Universality principle and the development of classical density functional theory

The universality principle of the free energy density functional and the ‘test particle' trick by Percus are combined to construct the approximate free energy density functional or its functional derivative. Information about the bulk fluid radial distribution function is integrated into the density functional approximation directly for the first time in the present methodology. The physical foundation of the present methodology also applies to the quantum density functional theory.     

Investigation of vapour--liquid nucleation properties for spherical and chain-like fluids by density functional theory

The excess Helmholtz free energy functional for nonpolar chain-like molecules is formulated in terms of a weighted density approximation （WDA） for short-range interactions and a Weaks Chandler Andersen （WCA） approximation and a Barker Henderson （BH） theory for long-range attraction. Within the framework of density functional theory （DFT）, vapour liquid interracial properties including density profile and surface tension, and vapour-liquid nucleation properties including density profile, work of formation and number of particles are investigated for spherical and chain- like molecules. The obtained vapour liquid surface tension and the number of particles in critical nucleus for Lennard- Jones （L J） fluids are consistent with the simulation results. The influences of supersaturation, temperature and chain length on vapour liquid nucleation properties are discussed.[第一段]     

Lattice density functional theory for confined Ising fluids: comparison between different functional approximations in slit pore

ABSTRACT

In this paper, Lafuente and Cuesta's cluster density functional theory (CDFT) and lattice mean field approximation (LMFA) are formulated and compared within the framework of lattice density functional theory (LDFT). As a comparison, an LDFT based on our previous work on nonrandom correction to LMFA is also developed, where local density approximation is adopted on the correction. The numerical results of density distributions of an Ising fluid confined in a slit pore obtained from Monte Carlo simulation are used to check these functional approximations. Due to rational treatment on the coupling between site-excluding entropic effect and contact-attracting enthalpic effect by CDFT with Bethe-Peierls approximation (named as BPA-CDFT for short), the improvement of BPA-CDFT beyond LMFA is checked as expected. And it is interesting that our LDFT has a comparative accuracy with BPA-CDFT. Apparent differences between the profiles such as solvation force, excess adsorption quantity and interfacial tension from LMFA and non-LMFAs are found in our calculations. We also discuss some possible theoretical extensions of BPA-CDFT.     

On the solvation force of water-like fluid models with square-well attraction and site–site association in slit-like pores: density functional approach

The solvation force of the water-like fluid models with square-well attraction and site–site chemical association confined to slit-like pores has been explored. Theoretical procedure is based on the application of the density functional approach with mean-field approximation for the attractive interparticle interactions. The chemical association effects are treated by using the first-order thermodynamic perturbation theory of Wertheim. Trends of behaviour of the solvation force are put in correspondence with the distribution of molecules in the pores and with the average density of the adsorbate. Moreover, the distribution of non-bonded species on pore width is described. The influence of the width of the square-well and of the gas–solid attraction is discussed. A comparison of theoretical predictions with computer simulations results for water models in slit-like pores is performed.     

Density functional study of the pressure tensor for inhomogeneous Lennard—Jones fluids

Based on classical density functional theory,an expression of the pressure tensor for inhomogeneous fluids is presented.This takes into account greater correlation between particles,especially for systems that are geometrically confined or involve an interface.The density and pressure components of Lennard-Jones fluids confined in hard and softened nano-cavities are calculated.A comparison between the results of this work and IK expression suggests that the agreement depends on temperature.The interfacial tension for hard sphere fluids agrees well with the Monte Carlo result when the bulk density is not too large.The results of the solid-fluid interfacial tension for Lennard-Jones fluids demonstrate that different types of external potentials modulate the interfacial tension in different manners.     

A perturbation density functional theory for hydrogen bonding cyclic molecules

Using the framework of Wertheim's thermodynamic perturbation theory, a new polyatomic density functional theory is developed to account for the intermolecular association of cyclic molecules in interfacial systems. To test the theory, Monte Carlo simulations in the canonical ensemble were performed for the specific case of an associating triatomic ring with one association site next to a hard wall. The theory and simulation results were found to be in good agreement.     

