氢气在炭狭缝微孔内吸附的预测

通过边界的平均场近似,推导二平板狭缝孔格子理论Ono-Kondo吸附等温方程。利用格子模型特性和微观物理学理论,计算氢分子在石墨平面的最大吸附容量。比较由氢分子在石墨平面二典型聚集状态标定的Ono-Kondo方程,并用预测精度较高的方程计算了与文献相同条件下的吸附等温线。在比较了计算结果、试验结果和GCMC分子模拟结果后,对Ono-Kondo吸附等温方程的特点、理论基础作了分析,指出了方程的适用范围。     

BC3复合纳米管的储氢性能研究

采用巨正则蒙特卡罗方法(GCMC)研究了BC3复合纳米管的物理吸附储氢性能,获得了该纳米管在不同温度和压强下的吸附等温线,及其在不同条件下的物理储氢吸附量,并和相应的碳纳米管进行了对比研究.结果表明,BC3纳米管在所有条件下的储氢性能均优于相应的碳纳米管,因而它是一种比碳纳米管更强的氢存储介质,并从纳米管和H2分子以及H2分子和H2分子之间的平均总相互作用能的分布情况等因素出发解释了这两种纳米管有不同储氢行为的原因.     

金刚石延(111)面生长的第一性原理研究

利用密度泛函理论(DFT)对碳原子在镍(111)表面吸附结构进行了计算，得到了吸附能以及态密度 (density of state, DOS)分布，分析了吸附在镍(111)面的碳原子和金刚石(111)面的碳原子的分波态密度(PDOS)，结果表明吸附在镍表面的碳原子具有与金刚石表面碳原子相类似的电子结构特点，即两者都存在孤对的和成键的sp³杂化电子,进而发现吸附在镍表面的碳原子极易与金刚石表面相互作用形成稳定的类金刚石几何结构. 关键词： 密度泛函理论 化学吸附 电子结构 金刚石生长     

微孔无定形碳分子动力学建模及吸附性能研究

使用分于动力学熔融-淬火法(QMD)建立微孔无定形碳原子结构模型,采用巨正则蒙特卡洛法(GCMC)研究CO_2、N_2在模型中的吸附行为。通过与热解聚糠醇制备的微孔无定形碳样品比较,所建模型在径向分布函数、孔径分布函数、吸附等温线等方面有很高的符合度。CO_2、N_2吸附计算表明:所建立的微孔无定形碳模型,对CO_2、N_2混合组分吸附具有很高的选择性,CO_2/N_2吸附比随着温度和压力的增加逐渐降低.     

BC3复合纳米管的储氢性能研究

采用巨正则蒙特卡罗方法（GCMC）研究了BC3复合纳米管的物理吸附储氢性能,获得了该纳米管在不同温度和压强下的吸附等温线,及其在不同条件下的物理储氢吸附量,并和相应的碳纳米管进行了对比研究。结果表明,BC3纳米管在所有条件下的储氢性能均优于相应的碳纳米管,因而它是一种比碳纳米管更强的氢存储介质,并从纳米管和H2分子以及H2分子和H2分子之间的平均总相互作用能的分布情况等因素出发解释了这两种纳米管有不同储氢行为的原因。     

基于密度泛函理论的CO2吸附微观机理比较研究

为探究吸附法捕获CO₂过程中的微观机理和吸附剂材料间的作用关系,基于密度泛函理论方法,综合比较了典型吸附剂包括煤基官能团、Fe、限域离子液体、Na₂CO₃、SrTiO₃与CO₂的吸附过程和差异性.根据不同计算策略,着重分析比较了吸附能、结构优化参数、吸附构型以及原子分布等参数.结果表明,化学吸附中CO₂分子与吸附面呈平行关系时通常吸附能最大;在一种材料的同类型官能团中,吸附能大小与氧原子的数量呈正相关关系;吸附过程中C-O键的伸长活化会生成一种重要的中间产物CO₂^-.提出在探寻CO₂吸附材料时可以在含氧原子较多的官能团、活性金属表面等方面进一步探究.最后对基于密度泛函理论的CO₂的吸附机理的进一步研究方向进行了展望.     

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     

单个钛原子储氢能力和储氢机制的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了单个过渡金属钛原子吸附氢分子的物理机制. 研究表明,单个钛原子最多能吸附8对氢分子,吸附结构为对称的两个类金字塔型结构, 其平均吸附能为- 0.28 eV.通过计算轨道能级和差分电荷密度分布,分析决定吸附结构、 吸附能大小以及吸附氢分子数目的内在物理机制.研究表明,钛原子的4s电子转移到3d轨道上, 从而产生较强的极化电场,导致氢分子极化,钛原子通过静电极化作用吸附氢分子. 本文的研究将对设计高密度储氢材料有一定的指导作用.     

