Computational Studies of Toluene, Methyl Ethyl Ketone, Lubricating and Their Blends: a Combination of Density Functional Theory and Molecular Dynamics

The microstructure and intermolecular interaction of toluene(TOL), methyl ethyl ketone(MEK), lube oil, TOL-MEK solvents, and TOL-MEK-oil solutions were studied by molecular simulation. Some simulation results agree well with the experiment, which suggests that the simulation method we adopted is a powerful tool to obtain microscopic property of the systems. The density functional theory(DFT) calculation results suggest that the interaction group of toluene and MEK is the methyl group of theirs. And the interaction between toluene and MEK is attractive. The contribution of van der Waals interaction to the change of total energy of the TOL-MEK system is major, and the second is electrostatic interaction. Molecular dynamics(MD) simulation analyzes the solubility parameter(SP), mean square displacement(MSD), radius of gyration(RG), and radial distribution function(RDF) of solvents and solutions. The results are that the solubility parameter of the blend solvents decreases with temperature, and increases with the proportion of methyl ethyl ketone in principle, and that of lube oil also trends to decrease with temperature. The MSD results give one reason of why the transmission rate of MEK is greater in membrane separation process of recovery toluene and MEK and the permeation flux increases with MEK:TOL. The RG analysis predicts that the permeability of the oil molecule is likely to rise with temperature during dewaxing solvent recovery process by membrane. The analysis of RDFs shows that the intermolecular interaction of C···C, O···O and C···O makes a major contribution to the total interaction energy.

Structural,Electrical,and Lithium Ion Dynamics of Li2MnO3 from Density Functional Theory

The layered Li2MnO3 is investigated by using the first-principles calculations within the GGA and GGA-t-U scheme, respectively. Within the GGA4-U approach, the calculated intercalation voltage （ranges from 4,5 V to 4.9 V） is found to be in good agreement with experiments. From the analysis of electronic structure, the pure phase Li2MnO3 is insulating, which is indicative of poor electronic-conduction properties. However, further studies of lithium ion diffusion in bulk Li2MnO3 show that unlike the two-dimensional diffusion pathways in rock salt structure layered cathode materials, lithium can diffuse in a three-dimensional pathway in Li2MnO3, with moderate lithium migration energy barrier ranges from 0.57 to 0.63 e V.

Time-dependent density functional theoretical studies on the photo-induced dynamics of an HCI molecule encapsulated in C60 under femtosecond laser pulses

By using first-principles simulations based on time-dependent density functional theory, the chemical reaction of an HCl molecule encapsulated in C60 induced by femtosecond laser pulses is observed. The H atom starts to leave the Cl atom and is reflected by the C60 wall. The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H-Cl bond axis are investigated. The radial oscillation is also found in the two polarization directions of the laser pulse. The relaxation time of the H-Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization. Those results are important for studying the dynamics of the chemical bond at an atomic level.

A novel algorithm for evaluating cement azimuthal density based on perturbation theory in horizontal well

Cement density monitoring plays a vital role in evaluating the quality of cementing projects,which is of great significance to the development of oil and gas.However,the presence of inhomogeneous cement distribution and casing eccentricity in horizontal wells often complicates the accurate evaluation of cement azimuthal density.In this regard,this paper proposes an algorithm to calculate the cement azimuthal density in horizontal wells using a multi-detector gamma-ray detection system.The spatial dynamic response functions are simulated to obtain the influence of cement density on gamma-ray counts by the perturbation theory,and the contribution of cement density in six sectors to the gamma-ray recorded by different detectors is obtained by integrating the spatial dynamic response functions.Combined with the relationship between gamma-ray counts and cement density,a multi-parameter calculation equation system is established,and the regularized Newton iteration method is employed to invert casing eccentricity and cement azimuthal density.This approach ensures the stability of the inversion process while simultaneously achieving an accuracy of 0.05 g/cm^(3) for the cement azimuthal density.This accuracy level is ten times higher compared to density accuracy calculated using calibration equations.Overall,this algorithm enhances the accuracy of cement azimuthal density evaluation,provides valuable technical support for the monitoring of cement azimuthal density in the oil and gas industry.

