方阱链流体在固液界面分布的密度泛函理论研究

应用Yethiraj的加权密度近似泛函理论研究平板狭缝中方阱链流体的密度分布，系统的Helm holtz自由能泛函分为理想气体的贡献利剩余贡献两部分，其中剩余贡献部分分别采用刘洪 来等人建立的基于空穴相关函数的方阱链流体状态方程和Gil-Villegas等人提出的统计缔合 流体理论状态方程(SAFT-VR)结合简单加权密度近似计算.考察了不同链长、温度、系统密度 和壁面吸引强度下平板狭缝中方阱链流体的密度分布，并与Monte Carlo(MC)模拟结果进行 了比较.结果表明采用不同的状态方程对密度分布的计算有明显的影响，对于受限于硬壁狭 缝中的方阱链流体，温度和密度比较高时，两种状态方程计算的结果均与MC模拟符合得比较 好，在低温和低密度下效果变差，SAFT-VR方程的计算结果更接近于MC模拟结果.对于受限于 方阱壁狭缝中的方阱链流体，由于系统密度分布的非均匀性加强，采用两种状态方程计算的 结果均与MC模拟结果有一定偏差，寻找更合适的权重函数是进一步改进的关键. 关键词： 密度泛函理论 非均匀流体 密度分布 固液界面 方阱链     

平行板间方势阱偶极流体的结构性质研究

在密度泛函理论(DFT)框架下, 应用改进的基本度量理论(MFMT)表达硬球作用对自由能泛函的贡献, 根据统计力学理论结合加权密度近似(WDA)表达偶极作用对自由能泛函的贡献,得到了方势阱偶极流体在平行板间的密度分布表达式, 计算了偶极流体在两平行板间的密度分布, 并探讨了方势阱深度和宽度对体系密度分布的影响. 此外, 通过体系密度分布, 进一步分析了方势阱宽度和深度以及板间尺度与溶剂化力的关系.     

平行板间方势阱偶极流体的结构性质研究

在密度泛函理论(DFT)框架下, 应用改进的基本度量理论(MFMT)表达硬球作用对自由能泛函的贡献, 根据统计力学理论结合加权密度近似(WDA)表达偶极作用对自由能泛函的贡献,得到了方势阱偶极流体在平行板间的密度分布表达式, 计算了偶极流体在两平行板间的密度分布, 并探讨了方势阱深度和宽度对体系密度分布的影响. 此外, 通过体系密度分布, 进一步分析了方势阱宽度和深度以及板间尺度与溶剂化力的关系.     

扩展桥密度泛函近似于非匀一非硬球流体

为了将非匀一硬球流体的桥密度泛函近似扩展到非匀一非硬球流体,提出了一个理论方案．所得的LJ流体的密度泛函近似计算简单,精确．特别是密度泛函近似仅仅需要共存体相流体的二阶直接相关函数作为输入,因而可以应用于超临界与亚临界温度．所提出的理论方案可以认为是热力学理论的非匀一对应物．     

一个新的方阱流体状态方程

将方阱势能函数视为硬球势的一短程均匀负势的叠加,并由统计力学方法导出了相应的状态方程,这个方程包含两个定标的径向分布函数。利用已知的压缩因子分子动力学模拟数据,回归得到了这两个径向分布函数,从而建立了一个新的方肼流体状态方程。它的吸引项要比Alder等人回归得到的简单得多,与方阱流体压缩因子的MD数据一致性也更好,特别是在高密度区域。     

氮气在MCM-41中毛细凝聚的模拟和理论研究

采用巨正则系综 Monte Carlo 方法(GCMC)以及基于扩展基本度量理论和 MBWR 状态方程的密度泛函理论,研究了 77.4 K 时氮气在不同孔径的 MCM-41 分子筛中吸附的密度分布和吸附等温线.提出的平均场权重密度泛函理论,克服了平均场近似预测主体相热力学性质时的偏差,获得的密度分布和吸附等温线与 GCMC 分子模拟结果有着很好的一致性.     