Clathrate hydrates modelled with classical density functional theory coupled with a simple lattice gas and van der Waals-Platteeuw theory

Predicting clathrate hydrate phase equilibria is of interest in the area of natural gas exploitation. This proof of concept study presents the application of a simple lattice gas model and classical density functional theory coupled with van der Waals-Platteeuw theory to predict clathrate hydrate phase equilibria for several different hydrate-forming gas species. The dissociation pressure curve is predicted using adsorption isotherms predicted for the gas species in the crystal hydrate lattice. Comparisons are made between predicted phase equilibria (and other properties) and available experimental data.     

Density functional approximations for classical fluids with long-range interactions

Density functional approximations for systems interacting via long-range forces are revisited. The theory is illustrated with examples of one-component plasmas in two and three dimensions.Dedicated to Philippe Choquard, Coulomb fluid expert.     

Time-dependent density functional theory of classical fluids

We establish a rigorous time-dependent density functional theory of classical fluids for a wide class of microscopic dynamics. We obtain a stationary action principle for the density. We further introduce an exact practical scheme, to obtain hydrodynamical effects in density evolution, that is analogous to the Kohn-Sham theory of quantum systems. Finally, we show how the current theory recovers existing phenomenological theories in an adiabatic limit.     

特丁基对苯二酚的光谱及密度泛函研究

特丁基对苯二酚是重要的食品抗氧化剂.理论上,基于密度泛函理论,采用B3LYP泛函及6-311G(d,p)基组在气相环境下优化分子的结构并进行频率计算.在此基础上,基于含时密度泛函理论,选用SMD(solvation model based on density)溶剂模型,利用B3LYP泛函并结合def2-TZVP基组计...     

Statistical fluid theory for associating fluids containing alternating heteronuclear chain molecules

Statistical associating fluid theory of homonuclear dimerized chain fluids and homonuclear monomer-dimer mixture chain fluids are extended to fluids containing alternating heteronuclear chain molecules separately. The proposed models account for the appropriate site-site correlation functions at contact. The modified equations of state show a good agreement with generalized Flory dimer theory and MD simulation data for small and medium size ratio of hard sphere diameters.     

Imogolite类纳米管直径单分散性密度泛函理论研究

采用密度泛函理论方法研究了三种imogolite类(未取代、NH₂取代和F取代)纳米管的直径单分散性及表面电荷的分布情况, 并从键长方面定性地解释了直径单分散性的原因. 我们给出了IMO, IMO_NH₂和IMO_F的应变能曲线, 结果表明三种纳米管结构的最稳定管径值按照IMO < IMO_NH₂ < IMO_F的顺序递增, 而imogolite类纳米管直径单分散性是由于管径的增大导致内部Si–O, Al–O键与外部Al-OH键键长变化趋势相反造成的, 总之是内部Si–O, Al–O 键和外部Al–OH键相互作用的结果. 此外, 对三种稳定的纳米管结构做了Mulliken布局分析, 并总结了纳米管直径变化对表面电荷的影响. 结果表明正电荷主要积聚在外表面, 而内表面则感应出负电荷, 同时随着纳米管直径的增大表面电荷逐渐增加, 揭示了表面电荷与管径大小的关系. 研究表明, 可以通过改变imogolite内表面不同的官能化取代来控制纳米管直径, 进而调节表面电荷的分布情况, 这在imogolite类材料的分子设计及应用方面有着重要意义.     

Ab-initio density functional theory study of a WO3 NHa-sensing mechanism

WO3 bulk and various surfaces are studied by an ab-initio density functional theory technique. The band structures and electronic density states of WO3 bulk are investigated. The surface energies of different WO3 surfaces are compared and then the （002） surface with minimum energy is computed for its NH3 sensing mechanism which explains the results in the experiments. Three adsorption sites are considered. According to the comparisons of the energy and the charge change between before and after adsorption in the optimal adsorption site Olc, the NH3 sensing mechanism is obtained.     

On the validity of the inverse conjecture in classical density functional theory

It is shown that the basic assumptions of the classical density functional approach are rigorously correct forH-stable systems in the grand canonical ensemble. Moreover, it is established that the set of all single-particle densities is convex. These results are derived by providing necessary and sufficient conditions for the solution of the classical inverse problem for single-particle densities. Analogous results are obtained for the solution of the higher-order correlation inverse problem, and the ramifications of these results for the validity of two-body decomposition of forces are discussed.Research supported in part by the National Science Foundation under grants PHY-8116101 A01 (J.T.C.), PHY-8301493 (L.C.) and PHY-8203669 (J.T.C. and L.C.).     