Insight of Natural Compounds Halimane Diterpenoids against Mycobacterium tuberculosis: Virtual Screening, DFT, Drug-Likeness, and Molecular Dynamics Approach

In the purpose to design novel antituberculosis (anti-TB) drugs agents against Mycobacterium tuberculosis (Mtb), we have built a molecular library around 42 Halimane Diterpenoids isolated from natural sources. Two Mtb enzymes drug targets (Mtb Mycothiol S-transferase and Mtb Homoserine transacetylase) have been adopted. The pharmacological potential was investigated through molecular docking, molecular dynamics simulation, density functional theory (gas phase and water) and ADMET analysis. Our results indicate that (2R,5R,6S)-1,2,3,4,5,6,7,8-octahydro-5-((E)-5-hydroxy-3-methylpent-3-enyl)-1,1,5,6-tetramethylnaphtha-lene-2-ol (compound 20) has displays higher docking score with each of the selected drug targets. In addition, this molecule exhibits a satisfactory drug potential activity and a good chemical reactivity. Its improved kinetic stability in the Mtb Mycothiol S-transferase enzyme reflects its suitability as a novel inhibitor of Mtb growth. This molecule has displayed a good absorption potential. Our results also show that its passive passage of the intestinal permeability barrier is more effective than that of first-line treatments (ethambutol, isoniazid). In the same way, this anti-TB druglikeness has shown to be able to cross the blood brain barrier.

Time-dependent density functional theoretical studies on the photo-induced dynamics of an HCl molecule encapsulated in C_(60) under femtosecond laser pulses

By using first-principles simulations based on time-dependent density functional theory,the chemical reaction of an HCl molecule encapsulated in C60induced by femtosecond laser pulses is observed.The H atom starts to leave the Cl atom and is reflected by the C60wall.The coherent nuclear dynamic behaviors of bond breakage and recombination of the HCl molecule occurring in both polarized parallel and perpendicular to the H–Cl bond axis are investigated.The radial oscillation is also found in the two polarization directions of the laser pulse.The relaxation time of the H–Cl bond lengths in transverse polarization is slow in comparison with that in longitudinal polarization.Those results are important for studying the dynamics of the chemical bond at an atomic level.

Vibrational analysis of L-serine using the density functional theory

In this paper, we present a computational study of L-serine using ab initio molecular dynamics simulation based on density functional theory （DFT） within the ultrasoft pseudopotentials and generalized-gradient approximation. Taking into account the intermolecular interactions, we can indeed simulate the features of the experimental results very well for L-serine zwitterions in its solid state. The vibrational spectrum of L-serine performed by DFT was in excellent agreement with our previous inelastic incoherent neutron scattering spectra measured at 20K for L-serine in the 10-200meV region on HET spectrometers at ISIS, Rutherford Appleton Laboratory.

Static and dynamic evolution of CO adsorption onγ-U(100)surface with different levels of Mo doping using DFT and AIMD calculations

Alloys of uranium and molybdenum are considered as the future of nuclear fuel and defense materials.However,surface corrosion is a fundamental problem in practical applications and storage.In this study,the static and dynamic evolution of carbon monoxide(CO)adsorption and dissociation onγ-U(100)surface with different Mo doping levels was investigated based on density functional theory and ab initio molecular dynamics.During the static calculation phase,parameters,such as adsorption energy,configuration,and Bader charge,were evaluated at all adsorption sites.Furthermore,the time-dependent behavior of CO molecule adsorption were investigated at the most favorable sites.The minimum energy paths for CO molecu-lar dissociation and atom migration were investigated using the transition state search method.The results demonstrated that the CO on the uranium surface mainly manifests as chemical adsorption before dissociation of the CO molecule.The CO molecule exhibited a tendency to rotate and tilt upright adsorption.However,it is difficult for CO adsorption on the surface in one of the configurations with CO molecule in vertical direction but oxygen(O)is closer to the surface.Bader charge illustrates that the charge transfers from slab atoms to the 2π*antibonding orbital of CO molecule and particularly occurs in carbon(C)atoms.The time is less than 100 fs for the adsorptions that forms embryos with tilt upright in dynamics evolution.The density of states elucidates that the overlapping hybridization of C and O 2p orbitals is mainly formed via the d orbitals of uranium and molybdenum(Mo)atoms in the dissociation and re-adsorption of CO molecule.In conclusion,Mo doping of the surface can decelerate the adsorption and dissociation of CO molecules.A Mo-doped surface,created through ion injection,enhanced the resistance to uranium-induced surface corrosion.