约束条件下的硬球流体

利用密度泛函理论和分子动力学方法 ,对处于两平行硬墙之间的硬球流体的密度分布进行了计算 .通过比较两种方法的结果 ,发现在墙之间距离较大时 ,Rosenfeld密度泛函理论的结果与分子动力学模拟的结果符合很好 ;当两堵墙间的距离很小时 ,这两个结果之间存在明显的不一致 .另外 ,还研究了约束条件下密度分布的结构     

饱和态金属熔体热力学性质的计算

本文应用聚集硬球引力场模型状态方程和饱和液态状态方程分别计算了五种碱金属熔体的饱和气体和饱和液密度。另外，还基于Clapeyron方程应用Rankine蒸气压方程与状态方程计算了金属熔体的气化热．上述计算结果都非常满意。     

CO2气、液、固三相饱和态下pVT的计算

本文基于分子聚集理论和硬球引力场模型应用分子热力学方法导出CS-vdW状态方程,应用上述方程计算了CO2气-液和气-固平衡相的饱和态下pVT性质.取得了很满意的结果.本方法的优点是使用简便,可供工程计算使用.     

受限于对称性破缺狭缝间氢键流体的相平衡研究

利用密度泛函理论并结合改进的基本度量理论研究了受限于对称性破缺狭缝间氢键流体的相平衡. 首先根据氢键流体的吸附-脱附等温线及相应巨势获得不同条件下氢键流体的相图. 进一步讨论了氢键作用、狭缝间距、狭缝与流体分子间相互作用及对称性破缺程度等因素对氢键流体相平衡的影响. 结果表明, 由于狭缝与流体分子及流体分子间的相互作用存在竞争, 使得受限于对称性破缺条件下的氢键流体呈现更为复杂的相态特征.     

Screening of light impurities in simple metals

The Kohn-Sham density functional method is used to calculate self-consistent electron densities around H, He and Li impurities in jellium host corresponding to Li, Al and Mg metals. The differences in the density profiles for interstitial and substitutional impurities are investigated. Residual resistivities, relaxation energies and charge transfer in dilute alloys are evaluated.     

Grafted polymers with annealed excluded volume: A model for surfactant association in brushes

We present an analytical self-consistent-field (SCF) theory for a neutral polymer brush (a layer of long polymer chains end-grafted to a surface) with annealed excluded volume interactions between the monomer units. This model mimics the reversible adsorption of solute molecules or aggregates, such as small globular proteins or surfactant micelles, on the grafted chains. The equilibrium structural properties of the brush (the brush thickness, the monomer density profile, the distribution of the end segments of the grafted chains) as well as the overall adsorbed amount and the adsorbate density profile are analyzed as a function of the grafting density, the excluded volume parameters and the chemical potential (the concentration) of the adsorbate in the solution. We demonstrate that, when the grafting density is varied, the overall adsorbed amount always exhibits a maximum, whereas the root-mean-square brush thickness either increases monotonically or passes through a (local) minimum. At high grafting densities the chains are loaded by adsorbed aggregates preferentially in the distal region of the brush, whereas in the region proximal to the grafting surface depletion of aggregates occurs and the polymer brush retains an unperturbed structure. Depending on the relative strength of the excluded volume interactions between unloaded and loaded monomers both the degree of loading of the chains and the polymer density profile are either continuous or they exhibit a discontinuity as a function of the distance from the grafting surface. In the latter case intrinsic phase separation occurs in the brush: the dense phase consists of unloaded and weakly extended chains and occupies the region proximal to the surface, whereas a more dilute phase consisting of highly loaded and strongly extended chains forms the periphery of the brush. Received 26 November 1998 and Received in final form 2 April 1999     

An integrated simulation and statistical technique for?investigating the effect of interpenetration polymer brushes in a good solvent

This study presents a novel approach for analyzing the interaction between two parallel surfaces grafted with polymer brushes in a good solvent. In the proposed approach, MD simulations are performed to establish the mean brush height and the standard deviation of the brush height distribution for a given value of the surface separation. The corresponding probability density function (PDF) of the brush height is then determined both with and without the assumption of a brush interpenetration effect, respectively, and a statistical technique is applied to compute the corresponding interaction free energy per unit area of the grafted substrates. Finally, the Derjaguin approximation is employed to determine the corresponding value of the interaction force between the two surfaces. The results obtained for the interaction free energy and interaction force are compared with those derived using the Alexander and de Gennes (AdG) model and the Milner, Witten and Cates (MWC) model, respectively. The value of the normalized interaction free energy computed using the present method is higher than that obtained from the AdG and MWC models at larger surface separations when the brush interpenetration effect is ignored. However, the results obtained by the current method for the interaction force are found to be in better agreement with the experimental data than those obtained using the AdG or MWC models. The enhanced performance of the proposed method is attributed primarily to the use of an adaptive non-Gaussian PDF of the brush height to model the effects of brush interpenetration and fluctuations in the brush conformation at different distances from the grafting plane.     

