Prediction of a Neutral Noble Gas Compound in the Triplet State

Discovery of the HArF molecule associated with H?Ar covalent bonding [Nature, 2000 , 406, 874–876] has revolutionized the field of noble gas chemistry. In general, this class of noble gas compound involving conventional chemical bonds exists as closed‐shell species in a singlet electronic state. For the first time, in a bid to predict neutral noble gas chemical compounds in their triplet electronic state, we have carried out a systematic investigation of xenon inserted FN and FP species by using quantum chemical calculations with density functional theory and various post‐Hartree–Fock‐based correlated methods, including the multireference configuration interaction technique. The FXeP and FXeN species are predicted to be stable by all the computational methods employed in the present work, such as density functional theory (DFT), second‐order Møller–Plesset perturbation theory (MP2), coupled‐cluster theory (CCSD(T)), and multireference configuration interaction (MRCI). For the purpose of comparison we have also included the Kr‐inserted compounds of FN and FP species. Geometrical parameters, dissociation energies, transition‐state barrier heights, atomic charge distributions, vibrational frequency data, and atoms‐in‐molecules properties clearly indicate that it is possible to experimentally realize the most stable state of FXeP and FXeN molecules, which is triplet in nature, through the matrix isolation technique under cryogenic conditions.     

气体分子在二维石墨烯纳米孔中的选择性渗透特性

二维石墨烯纳米孔中气体分子的选择性渗透对多孔石墨烯分离膜非常重要。本文采用分子动力学方法研究了气体分子在氮氢修饰石墨烯纳米孔中的渗透特性,从分子的大小和结构、纳米孔的构型以及分子与石墨烯之间的作用强度等角度阐明了分子出现选择性渗透的原因。结果表明,不同分子的渗透率不同,即H₂O＞H₂S＞CO₂＞N₂＞CH₄。渗透率跟分子的质量和直径以及分子在石墨烯表面上的吸附密度有关;根据气体分子动理学理论,渗透率跟分子质量成反比关系;而分子在石墨烯表面上的高吸附密度对渗透起促进作用。对于H₂O和CH₄分子,分子直径起主导作用;H₂O分子直径最小,其渗透率最大;同理,CH₄分子的渗透率最小。对于H₂S和CO₂分子,H₂S分子的直径较大,但其与石墨烯之间的作用强度较大(吸附密度较高),导致渗透率较高;对于CO₂和N₂分子,CO₂分子的直径较小,并且与石墨烯之间的作用强度较大,渗透率较高。同时发现,分子在纳米孔中的渗透使得其在石墨烯表面的密度分布极不均匀。纳米孔左右两侧的功能化氮原子使CH₄分子容易从孔两侧区域穿过,而其它分子由于直径较小在纳米孔中心区域穿过的概率最大。分子与石墨烯之间的作用越强,导致分子在石墨烯表面区域内停留的时间越长,最终使其在渗透纳米孔的过程中所经历的时间越长。本文所采用的氮氢修饰石墨烯纳米孔中,分子渗透速率达到~10^-3 mol·s^-1·m^-2·Pa^-1,并且其它分子相对于CH₄分子的选择性也很高,说明基于该类型纳米孔的多孔石墨烯分离膜在天然气处理等工业气体分离领域具有很好的应用前景。     

气相中La催化乙烯脱氢及C-C键耦合的理论研究

采用密度泛函理论中的B3LYP方法研究了气相中过渡金属La在二、四重态势能面上催化C2H4的反应机理。全参数优化了二、四重态势能面上各个驻点的几何构型,同时对过渡态进行了频率分析,使用内禀反应坐标（IRC）方法验证了过渡态的准确性,通过AIM理论和NBO分析方法对主要的驻点进行了键分析,并对2IM1、2IM3进行了态密度分析。结果表明：La与C2H4的反应存在两种可能的路径,反应在二重态势能面上进行且均为放热反应。键分析表明初始复合物中La与C2H4分子之间为共价作用。     