Pseudopotential Density-Functional Calculations for Structures of Small CarbonClusters CN （N=2-8）

We introduce a first-principles density-fumctional theory,i.e.the finite-differcnce pseudopotential density-functional theory in real space and the langevin molecular dynamics annealing technique,to the descriptions of structures and some properties of small carbon clusters(CN,N=2-8).It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.

Strain-controlled graphdiyne membrane for CO2/CH4 separation:First-principle and molecular dynamic simulation

Tensile strain of porous membrane materials can broaden their capacity in gas separation.In this work,using van der Waals corrected density functional theory(DFT)and molecular dynamics(MD)simulations,the performance and mechanism of CO2/CH4 separation through strain-oriented graphdiyne(GDY)monolayer were studied by applying lateral strain.It is demonstrated that the CO2 permeance peaks at 1.29×10^6 gas permeation units(GPU)accompanied with CO2/CH4 selectivity of 5.27×10^3 under ultimate strain,both of which are far beyond the Robeson’s limit.Furthermore,the GDY membrane exhibited a decreasing gas diffusion energy barrier and increasing permeance with the increase of applied tensile strain.CO2 molecule tends to reoriented itself vertically to permeate the membrane.Finally,the CO2 permeability decreases with the increase of the temperature from300 K to 500 K due to conserving of rotational freedom,suggesting an abnormal permeance of CO2 in relation to temperature.Our theoretical results suggest that the stretchable GDY monolayer holds great promise to be an excellent candidate for CO2/CH4 separation,owing to its extremely high selectivity and permeability of CO2.

Linearized Controller Design for the Output Probability Density Functions of Non-Gaussian Stochastic Systems

This paper presents a linearized approach for the controller design of the shape of output probability density functions for general stochastic systems. A square root approximation to an output probability density function is realized by a set of B-spline functions. This generally produces a nonlinear state space model for the weights of the B-spline approximation. A linearized model is therefore obtained and embedded into a performance function that measures the tracking error of the output probability density function with respect to a given distribution. By using this performance function as a Lyapunov function for the closed loop system, a feedback control input has been obtained which guarantees closed loop stability and realizes perfect tracking. The algorithm described in this paper has been tested on a simulated example and desired results have been achieved.

The Effective Chiral Model of Quantum Hadrodynamics Applied to Nuclear Matter and Neutron Stars

We review theoretical relations between macroscopic properties of neutron stars and microscopic quantities of nuclear matter, such as consistency of hadronic nuclear models and observed masses of neutron stars. The relativistic hadronic field theory, quantum hadrodynamics (QHD), and mean-field approximations of the theory are applied to saturation properties of symmetric nuclear and neutron matter. The equivalence between mean-field approximations and Hartree approximation is emphasized in terms of renormalized effective masses and effective coupling constants of hadrons. This is important to prove that the direct application of mean-field (Hartree) approximation to nuclear and neutron matter is inadequate to examine physical observables. The equations of state (EOS), binding energies of nuclear matter, self-consistency of nuclear matter, are reviewed, and the result of chiral Hartree-Fock ?approximation is shown. Neutron stars and history of nuclear astrophysics, nuclear model and nuclear matter, possibility of hadron and hadron-quark neutron stars are briefly reviewed. The hadronic models are very useful and practical for understanding astrophysical phenomena, nuclear matter and radiation phenomena of nuclei.