Quantum corrections to the thermodynamic properties of a two-dimensional fluid with hard-core potential

A simple theory, based on the physical interpretation of the reciprocal of activity, is developed to evaluate the thermodynamic properties of a two-dimensional fluid in the semi-classical limit. The theory is applied to calculate the quantum corrections to the equation of state and excess free energy of two-dimensional fluids, whose molecules interactvia hard-disc and square-well potential. It is found that the quantum effect increases with the increase of density and decrease of temperature.     

H2在Li掺杂Al6Si+上吸附的理论研究

本文利用密度泛函理论的B3LYP/6-31G(d, p)和组态相互作用的QCISD/6-31G(d, p)研究了Al6Si+和Al6SiLi+团簇的几何和电子结构及其对H2分子的吸附,两种不同方法计算的H2分子在团簇上的吸附能非常一致。H2分子在Al6Si+团簇上的吸附能仅为-0.018 eV,Al6Si+团簇中掺杂Li原子可以明显增强其对H2分子的吸附。Al6SiLi+团簇吸附一个H2分子的吸附能可以达到-0.157 eV,吸附五个H2分子的平均吸附能为-0.088 eV。态密度和自然键轨道分析表明,电荷从Li原子向Si原子转移,H2分子在带正电的Li离子产生的电场中发生极化,从而在静电相互作用下吸附在Li原子周围。     

Li修饰的C$lt;sub$gt;6$lt;/sub$gt;分子对H$lt;sub$gt;2$lt;/sub$gt;O的吸附研究

采用密度泛函理论中的广义梯度近似研究C₆Li吸附H₂O分子并将之进行分解的催化过程. 几何优化发现：Li原子最稳定的吸附位置是位于C 原子顶位上方. 研究表明,第一个H₂O 分子吸附在C₆Li上需要克服1.77 eV的能量势垒,然后分解为H和OH且与Li原子成键. 当吸附第二个H₂O分子时,第二个H₂O分子需要克服1.2 eV的能量势垒分解为H和OH,其中H与Li原子上的H原子结合成H₂,OH则替代Li 原子上的H结合在Li原子上. 因此C₆Li 可以作为催化剂将H₂O分子进行分解得到H₂. 分析可知：C₆Li主要是通过Li原子与H₂O之间形成的偶极矩作用来吸附H₂O 分子,与C₆₀Li₁₂ 的储氢机制类似. 研究结果可为储氢材料的制备提供一个新的思路. 关键词： 6')" href="#">C₆ Li 2O')" href="#">H₂O 密度泛函理论     

Charged Nanoparticle Transport in Polymer-Grafted Nanochannels

Molecular dynamics simulations were used to investigate the electric field-induced migration of nanoparticles in a nanochannel grafted with a polymer brush. The distribution of nanoparticles, brush monomer density and migration velocity are addressed at different electric field strengths and grafting densities. The increase of the grafting density leads to a decrease of the effective radius of the nanochannel. At high grafting density, the distribution of nanoparticles is shifted significantly towards the center of the channel. Enhancing the electric field leads to a very slight change of brush monomer density. The migration velocity increases with the electric field rapidly at weak electric fields, while a slow increase is observed at strong electric fields. Additionally, it is found that the migration velocity of nanoparticles exhibits a nonlinear dependence on the grafting density.     

Li原子修饰笼型Si6团簇的结构和储氢性能

利用杂化密度泛函B3LYP方法, 在6-311+G(d, p)基组水平上对Si6和Li修饰的Si6团簇的几何结构和电子性质及储氢性能进行模拟计算和理论研究. 结果表明, Si6团簇最低能量构型为笼型结构, 纯Si6团簇不能有效吸附氢分子. Li原子的引入显著改善了Si6团簇的储氢能力. 以两个Li原子端位修饰Si6团簇为载体, 其氢分子的平均吸附能为1.692~2.755 kcal/mol, 每个Li原子周围可以有效吸附五个氢分子, 储氢密度可达9.952wt%. 合适的吸附能和较高储氢密度表明Li修饰Si6团簇有望成为理想的储氢材料.