Hydroxide degradation pathways for guanidimidazolium cation: A density functional theory study

The chemical stability of anion exchange membrane especially in strong alkaline medium under high temperature is one of the crucial challenges for the commercialization of alkaline anion exchange membrane fuel cells. Herein, the degradation mechanism of guanidimidazolium ionic group used in anion exchange membrane was calculated by density functional theory method. The whole transition states of every elemental reaction were systematically searched, and the changes of crucial bonds length were further analyzed for understanding of the reaction mechanism. It was found that the reaction pathway of OH^? attacking guanidinium group of guanidimidazolium was the dominant way for the degradation of guanidimidazolium. Through comparing the energy barriers of guanidimidazolium, imidazolium, and guanidinium, it can be concluded that the electron‐inducing effect had an intimate connection with the alkali stability of ionic groups. The chemical stability of the conjugated structure groups decreased when linking with electron‐drawing groups, while it increased when linking with electron‐donating groups. This work provides theoretical basis for the design of decent alkali‐resistance and high‐performance anion exchange membrane.     

Surface phase transitions of multiple-site associating fluids

Surface phase transitions of Lennard–Jones (LJ) based two- and four-site associating fluids have been studied for various associating strengths using grand-canonical transition matrix Monte Carlo simulations. Our results suggest that, in the case of a smooth surface, represented by a LJ 9-3-type potential, multiple-site associating fluids display a prewetting transition within a certain temperature range. However, the range of the prewetting transition decreases with increasing associating strength and increasing number of sites on the fluid molecules. With the addition of associating sites on the surface, a quasi-2D vapor–liquid transition may appear, which is observed at a higher surface site density for weaker associating fluids. The prewetting transition at lower associating strength is found to shift towards the quasi-2D vapor–liquid transition with increasing surface site density. However, for highly associating fluids, the prewetting transition is still intact, but shifts slightly towards the lower temperature range. Adsorption isotherms, chemical potentials and density profiles are used to characterize surface phase transitions.     

硅团簇自旋电子器件的理论研究

利用过渡金属掺杂的硅基团簇, 构建了一种自旋分子结; 并利用第一性原理方法, 对其电子自旋极化输运性质进行了研究. 计算表明, 通过过渡金属掺杂可以有效地产生自旋极化电流, 磁性金属Fe和非磁性金属Cr和Mn掺杂的体系呈现出较明显的自旋极化透射现象, 但分子结的自旋极化输运能力与团簇孤立状态下的磁矩无一致性.从Sc到Ni的掺杂, 体系的自旋极化透射能力先增大后迅速减小, 在Fe掺杂的Si₁₂团簇中出现最大值. 关键词： 硅团簇 自旋极化输运 密度泛函理论 非平衡格林函数     

A comparative investigation of an AB- and AA-stacked bilayer graphene sheet under an applied electric field: A density functional theory study

An AB- and AA-stacked bilayer graphene sheet(BLG) under an electric field is investigated by ab initio calculation.The interlayer distance between the two layers,band structures,and atomic charges of the system are investigated in the presence of different electric fields normal to the BLG.The AB- stacked BLG is able to tune the bandgap into 0.234 eV with the increase of the external electronic field to 1 V/nm,however,the AA-stacked BLG is not sensitive to the external electric field.In both the cases,the spacing between the BLG slightly change in terms of the electric field.The charges in the AB- stacked BLG are increased with the increase of the electric field,which is considered to be the reason that causes the bandgap opening in the AB- stacked BLG.     

On the relationship between the density functional formalism and the potential distribution theory for nonuniform fluids

It is shown that the variational principle for the grand potential of a nonuniform fluid as a functional of the singlet density yields the potential distribution theory for the equilibrium density. We derive the explicit form that the functional takes for a system of hard rods, and propose an approximate one for hard spheres. Attractive interactions are also considered in mean-field approximation. In all cases the pair direct correlation function of the nonuniform system is obtained and the density gradient expansion of the free energy is investigated.