First-principles calculations on the elastic and thermodynamic properties of NbN

The elastic and thermodynamic properties of NbN at high pressures and high temperatures are investigated by the plane-wave pseudopotential density functional theory （DFT）. The generalized gradient approximation （GGA） with the Perdew-Burke Ernzerhof （PBE） method is used to describe the exchange-correlation energy in the present work. The calculated equilibrium lattice constant a0, bulk modulus B0, and the pressure derivative of bulk modulus B~ of NbN with rocksalt structure are in good agreement with numerous experimental and theoretical data. The elastic properties over a range of pressures from 0 to 80.4 GPa are obtained. Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail. It is indicated that NbN is highly anisotropic in both longitudinal and shear-wave velocities. According to the quasi-harmonic Debye model, in which the phononic effect is considered, the relations of （V - Vo）/Vo to the temperature and the pressure, and the relations of the heat capacity Cv and the thermal expansion coefficient α to temperature are discussed in a pressure range from 0 to 80.4 GPa and a temperature range from 0 to 2500 K. At low temperature, Cv is proportional to T3 and tends to the Dulong Petit limit at higher temperature. We predict that the thermal expansion coefficient α of NbN is about 4.20 × 10-6/K at 300 K and 0 GPa.

Pressure Effect on Elastic and Lattice Dynamic Properties of Beryllium Selenide from First Principles

The lattice dynamic, elastic, and thermodynamic properties of Be Se were investigated with first principles calculations. The phase transition pressure from the zinc blende（B3） to the nickel arsenide（B8） structure of Be Se was determined. The elastic stability analysis suggests that the B3 structure Be Se is mechanically stable in the applied pressure range of 0-50 GPa. Our lattice dynamic calculations show that the B3 structure is lattice dynamically stable under high pressure. Within the quasiharmonic approximation, the thermodynamic properties including the constant volume heat capacity and constant pressure heat capacity are predicted.

从头算分子动力学研究硫脲嘧啶及其互变异构体在低能电子作用下的解离过程

运用玻恩-奥本海默分子动力学模型结合密度泛函理论研究了气相下硫脲嘧啶与低能电子吸附解离动力学过程,发现硫脲嘧啶及其互变异构体在吸附解离过程中一个重要的脱氢现象,即特定位置的化学键N—H键,C—H键断裂,使其在N位点和C位点失去氢原子,形成解离过程中最主要的负离子碎片——闭壳层脱氢负离子(TU-H)-为了更深刻地认识脱氢现象,分别对断裂的化学键进行势能曲线扫描,对键解离能、电子亲和能、负离子(TU-H)-出现势进行计算对比发现,在所有断裂的化学键中N—H键最容易发生断裂,而负离子(TU-H)-的形成主要源于N—H键的断裂.

铝与氮氧化物高温均相反应机理的量子化学计算研究

为了研究Al粉在氮氧化物中的燃烧特性,采用量子化学密度泛函理论ωB97X方法,研究了Al与3种氮氧化物(NO_(2)、NO和N_(2)O)的反应机理。首先,使用ωB97X‑D3方法在def2‑SVP基组水平上优化了各反应物、中间体、过渡态和产物的几何构型,通过频率分析证实中间体和过渡态的真实性,并通过内禀反应坐标(IRC)计算以进一步确定过渡态,得到了详细反应路径和机理。同时,使用双杂化泛函PWPB95结合DFT‑D3校正和def2‑TZVPP基组获得了各结构的单点能,并使用变分插值过渡态理论计算了相关反应的反应速率常数,得出每个反应的阿伦尼乌斯表达式。结果表明,Al与NO和NO_(2)的反应过程为Al与O氧原子连接形成复合物中间体后通过三元环状过渡态破坏N‑O键生成产物;Al与N_(2)O的反应时则为Al与N原子形成复合物后通过四元环状过渡态发生消除反应生成产物。通过分析各反应动力学参数得到Al与NO_(2)、NO和N_(2)O反应活化能分别为:4.3,249 kJ·mol^(-1)和13.4 kJ·mol^(-1)。在2400~4100 K,由于Al与NO_(2)和N_(2)O的反应能垒较低,反应速率均大于106 m^(3)·mol^(-1)·s^(-1),说明该反应容易发生且速率极快,Al与NO的反应能垒极高,因此其逆反应速率远大于正反应速率,且各反应反应速率受温度的影响程度为:NO>N_(2)O>NO_(2)。

