Study the Structural, Electronic, Optical Properties of CZTS Compound after Doping Ba at Zn Site and Si at Sn Site Using Density Functional Theory (DFT)

The structural, electronic, and optical properties of Cu2Zn1−xBaxSn1−ySiyS4 compounds have been calculated using GGA-PBE function within the framework of Density Functional Theory (DFT). In the present work, lattice parameters remained the same, that is tetragonal crystal structure for 0% and 100% doping concentration. The electronic band gap of Cu2Zn1−xBaxSn1−ySiyS4 compounds has been gradually increased for continuous increment of doping concentration where the highest electronic band gap is 1.117 eV for Cu2BaSiS4 structure. Moreover, the band gap changes from direct to indirect band gap with the increase of doping concentration in the parent compound. The absorption coefficient has been found to be high (> 104 cm−1) in UV-region for all the doping concentration which makes the studied compound as a potential candidate of absorber layer in the UV detector. The theoretical study of the effect of double doping in the CZTS compound is very interesting for improving the quality of it and it would be a reference for the theoretical and experimental researchers.

Calculation of microscopic nuclear level densities based on covariant density functional theory

In this study,a microscopic method for calculating the nuclear level density(NLD)based on the covariant density functional theory(CDFT)is developed.The particle-hole state density is calculated by a combinatorial method using single-particle level schemes obtained from the CDFT,and the level densities are then obtained by considering collective effects such as vibration and rotation.Our results are compared with those of other NLD models,including phenomenological,microstatisti-cal and nonrelativistic Hartree–Fock–Bogoliubov combinatorial models.This comparison suggests that the general trends among these models are essentially the same,except for some deviations among the different NLD models.In addition,the NLDs obtained using the CDFT combinatorial method with normalization are compared with experimental data,including the observed cumulative number of levels at low excitation energies and the measured NLDs.The CDFT combinatorial method yields results that are in reasonable agreement with the existing experimental data.

白铅矿(PbCO_(3))和菱锌矿(ZnCO_(3))硫化机理的DFT研究

采用密度泛函理论(DFT)比较研究白铅矿(PbCO_(3))和菱锌矿(ZnCO_(3))硫化机理的差异。通过在PbCO_(3)/ZnCO_(3)表面构建Pb-S/Zn-S层来模拟硫化结构。层距和Mulliken电荷的结果表明,PbCO_(3)上形成稳定的Pb-S层,而ZnCO_(3)上形成的Zn-S层不稳定。由于Pb-S层具有高的共价性,而Zn-S层具有高的离子性,因此,硫化-黄药法对PbCO_(3)浮选有效,对ZnCO_(3)浮选无效。为了回收ZnCO_(3),需要强离子性捕收剂,因此,硫化-胺法在ZnCO_(3)浮选中应用较广。PbCO_(3)和ZnCO_(3)表面硫化层结构和浮选行为差异主要是由于金属离子(Pb^(2+)和Zn^(2+))和配体(O配体和S配体)极化率的不同以及Zn^(2+)3d^(10)轨道的惰性造成的。

LiODFP在锂离子电池正极氧化分解的DFT研究

使用密度泛函理论(DFT),研究锂盐二氟二草酸磷酸锂(LiODFP)作为成膜添加剂在锂离子电池正极的作用机理。各研究体系的氧化电势理论计算值的排列顺序为:碳酸酯(包括EC、PC、EMC和DMC)>ODFP^(-)(单分子)≈碳酸酯-ODFP^(-)配合物。ODFP^(-)优先于碳酸酯发生氧化反应,ODFP^(-)结构分解的路径比EC分子分解的路径更容易进行。EC+ODFP^(-)-e体系可能发生的分解反应路径是ODFP^(-)结构开环,生成CO、CO_(2)和自由基R1。R1可能进一步发生自由基终止反应,生成含有氟代磷酸盐单体的低聚物,从而抑制碳酸酯溶剂分子的氧化分解。

Direct atomic-level insight into oxygen reduction reaction on size-dependent Pt-based electrocatalysts from density functional theory calculations

Developing novel oxygen reduction reaction(ORR)catalysts with high activity is urgent for proton exchange membrane fuel cells.Herein,we investigated a group of size-dependent Pt-based catalysts as promising ORR catalysts by density functional theory calculations,ranging from single-atom,nanocluster to bulk Pt catalysts.The results showed that the ORR overpotential of these Pt-based catalysts increased when its size enlarged to the nanoparticle scale or reduced to the single-atom scale,and the Pt_(38)cluster had the lowest ORR overpotential(0.46 V)compared with that of Pt_(111)(0.57 V)and single atom Pt(0.7 V).Moreover,we established a volcano curve relationship between the ORR overpotential and binding energy of O*(ΔE_(O*),confirming the intermediate species anchored on Pt38cluster with suitable binding energy located at top of volcano curve.The interaction between intermediate species and Pt-based catalysts were also investigated by the charge distribution and projected density of state and which further confirmed the results of volcano curve.