接枝聚合物对小分子的选择性吸附研究

文章应用密度泛函理论研究接枝于壁面的方阱链对二元小分子混合物的选择性吸附特性. 系统的Helmholtz剩余自由能泛函被表示为硬球排斥和方阱吸引两部分贡献之和,分别由硬球链流体状态方程和变阱宽方阱链流体状态方程的简单加权密度近似来进行计算. 用此理论方法,分别考察了接枝聚合物的结构性质,以及不同温度下接枝分子层对二元方阱流体的选择性吸附性能. 结果表明:分子刷厚度随接枝密度线性增长而随温度非线性增加,并且在高温下趋于饱和;在较低温度下,接枝聚合物刷能表现出很好的选择性吸附能力,当聚合物刷被加热到高于饱和温度时,该能力将大幅度地减弱. 关键词： 密度泛函理论 接枝聚合物 选择性吸附 方阱链     

氮掺杂双层石墨烯吸附钠的第一性原理研究

采用密度泛函理论(DFT)的第一性原理方法,对Na在本征双层石墨烯(PBLG)和不同掺杂浓度的N掺杂石墨烯(NBLG)表面的吸附性质进行了研究.确定了不同N掺杂浓度时NBLG的最稳定N分布结构,计算了Na在PBLG和不同掺杂浓度的NBLG表面的吸附能.计算结果表明,N原子掺杂倾向于取代对位或次临近位置的C原子,并与下层C原子相对;随着N掺杂浓度的增加,吸附高度逐渐增加,且与掺杂N原子分布相匹配; Na在PBLG表面吸附使平均层间距增加,而在NBLG表面吸附使之减小; Na与C_(27)N_9表面的结合最稳定.     

A new study of associating inhomogeneous fluids with classical density functional theory

ABSTRACT

A new density functional for the study of associating inhomogeneous fluids based on Wertheim's first-order thermodynamic perturbation theory is presented and compared to the most currently used associating density functionals. This functional is developed using the weighted density approximation in the range of association of hard spheres. We implement this functional within the framework of classical density functional theory together with modified fundamental measure theory to account for volume exclusion of hard spheres. This approach is tested against molecular simulations from literature of pure associating hard spheres and mixtures of non-associationg and associating hard spheres with different number of bonding sites close to a hard uniform wall. Furthermore, we compare and review our results with the performance of associating functionals from literature, one based on fundamental measure theory and the inhomogeneous version of Wertheim's perturbation theory. Results obtained with classical DFT and the three functionals show excellent agreement with molecular simulations in systems with one hard wall. For the cases of small pores where only one or two layers of fluid are allowed discrepancies between results with classical DFT and molecular simulations were found.     

Experimental and computational study of visible light-induced photocatalytic ability of nitrogen ions-implanted TiO2 nanotubes

Nitrogen-doped TiO2 nanotubes(TNTs)were prepared by ion implantation and anodic oxidation.The prepared samples were applied in photocatalytic(PC)oxidation of methyl blue,rhodamine B,and bisphenol A under light irradiation.To explore the influence of doped ions on the band and electronic structure of TiO2,computer simulations were performed using the VASP code implementing spin-polarized density functional theory(DFT).Both substitutional and interstitial nitrogen atoms were considered.The experimental and computational results propose that the electronic structure of TiO2 was modified because of the emergence of impurity states in the band gap by introducing nitrogen into the lattice,leading to the absorption of visible light.The synergy effects of tubular structures and doped nitrogen ions were responsible for highly efficient and stable PC activities induced by visible and ultraviolet(UV)light.     

Density functional theory study on ion adsorption and electroosmotic flow in a membrane with charged cylindrical pores†

ABSTRACT

Ion adsorption and electroosmotic flow induced by an external electric field have a variety of practical applications, especially for membrane technology. In this work, a partially perturbative density functional theory (DFT) based on the modified fundamental measure theory was applied to investigate the ion density distributions and partitions in a charged cylindrical pore. Different types of electrolyte solutions, including both charge symmetric and asymmetric, were examined using the proposed theory with various pore diameters, bulk densities, ion valencies and surface charge densities. The ion concentration profiles calculated with the theory exhibit good agreements with the results of the Monte Carlo simulations, while the results of the Poisson–Boltzmann equation deviate greatly especially for the high valence electrolytes in narrow cylindrical pores. Some interesting phenomena discovered in both experiments and simulations, such as the reverse distribution of the ions and charge inversion, can be well reproduced with the DFT. Based on the ion concentration distributions obtained from the DFT, the transient velocity profiles of the electroosmotic flow in the charged cylindrical nanopores were calculated with the Navier–Stokes (NS) equation. The characteristics of the electroosmotic flow were discussed under the different bulk electrolyte concentrations and thickness of the electric double layer inside the nanopore. The enhancement of the velocity near the pore wall, which cannot be described by the traditional theory, was well characterised by the DFT combined with the NS equation.     

