal conductivity of clathrate hydrate.     

CH4水合物生长速率影响因素的分子动力学模拟

采用分子动力学模拟,研究了温度、压力和电解质溶液对CH4水合物生长速率的影响.通过分析势能、均方位移、氢键数量、径向分布函数和四体结构有序参数,表征了CH4水合物的生长动力学.模拟结果表明,降低温度和提高压力可以显著提高CH4水合物的生长速率.当压力恒为15MPa,温度高于290K时,势能升高,CH4水合物晶体发生分解;温度由290K降至260K时,势能降低,CH4水合物持续生长.当温度恒为275K,压力由3MPa增至50MPa时,CH4水合物生长速率提高12%.此外,电解质离子的存在抑制了水合物的生长,电解质溶液浓度由1.5wt%增加到3.5wt%时, CH4水合物生长速率降低25%.     

Molecular dynamics study of mosaic structure in the Ni-based single-crystal superalloy

The mosaic structure in a Ni-based single-crystal superalloy is simulated by molecular dynamics using a potential employed in a modified analytic embedded atom method. From the calculated results we find that a closed three-dimensional misfit dislocation network, with index of $\langle 011\rangle${\{}100{\}} and the side length of the mesh 89.6\,{\AA}, is formed around a cuboidal $\gamma '$ precipitate. Comparing the simulation results of the different mosaic models, we find that the side length of the mesh only depends on the lattice parameters of the $\gamma $ and $\gamma '$ phases as well as the $\gamma $/$\gamma '$ interface direction, but is independent of the size and number of the cuboidal $\gamma '$ precipitate. The density of dislocations is inversely proportional to the size of the cuboidal $\gamma '$ precipitate, i.e.~the amount of the dislocation is proportional to the total area of the $\gamma $/$\gamma '$ interface, which may be used to explain the relation between the amount of the fine $\gamma '$ particles and the creep rupture life of the superalloy. In addition, the closed three-dimensional networks assembled with the misfit dislocations can play a significant role in improving the mechanical properties of superalloys.     

Molecular dynamics simulations of carbon dioxide hydrate growth in electrolyte solutions of NaCl and MgCl2

Molecular dynamics simulations are performed to study the growth of carbon dioxide (CO₂) hydrate in electrolyte solutions of NaCl and MgCl₂. The kinetic behaviour of the hydrate growth is examined in terms of cage content, density profile, and mobility of ions and water molecules, and how these properties are influenced by added NaCl and MgCl₂. Our simulation results show that both NaCl and MgCl₂ inhibit the CO₂ hydrate growth. With a same mole concentration or ion density, MgCl₂ exhibits stronger inhibition on the growth of CO₂ hydrate than NaCl does. The growth rate of the CO₂ hydrate in NaCl and MgCl₂ solutions decreases slightly with increasing pressure. During the simulations, the Na⁺, Mg²⁺, and Cl^? ions are mostly excluded by the growing interface front. We find that these ions decrease the mobility of their surrounding water molecules, and thus reduce the opportunity for these water molecules to form cage-like clusters toward hydrate formation. We also note that during the growth processes, several 5¹²6³ cages appear at the hydrate/solution interface, although they are finally transformed to tetrakaidecahedral (5¹²6²) cages. Structural defects consisting of one water molecule trapped in a cage with its hydrogen atoms being attracted by two Cl^? ions have also been observed.     

二元Lennard-Jones液体的相分离过程及其扩散性质的分子动力学研究

采用分子动力学(MD)模拟方法,研究了二元体系中相分离过程、粒子的扩散系数以及相分离域尺寸大小随温度的变化规律.发现,相分离域随温度的生长过程可以分为两个阶段,分别是温度比较高的快速生长阶段和低温时的稳定生长阶段;相分离体系中系统的扩散激活能不是常数,而是一个随温度变化的函数,并且当温度高于60 K时,满足关系式E(T)=a+bT^c.讨论了组元尺寸的变化对相分离过程的影响.结果表明,随两组元中某一组元 关键词： 相分离 扩散 分子动力学模拟     

聚酰亚胺/铜纳米颗粒复合物的分子动力学模拟研究

通过分子动力学模拟对聚酰亚胺/铜纳米颗粒复合物的形态结构、 热力学性质、力学特性进行计算, 分析其随模拟温度和纳米颗粒尺寸的变化规律. 模拟结果表明, 聚酰亚胺/铜纳米颗粒复合物为各向同性的无定形态结构, 铜纳米颗粒与聚酰亚胺基体之间通过较强的范德华作用结合在一起使结构更加稳定, 铜纳米颗粒表面多个原子层呈现无定形状态, 在铜颗粒和聚酰亚胺基体之间形成界面层, 界面区域随颗粒尺寸和温度的增加分别减小和增加. 聚酰亚胺/铜纳米颗粒复合物的等容热容随着颗粒尺寸增大而明显增高, 随温度变化比聚酰亚胺体系更为缓慢, 在较低温度下较小颗粒尺寸复合物的热容比聚酰亚胺体系更低. 聚酰亚胺/铜纳米颗粒复合物的热压力系数随颗粒尺寸增加而显著增大, 比聚酰亚胺体系的热压力系数更小, 且随温度升高而减小的程度要小得多. 聚酰亚胺/铜纳米颗粒复合物的热力学性质表现出明显的尺度效应, 温度稳定性明显高于聚酰亚胺体系. 聚酰亚胺/铜纳米颗粒复合物的力学特性表现出各向同性材料的弹性常数张量, 具有比聚酰亚胺体系更低的杨氏模量和泊松比, 随温度升高分别减小和增大, 与聚酰亚胺体系随温度的变化趋势相反, 且杨氏模量的温度稳定性显著提高, 同时泊松比随纳米颗粒尺寸增大而减小, 具有明显的尺度效应. 加入铜纳米颗粒形成复合物可获得与聚酰亚胺体系显著不同的力学新特性. 关键词： 分子动力学模拟 聚合物纳米复合物 聚酰亚胺 纳米颗粒