SO_(2)对K2CO_(3)吸附CO_(2)性能影响的实验及DFT机理研究

电站锅炉的尾气在脱硫后含有微量的SO_(2),导致CO_(2)吸附剂性能变差。根据电厂烟气的组分,采用模拟烟气在实验室条件下对K2CO_(3)吸附剂的CO_(2)吸附性能及SO_(2)对CO_(2)吸附的影响进行实验研究。结合XRD分析,利用密度泛函理论(density functional theory,DFT)对SO_(2)在K2CO_(3)吸附剂上的影响及CO_(2)吸附机理进行理论研究。结果表明,受SO_(2)分子S原子活跃的s轨道影响,S的p轨道及O原子活性均增强,与K2CO_(3)表面O原子价带顶能带简并,SO_(2)被优先吸附在K2CO_(3)表面的O顶位,并将CO_(2)推离吸附剂表面,导致吸附剂活性位点虽有空余却无法吸附CO_(2)。在实验中表现为:模拟烟气中CO_(2)体积浓度为10%时,气氛中体积浓度为0.007%的SO_(2)会使吸附剂的吸附量由1.65 mmol/g降低至1.01 mmol/g。提出CO_(2)与H2O在K2CO_(3)(001)表面的吸附机理,理论计算的反应活化能为40.7 kJ/mol,反应热为-54.9 kJ/mol。

Understanding the Relativistic Generalization of Density Functional Theory (DFT) and Completing It in Practice

In 2014, 50 years following the introduction of density functional theory (DFT), a rigorous understanding of it was published [AIP Advances, 4, 127,104 (2014)]. This understanding includes two features that complete the theory in practice, inasmuch as they are necessary for its correct application in electronic structure calculations;this understanding elucidates what appears to have been the crucial misunderstanding for 50 years, namely, the confusion between a stationary solution, attainable with most basis sets, following self-consistent iterations, with the ground state solution. The latter is obtained by a calculation that employs the well-defined optimal basis set for the system. The aim of this work is to review the above understanding and to extend it to the relativistic generalization of density functional theory by Rajagopal and Callaway [Phys. Rev. B7, 1912 (1973)]. This extension straightforwardly follows similar steps taken in the non-relativistic case, with the four-component current density, in the former, replacing the electronic charge density, in the latter. This new understanding, which completes relativistic DFT in practice, is expected to be needed for the study of heavy atoms and of materials (from molecules to solids) containing them—as is the case for some high temperature superconductors.

表面活性剂在气液界面层性质的DFT理论研究

在温度273.15 K、压力1.013×10^(5) Pa条件下,该文采用密度泛函理论计算方法,应用Gaussian 03程序B3LYP方法6-31G基组对十二烷基二甲基氧化胺及十二烷基磺酸钠的水合物结构(水分子数n=1~3)进行了全优化计算,从分子水平上研究了在气液界面层中表面活性剂分子与水之间的相互相用,并对界面的形成、稳定性和影响因素进行了分析.分析结果表明:表面活性剂与水分子以氢键形成了稳定的水合物,在水合物中发生明显的电荷从表面活性剂分子向水分子的迁移现象,水合过程体系的吉布斯自由能降低,是一个自发的过程.通过计算水合物的电荷分布规律,对气液界面层表面活性剂分子间相互作用及排布方式进行了理论研究.研究结果表明:表面活性剂疏水基团与亲水基团连接部分带有与亲水基同种电荷,而远离亲水基的一端带有部分负电荷;气液界面层表面活性剂可以通过氢键及静电作用力形成稳定有序的排布.对十二烷基二甲基氧化胺及十二烷基磺酸钠复配协同增效作用进行了理论解释,表面活性剂水合物分子间除了氢键作用外,还存在较强的正负电荷静电作用力,从而提高了其界面稳定性.