How Accessible Is Atomic Charge Information from Infrared Intensities? A QTAIM/CCFDF Interpretation

Infrared fundamental intensities calculated by the quantum theory of atoms in molecules/charge-charge flux-dipole flux (QTAIM/CCFDF) method have been partitioned into charge, charge flux, and dipole flux contributions as well as their charge-charge flux, charge-dipole flux, and charge flux-dipole flux interaction contributions. The interaction contributions can be positive or negative and do not depend on molecular orientations in coordinate systems or normal coordinate phase definitions, as do CCFDF dipole moment derivative contributions. If interactions are positive, their corresponding dipole moment derivative contributions have the same polarity reinforcing the total intensity estimates whereas negative contributions indicate opposite polarities and lower CCFDF intensities. Intensity partitioning is carried out for the normal coordinates of acetylene, ethylene, ethane, all the chlorofluoromethanes, the X(2)CY (X = F, Cl; Y = O, S) molecules, the difluoro- and dichloroethylenes and BF(3). QTAIM/CCFDF calculated intensities with optimized quantum levels agree within 11.3 km mol(-1) of the experimental values. The CH stretching and in-plane bending vibrations are characterized by significant charge flux, dipole flux, and charge flux-dipole flux interaction contributions with the negative interaction tending to cancel the individual contributions resulting in vary small intensity values. CF stretching and bending vibrations have large charge, charge-charge flux, and charge-dipole flux contributions for which the two interaction contributions tend to cancel one another. The experimental CF stretching intensities can be estimated to within 31.7 km mol(-1) or 16.3% by a sum of these three contributions. However, the charge contribution alone is not successful at quantitatively estimating these CF intensities. Although the CCl stretching vibrations have significant charge-charge flux and charge-dipole flux contributions, like those of the CF stretches, both of these interaction contributions have opposite signs for these two types of vibrations.     

Calculation of mean-square vibrational amplitudes and shrinkage for linear triatomic molecules of AB2 type

Formulae for the calculation of shrinkage and mean-square amplitudes for linear molecules of AB₂ type have been derived without the use of small harmonic vibration theory. The probability density of the internuclear distance distribution being calculated with allowance for the rotation—vibration interaction. The formulae obtained agree, within experimental error, with electron diffraction data for molecules characterized by large displacements of the nuclei from their equilibrium positions. These data cannot be described by the relations usually employed in gas electron-diffraction investigations.     

Phase behavior of condensate gas and CO2 / CH4 re-injection performance on its retrograde condensation

Wenchang A Depression in Pearl River Mouth Basin is the largest hydrocarbon generating depression in the west of the area. After more than 30 years of exploitation, a large amount of gas condensate has been produced near the wellbore, which will cause gas condensate damage to the reservoir. It is planned to reinject the self-produced gas from Well WC9-2-X and the gas transported from the WC14-3 gas field to relieve the condensate damage in the near-wellbore area by means of retrograde condensation. In this article, the phase state change process of condensate gas in Well WC9-2-X with temperature and pressure was firstly investigated, and then the retrograde condensation effect of two types of gas on condensate was investigated. The research shows that when the reservoir temperature is 158.80 °C, the dew point pressure of condensate gas is 20.71 MPa, and the maximum amount of condensate is 1.28% (P = 9.01 MPa). Although Wenchang 9–2 is a low condensate reservoir, in the process of depressurization and production over the years, gas condensate has gradually accumulated, resulting in a large amount of gas condensate near the wellbore. With the increase of the gas re-injection amount, the two types of gas have a significant effect on the retrograde condensation of the gas condensate. From the variation trend of the gas and oil density released by the retrograde condensation, it can be seen that the re-injection gas preferentially dissolves the light components in the condensate, and then gradually dissolves the heavy components. The self-produced gas (gas No. 1) of Well WC9-2-X is dominated by CH₄ (78.33 mol%), and the CO₂ / CH₄ contents in the input waste gas (gas No. 2) of the WC14-3 gas field are 42.50 mol% / 41.60 mol%, respectively. The retrograde condensation effect of gas No. 2 is better than gas No. 1, mainly because the content of CO₂ in gas No. 2 is high, and it is easier to achieve the effect of miscible dissolution of condensate when mixed with condensate.It is recommended that gas No.2 should be preferentially used in WC9-2-X well for reinjection of retrograde condensation to relieve condensate damage. This article provides theoretical support for gas re-injection to relieve condensate damage in Wenchang 9–2 gas field, and has important significance for long-term exploitation of condensate gas reservoir.     