高岭石表面水化机理及电场弱化其吸附性能的分子模拟

高岭石是泥岩黏土矿物组成中的主要成分之一,其水理特性对分析高岭石类黏土矿物遇水工程性质劣化的研究至关重要,通过密度泛函理论和分子动力学模拟研究了高岭石表面水化机理及电化学作用对高岭石表面吸附性能的影响。结果表明:水分子在高岭石(001)晶面吸附时水中的Hw、Ow原子与高岭石表面羟基的Hs、Os原子间形成了Hw-Os及Hs-Ow两种类型的氢键,并且Hw-Os氢键作用较强;水分子与高岭石(001)晶面之间形成的氢键作用导致高岭石(001)晶面具有较强的亲水性质;外加电场对体系中水分子的平衡构象及吸附形态产生显著影响,当体系无电场时,水分子通过氢键与高岭石(001)晶面结合紧密,随着电场强度不断增加,水分子逐渐从高岭石表面脱附,以氢原子朝上、氧原子朝下的“V”字型结构向体相中扩散,水分子的偶极矩沿电场方向排列;随着水-高岭石体系中电场强度的增加,吸附体系中的氢键作用逐渐被破坏,水分子脱附能力增强,高岭石表面对水分子的吸附性降低。

ZnO(110)衬底上单层黑磷烯的外延生长

二维黑磷烯作为新一代半导体材料,具有可调带隙和高载流子迁移率等优点,具有广阔的应用前景.但二维黑磷烯目前还不能直接大规模制备,限制了其进一步的研究和应用.分子束外延是一种广泛使用的具有较高外延质量的单晶薄膜生长方法,在制备二维黑磷烯方面具有广阔的应用前景.本文基于密度泛函理论计算筛选了ZnO(110)、GaN(110)、BP(110)和SiC(110)四种潜在的衬底,研究了二维黑磷烯在这些衬底上的生长情况.研究表明,ZnO(110)上的黑磷单层及团簇结构是稳定的,且磷在该表面扩散特性也有助于磷团簇的成核生长.本研究为高效制备二维黑磷烯及其他二维材料提供了有益的指导.

Generalized time-dependent generator coordinate method for induced fission dynamics

The generalized time-dependent generator coordinate method(TD-GCM)is extended to include pairing correlations.The correlated GCM nuclear wave function is expressed in terms of time-dependent generator states and weight functions.The particle–hole channel of the effective interaction is determined by a Hamiltonian derived from an energy density functional,while pairing is treated dynamically in the standard BCS approximation with time-dependent pairing tensor and single-particle occupation probabilities.With the inclusion of pairing correlations,various time-dependent phenomena in open-shell nuclei can be described more realistically.The model is applied to the description of saddle-to-scission dynamics of induced fission.The generalized TD-GCM charge yields and total kinetic energy distribution for the fission of 240Pu,are compared to those obtained using the standard time-dependent density functional theory(TD-DFT)approach,and with available data.

有机给体-受体结构光诱导过程的非绝热动力学模拟:方法与应用

有机太阳能电池的核心组成是有机给体-受体(donor-acceptor,D-A)结构.探究有机给体-受体结构的光激发后的动力学过程对设计新型有机太阳能电池非常重要.非绝热动力学模拟是研究该过程的重要理论方法.然而,相比于小分子体系,有机给体-受体结构通常较为复杂,计算量大,难以采用高精度的非绝热动力学模拟方法.为了克服这一困难,介绍了课题组所发展基于线性响应-含时密度泛函(LR-TDDFT)理论的非绝热动力学模拟方法,通过结合多种分析方法,可以有效的探究有机给体-受体结构光诱导的动力学过程,如电荷转移过程\,能量转移过程\,激子动力学等.该方法不仅可以用于解释现有的实验结果,还可以为后续设计新型有机给体-受体结构提供帮助.