Two-dimensional roughening of adsorbate islands in thermodynamic equilibrium

Equilibrium fluctuations of islands of adsorbed O atoms on Ru(0001) were investigated by scanning tunneling microscopy (STM), density functional theory calculations (DFT) and Monte Carlo (MC) simulations. Very ramified (2 x 2)-O islands were observed by high-speed STM that point to complex interactions between the O atoms. The DFT calculations show that, in addition to pairwise attractive interactions between third-nearest neighbors, a repulsive three-body interaction exists between these. MC simulations that include three-body interactions reproduce the observed ordering behavior.     

One-body potential theory of molecules and solids modified semiempirically for electron correlation

The study of Cordero, March and Alonso (CMA) for four spherical atoms, Be, Ne, Mg and Ar, semiempirically fine-tunes the Hartree-Fock (HF) ground-state electron density by inserting the experimentally determined ionization potentials. The present Letter, first of all, relates this approach to the very recent work of Bartlett ‘towards an exact correlated orbital theory for electrons’. Both methods relax the requirement of standard DFT that a one-body potential shall generate the exact ground-state density, though both work with high quality approximations. Unlike DFT, the CMA theory uses a modified HF non-local potential. It is finally stressed that this potential generates also an idempotent Dirac density matrix. The CMA approach is thereby demonstrated to relate, albeit approximately, to the DFT exchange-correlation potential.     

Large-scale atomistic simulations of nanostructured materials based on divide-and-conquer density functional theory

A linear-scaling algorithm based on a divide-and-conquer (DC) scheme is designed to perform large-scale molecular-dynamics simulations, in which interatomic forces are computed quantum mechanically in the framework of the density functional theory (DFT). This scheme is applied to the thermite reaction at an Al/Fe₂O₃ interface. It is found that mass diffusion and reaction rate at the interface are enhanced by a concerted metal-oxygen flip mechanism. Preliminary simulations are carried out for an aluminum particle in water based on the conventional DFT, as a target system for large-scale DC-DFT simulations. A pair of Lewis acid and base sites on the aluminum surface preferentially catalyzes hydrogen production in a low activation-barrier mechanism found in the simulations.     

Wave packet molecular dynamics–density functional theory method for non‐ideal plasma and warm dense matter simulations

A new wave packet molecular dynamics–density functional theory (WPMD‐DFT) method is proposed for atomistic simulations of non‐ideal plasma and warm dense matter. The method is based on the WPMD approach, where the electronic exchange and correlation effects are treated using an additional energy term taken from DFT. This term is calculated by integration over the mesh values of the wave packet density. The local density approximation is implemented so far. WPMD‐DFT is meant as a replacement for the anti‐symmetrized WPMD (AWPMD) method which is more time consuming and lacks electron correlation. In this paper, we compare the results obtained by WPMD‐DFT, WPMD, AWPMD, classical molecular dynamics, and path integral Monte Carlo methods for the internal energy of the hydrogen plasma in the temperature range 10–50 kK and electron number density from 10²⁰ to 10²⁴ cm^?3. We also demonstrate the ability to handle the simultaneous dynamics of electrons and ions by calculating the electron–ion temperature relaxation. The scalability of the WPMD‐DFT method with the number of electrons is shown for implementations in central processing unit and graphical processing unit.     

Hydrogen storage in BC3 composite single-walled nanotube:a combined density functional theory and Monte Carlo investigation

This paper applies a density functional theory(DFT) and grand canonical Monte Carlo simulations(GCMC) to investigate the physisorptions of molecular hydrogen in single-walled BC 3 nanotubes and carbon nanotubes.The DFT calculations may provide useful information about the nature of hydrogen adsorption and physisorption energies in selected adsorption sites of these two nanotubes.Furthermore,the GCMC simulations can reproduce their storage capacity by calculating the weight percentage of the adsorbed molecular hydrogen under different conditions.The present results have shown that with both computational methods,the hydrogen storage capacity of BC 3 nanotubes is superior to that of carbon nanotubes.The reasons causing different behaviour of hydrogen storage in these two nanotubes are explained by using their contour plots of electron density and charge-density difference.     

Adsorption and interfacial phenomena of a Lennard-Jones fluid adsorbed in slit pores: DFT and GCMC simulations

ABSTRACT

Confinement of fluids in porous media leads to the presence of solid–fluid (SF) interfaces that play a key role in many different fields. The experimental characterisation of SF interfacial properties, in particular the surface tension, is challenging or not accessible. In this work, we apply mean-field density functional theory (DFT) to determine the surface tension and also density profile of a Lennard-Jones fluid in slit-shaped pores for realistic amounts of adsorbed molecules. We consider the pore walls to interact with fluid molecules through the well-known 10-4-3 Steele potential. The results are compared with those obtained from Monte Carlo simulations in the Grand Canonical Ensemble (GCMC) using the test-area method. We analyse the effect on the adsorption and interfacial phenomena of volume and energy factors, in particular, the pore diameter and the ratio between SF and fluid–fluid dispersive energy parameters, respectively. Results from DFT and GCMC simulations were found to be comparable, which points to their reliability.