Molecular dynamics simulation of the equilibrium liquid–vapor interphase with solidification

The equilibrium structure of the finite, interphase interfacial region that exists between a liquid film and a bulk vapor is resolved by molecular dynamics simulation. Argon systems are considered for a temperature range that extends below the melting point. Physically consistent procedures are developed to define the boundaries between the interphase and the liquid and vapor phases. The procedures involve counting of neighboring molecules and comparing the results with boundary criteria that permit the boundaries to be precisely established. Two-dimensional radial distribution functions at the liquid and vapor boundaries and within the interphase region demonstrate the physical consistency of the boundary criteria and the state of transition within the region. The method developed for interphase boundary definitions can be extended to nonequilibrium systems. Spatial profiles of macroscopic properties across the interphase region are presented. A number of interfacial thermodynamic properties and profile curve-fit parameters are tabulated, including evaporation/condensation coefficients determined from molecular flux statistics. The evaporation/condensation coefficients away from the melting point compare more favorably with transition state theory than those of previous simulations. Near the melting point, transition theory approximations are less valid and the present results differ from the theory. The effects of film substrate wetting on evaporation/condensation coefficients are also presented.     

Adsorption-induced deformation of mesoporous solids: macroscopic approach and density functional theory

We present a theoretical study of the deformation of mesoporous solids during adsorption. The proposed thermodynamic model allows one to link the mechanical stress and strain to the solvation pressure exerted by the adsorbed molecules on the pore wall. Two approaches are employed for calculation of solvation pressure as a function of adsorbate pressure: the macroscopic Derjaguin-Broekhoff-de Boer theory of capillary condensation, and the microscopic density functional theory. We revealed that the macroscopic and microscopic theories are in quantitative agreement for the pores >8 nm diameter within the whole range of adsorbate pressures. For smaller pores, the macroscopic theory gradually deteriorates, and the density functional theory extends the thermodynamic model of adsorption-induced deformation to the nanometer scales.     

Thermodynamic driving force for diffusion: comparison between theory and simulation

In previous work, lattice density functional theory equations have been recast into differential form to determine a property whose gradient is universally proportional to the diffusive flux. For color counter diffusion, this property appears as the impingement rate onto vacancies and molecules of a species whose density gradient can be influenced by diffusion. Therefore, the impingement rate of a diffusing molecule depends on the mobility of its surroundings. In order to determine the validity of this finding, molecular dynamics simulations of color counter diffusion were performed in which the mobility of the solvent was varied to determine if the flux of the diffusing species responded to the change when all other factors, such as density gradient, available volume, and temperature are held constant.     

A solvation‐free‐energy functional: A reference‐modified density functional formulation

The three‐dimensional reference interaction site model (3D‐RISM) theory, which is one of the most applicable integral equation theories for molecular liquids, overestimates the absolute values of solvation‐free‐energy (SFE) for large solute molecules in water. To improve the free‐energy density functional for the SFE of solute molecules, we propose a reference‐modified density functional theory (RMDFT) that is a general theoretical approach to construct the free‐energy density functional systematically. In the RMDFT formulation, hard‐sphere (HS) fluids are introduced as the reference system instead of an ideal polyatomic molecular gas, which has been regarded as the appropriate reference system of the interaction‐site‐model density functional theory for polyatomic molecular fluids. We show that using RMDFT with a reference HS system can significantly improve the absolute values of the SFE for a set of neutral amino acid side‐chain analogues as well as for 504 small organic molecules. © 2015 Wiley Periodicals, Inc.     