水溶液环境下手性配合物Phe·Ca^(2+)对映异构机理的DFT研究

采用DFT(density functional theory)的M06-2X、MN15方法和处理溶剂效应的SMD模型方法,研究了水溶液中S-苯丙氨酸(S-Phe)与二价钙(Ca^(2+))配合物(Phe·Ca^(2+))的对映异构。反应通道研究发现,S-Phe·Ca^(2+)的对映异构可在质子以N和O分别为桥以及O和N联合为桥迁移的3个通道上实现。计算表明:最优势通道是质子以N为桥迁移,隐性水溶剂效应下决速步自由能垒是227.5 kJ/mol,显性水溶剂效应下该能垒降至108.0~117.6 kJ/mol。结果表明:水溶液中手性Phe·Ca^(2+)的消旋过程十分缓慢,将其用于生命体同补苯丙氨酸和钙元素可能比较安全。

水液相下苯丙氨酸钾配合物对映异构的DFT研究

采用DFT(密度泛函理论)的M06-2X、MN15方法和处理溶剂效应的SMD模型方法,研究了水液相环境下手性苯丙氨酸钾配合物(Phe·K^(+))的对映异构。研究发现:手性Phe·K^(+)的对映异构可在质子只以氧为桥、以氧和氮联合为桥和只以氮为桥迁移的3个通道上实现。计算表明:质子只以氮为桥迁移是最优势反应通道,隐性水溶剂效应下决速步的自由能垒是220.0 kJ/mol,显性水溶剂效应下该能垒降到114.0至122.8kJ/mol之间。结果表明:水液相下手性Phe·K^(+)的消旋反应过程十分缓慢,苯丙氨酸钾短期用于生命体同补苯丙氨酸和钾元素比较安全。

Effect of N-substituents on performance of thiourea collectors by density functional theory calculations

Using density functional methods,some properties were studied such as the energies and compositions of frontier molecular orbitals and the atomic charges,which are related to the reactive behavior of thioureas containing different N-substituent groupings.The calculation results indicate that the N-substituent groupings have significant effect on the flotation performance of thiourea collectors.The order of electron-donating ability is N-propyl-N'-benzyl-thiourea(PBZYTU)>N-propyl-N'-ethyl-thiourea (PETU)>N-propyl-N'-allyl-thiourea(PALTU)>>N-propyl-N'-acetyl-thiourea(PACTU)>N-propyl-N'-ethoxycarbonyl-thiourea (PECTU)>N-propyl-N'-benzoyl-thiourea(PBZOYTU),and the order of feedback-electron-accepting ability is PBZOYTU> PACTU>PECTU>>PALTU>PETU>PBZYTU.This implies that PBZOYTU,PACTU or PECTU can react with copper atoms having(t2g) 6 (eg) 3Cu(II)or t 6e 4Cu(I)configuration on the surfaces of copper sulfide minerals through normal covalent bond and back donation covalent bond,and exhibit excellently collecting performance for copper sulfide minerals.These are consistent with the experimental data reported in the literatures.

水液相下Phe分子与Na^(+)配合物对映异构的DFT研究

该文采用DFT(密度泛函理论)的M06-2X、MN15方法和处理溶剂效应的SMD模型方法,研究了在水液相下苯丙氨酸与钠离子配合物(Phe•Na^(+))的对映异构.研究结果发现:手性Phe•Na^(+)的对映异构可在质子只以氧为桥、以氧和氮联合为桥和只以氮为桥迁移的3个通道上实现.反应势能面计算结果表明:质子只以氮为桥迁移的反应通道最优势,其余2个反应通道处于劣势.在隐性水溶剂效应下优、劣通道的速度决定步骤的自由能垒分别为228.0和255.8 kJ•mol^(-1),在显性水溶剂效应下优、劣通道的速度决定步骤的自由能垒分别降至111.7~122.0 kJ•mol^(-1)和142.2~145.8 kJ•mol^(-1).研究结果表明:在水液相下手性Phe•Na^(+)的消旋速度极慢,苯丙氨酸钠短期用于生命体同补苯丙氨酸和钠元素比较安全.

Prediction of Aqueous Solubility for 209 Polychlorinated Diphenyl Ethers from Molecular Structural Parameters by DFT Method

Optimized calculations of 209 polychlorinated diphenyl ethers （PCDEs） and diphenyl ethers were carried out at the B3LYP/6-31G^＊ level with the Gaussian 98 program. Based on the theoretical linear solvation energy relationship （TLSER） model, the obtained structural parameters were taken as theoretical descriptors to establish the novel QSPR model for predicting aqueous solubility （-lgSw） of PCDEs. The model obtained in this work contains two variables： mean molecular polarizability （a） and the most positive partial charge on a hydrogen atom （qH^＋）, of which RE = 0.9606 and SD = 0.32. And the results of cross-validation test also show that the model exhibits optimum stability and better predictive power. Moreover, the predictive power of the new model is better than that of MCIs method.