THE GAS TRANSPORT BEHAVIOR IN AROMATIC POLYESTER MEMBRANES

Six aromatic polyesters were prepared for gas separation membranes, and their per-meation properties for hydrogen, oxygen, nitrogen, carbon dioxide, and methane weremeasured at 30℃ and 1 atmosphere by low pressure manometric method. The cor-relation between the gas transport behavior and molecular structure of aromatic polyestermembrane is discussed. These data are interpreted qualitatively in terms of the calculatedpacking density, gas-polymer interaction, concentration of aryl bromine on backbone, andeffect of silane group on main chain of polymer.     

The quantum theory of atoms in positronic molecules: The subsystem variational procedure

This contribution deals with the subsystem variational procedure within the context of the quantum theory of atoms in positronic molecules (QTAIPM). Before introducing the subsystem energy functional termed as joint subsystem energy functional, a novel notation and the combination strategy are disclosed in detail by restating the positronic subsystem hypervirial theorem. They are employed in proposing the proper subsystem energy functional, the validity of which is checked by various criteria. The zero flux surfaces of the joint density distribution are used to define the topological atoms in the positronic molecules, and they are incorporated into the subsystem variational procedure as proper real space boundary conditions. The variational procedure finally yields the flux of the joint current property density that also appears in the positronic subsystem hypervirial theorem. At every stage, the corresponding equations for the purely electronic systems within the context of the quantum theory of atoms in molecules (QTAIM) are presented to clearly reveal the analogy between these two formalisms and to emphasize the importance of combining the property density distributions in the QTAIPM. The presented material demonstrates the internal consistency of the whole framework and discloses the fact that the QTAIM must be regarded as a variant of the QTAIPM. Furthermore, this formalism promises an extended QTAIM, which is hoped to resolve the issue of molecular structure beyond the clamp nuclei approximation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Effect of attractions on the structure of polymer solutions confined between surfaces: a density functional approach

A density functional theory is presented to study the effect of attractions on the structure of polymer solutions confined between surfaces. The polymer molecules have been modeled as a pearl necklace of freely jointed hard spheres and the solvent as hard spheres, both having Yukawa-type attractions and the mixture being confined between attractive Yukawa-type surfaces. The present theory treats the ideal gas free energy functional exactly and uses weighted density approximation for the hard chain and hard sphere contributions to the excess free energy functional. The attractive interactions are calculated using the direct correlation function obtained from the polymer reference interaction site model theory along with the mean spherical approximation closure. The theoretical predictions on the density profiles of the polymer and the solvent molecules are found to agree quite well with the Monte Carlo simulation results for varying densities, chain lengths, wall separations, and different sets of interaction potentials.     

A molecular model of water based on the lattice gas model

A lattice gas model is used to describe the vapor-liquid state of water molecules. The orientationally directed interaction of the water molecules via their tetrahedral structure and dipole-dipole interaction are considered in the theory, along with the Lennard-Jones contributions to the potential of molecular interaction, which stabilize the system with dipole interaction. We studied how the radius of the molecular interaction potential affects the equilibrium characteristics of the system (the phase separation curves of the vapor-liquid system, and the relationship between the fluid density and the chemical potential value).     

Investigating the nature of intermolecular and intramolecular bonds in noble gas containing molecules

This article presents a theoretical study on a number of selected noble gas containing systems of the general formula FNgR and NgR (Ng = He, Ne, Ar, Kr, Xe and R = CH₃, CN, CCH, BO, BNH, H, BeO, and AuF). The principal structures, bond energies, spectroscopic, and electronic properties of 28 noble gas containing molecules were investigated using density functional theory at the BMK level. Quantum theory of atoms in molecules, natural bond orbital, and several other analysis methods have been used to provide more insight into the nature of noble gas bonds. Although both F? Ng and Ng? R bonds in the investigated molecules are assigned to have partially covalent and partially electrostatic nature, the covalent character is dominant in Ng? R bonds. In the second part, the intermolecular interactions between FNgR molecules and hydrogen fluoride are overviewed with emphasis on the hydrogen bonding through the fluorine side of noble gas molecule with hydrogen of HF. The calculated interaction energies were found to decrease in magnitude going down the noble gas series. For all noble gases, the strongest hydrogen bond has been observed in the case R=CH₃. On the contrary, using R=CN in the FNgR moiety weakens the interaction strength. © 2014 Wiley Periodicals, Inc.     

Density functional description of adsorption in slitlike pores modified with chain molecules: a simple model for pillaredlike materials

We propose a density functional theory to describe adsorption of Lennard-Jones fluid in slitlike pores modified by chain molecules. Specifically, the chains are bonded by their ends to the opposite pore walls, so they can form pillaredlike structure. Two models are studied. In the first model, the nonterminating segments of chains can change their configuration inside the pore upon adsorption of spherical species. In the second model, the chains configuration remains fixed, so that the system is similar to a nonuniform quenched-annealed mixture. We study capillary condensation of fluid species inside such modified pores and compare the results obtained for two models.     

Structural properties and the effect of 2,6‐diaminoanthraquinone on G‐tetrad,non‐G‐tetrads,and mixed tetrads—A density functional theory study

Telomerase inhibitor causes the attrition of telomere length and consequently leading to senescence which require a lag period for cancer cells to stop proliferating. Telomeric sequences form quadruplex structures stabilized by tetrads. The structural and electronic properties related with interaction of 2,6‐diaminoanthraquinone and tetrads are the key step to elucidate the anticancer activity. The present study has been focused on the stability of the isolated tetrads and the effect of interaction of 2,6‐diaminoanthraquinone with G‐tetrad, non‐G‐tetrads, and mixed tetrads using density functional theory method in both gas and aqueous phases. The solvent interaction with the molecular systems has increased the stability of the isolated tetrads and complexes. The sharing of electron density between the interacting molecules is shown through electron density difference maps. The atoms in molecules theory and natural bond orbital analysis have been performed to study the nature of hydrogen bonds in the inhibitor interacting complexes. The linear correlation is shown between electron density [ρ(r)], and its Laplacian [(²ρ(r)] at the bond critical points. The strong binding nature of 2,6‐diaminoanthraquinone with studied tetrads reveals that this inhibitor is suitable to stabilize the above tetrads and inhibit the telomerase activity. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Adsorption Study of Methane on Activated Meso-carbon Microbeads by Density Functional Theory

A combined method of density functional theory (DFT) and statistics integral equation (SIE) for the determination of the pore size distribution (PSD) is developed based on the experimental adsorption data of nitrogen on activated mesocarbon microbead (AMCMB) at 77K. The pores of AMCMB are described as slit-shaped with PSD.Based on the PSD, methane adsorption and phase behavior are studied by the DFT method. Both nitrogen and methane molecules are modeled as Lennard-Jones spherical molecules, and the well-known Steele‘s 10-4-3 potential is used to represent the interaction between the fluid molecule and the solid wall. In order to test the combined method and the PSD model, the Intelligent Gravimetric Analyzer (IGA-003) was used to measure the adsorption of methane on the AMCMB. The DFT results are in good agreement with the experimental data. Based on these facts,we predict the adsorption amount of methane, which can reach 32.3ω at 299K and 4 MPa. The results indicate that the AMCMBs are a good candidate for adsorptive storage of methane and natural gas. In addition, the capillary condensation and hysteresis phenomenon of methane are also observed at 74.05K.     

A linear scaling study of solvent-solute interaction energy of drug molecules in aqua solution

Solvent-solute interaction energies for three well-known drug molecules in water solution are computed at the Hartree-Fock and B3LYP density functional theory levels using a linear scaling technique, which allows one to explicitly include in the model water molecules up to 14 A away from the solute molecule. The dependence of calculated interaction energies on the amount of included solvent has been examined. It is found that it is necessary to account for water molecules within an 8 A radius around the drug molecule to reach the saturated solvent interaction level. Effects of electron correlation and basis set on solvent-solute interaction energies are discussed.