A Periodic Density Functional Study on Adsorption Properties of Methoxy on Au(111) Surface

Adsorption of CH3O at four sites （top, bridge, hcp, fcc） on Au（111） surface has been investigated by density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies, structures, Mulliken charges and vibrational frequencies of CH3O on Au（111） surface with full-geometry optimization. The predicted results are compared with the available experimental observation. The calculated CH3O adsorption structure and stretching vibrational frequencies agree well with experimental ones, and precise determinations of adsorption sites are carded out. The most favorite adsorption on Au（111） occurs at the bridge site, and O-C axis is tilted to the surface. However, on hollow sites （hcp, fcc） the species is adsorbed in an upright geometry （pseudo-C3v local symmetry）.

Interaction of Photoactive[Fe(CN)_6]^(4-) with TiO_2 Anatase(101) Surface:A Periodic Density Functional Theory Study

The plane-wave pseudopotential function method, based on density-functional theory, has been used to calculate the adsorption, electronic band structures, orbitals and optical absorption spectrum of [Fe（CN）6]^4- on TiOz anatase（101） surface. Our calculations reveal that the surface-modified anatase system has large adsorption energy and a much narrower band gap. [Fe（CN）6]^4- adsorption on the （101） surface could lead to a large red shift of the anatase optical absorption threshold, which extends into a visible region significantly. The calculated results are in agreement with the experiment and other theoretical studies reasonably. It is very important for the understanding and further development ofphotovoltaic materials that are active under visible light.

Studies of n-Octanol/water Partition Coefficients (lgK_(ow)) for Organophosphate Compounds by Density Functional Theory

Optimized calculation of 35 dialkyl phenyl phosphate compounds （OPs） was carded out at the B3LYP/6-31G^＊ level in Gaussian 98 program. Based on the theoretical linear solvation energy relationship （TLSER） model, the obtained parameters were taken as theoretical descriptors to establish the novel QSPR model for predicting n-octanol/water partition coefficients （lgKow） of OPs. The new model achieved in this work contains three variables, i.e., molecular volume （Vm）, dipole moment of the molecules （μ） and enthalpy （H^0）. For this model, R^2 = 0.9167 and SD = 0.31 at large t values. In addition, the variation inflation factors （VIF） of variables are all close to 1.0, suggesting high accuracy of the predicting model. And the results of cross-validation test （q^2 = 0.8993） and method validation also showed the model of this study exhibited optimum stability and better predictive power than that from semi-empirical method. The model achieved can be used to predict IgKow of congeneric compounds.

Joint probability density function of the stochastic responses of nonlinear structures

The joint probability density fimction （PDF） of different structural responses is a very important topic in the stochastic response analysis of nonlinear structures. In this paper, the probability density evolution method, which is successfully developed to capture the instantaneous PDF of an arbitrary single response of interest, is extended to evaluate the joint PDF of any two responses. A two-dimensional partial differential equation in terms of the joint PDF is established. The strategy of selecting representative points via the number theoretical method and sieved by a hyper-ellipsoid is outlined. A two-dimensional difference scheme is developed. The free vibration of an SDOF system is examined to verify the proposed method, and a flame structure exhibiting hysteresis subjected to stochastic ground motion is investigated. It is pointed out that the correlation of different responses results from the fact that randomness of different responses comes from the same set of basic random parameters involved. In other words, the essence of the probabilistic correlation is a physical correlation.

Hydrogen storage in BC_3 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 BC3 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 BC3 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.

Thermodynamic Properties for Polybrominated Dibenzothiophenes by Density Functional Theory

The thermodynamic properties of 135 polybrominated dibenzothiophenes （PBDTs） in the gaseous state at 298.15 K and 1.013×10^5 Pa, are calculated using the density functional theory （the B3LYP/6-311G^＊＊） with Gaussian 03. Based on these data, the isodesmic reacflons are designed to calculate the standard enthalpy of formation （△fH^θ） and the standard Gibbs energy of formation （△fG^θ） of PBDTs. The relations of these thermodynamic parameters with the number and positionof bromine subsfituents （NPBS） are discussed, and it is found that there exist good correlations between othermody namic parameters （including heat capacity at constant volume, entropy, enthaipy, free energy, △fH^θ, △fG^θ） and NPBS. Thoe relative stability order of PBDT congeners is proposed theoretically based on the relative magnitude of their △fG^θ. In addition, the values of molar heat capacities at constant pressure （Cp,m） for PBDT c ongelaers are calculated.

Density Functional Theory Study on the Adsorption of Dioxygen on Small Pt-Pd Clusters

The electronic and physical properties of PtmPdn （m＋n≤5） metal clusters and their interactions with dioxygen have been studied by using hybrid density functional B3LYP method. The total energies, atomization energies, vibration frequencies, and charge distributions were reported. The Pt-Pt bridge site modified by Pd atoms was found to be the most active site for the dissociation of dioxygen, which was mainly due to the change of electronic structures of the Pt atoms in bimetallic Pt-Pd clusters.