Elucidating linear and nonlinear optical properties of defect chalcopyrite compounds ZnX2Te4 (X=Al,Ga, In) from electronic transitions

We presented a theoretical study of electronic band structure of three compounds ZnAl₂Te₄, ZnGa₂Te₄ and ZnIn₂Te₄ using pseudo potential method within density functional theory. Calculated band structures show that all band gaps are direct with at Γ with values of 1.639eV for ZnAl₂Te₄, 1.026eV for ZnGa₂Te₄and 0.836eV ZnIn₂Te₄. The linear properties based on dielectric function and non-linear optical properties based on second harmonic generation (SHG) were computed. The origin of four critical points (peaks) determined from the second derivative of the imaginary part of the dielectric function is elucidated. The use of individual k-points and individual combination of valence and conduction bands dependent matrix of the dielectric function and the nonlinear optical susceptibility allowed to a precise determination of inter band optical transitions. Indeed, inter-band analysis shows the high intensity of non-linear effect compared to linear effect. Moreover, non-linear inter-band optical transitions involve lower valence bands and higher conduction bands.     

Crystal chemistry of AB2X4 (X = S,Se, Te) compounds

An attempt is made to correlate the crystal structures of ternary chalcogenides of composition AB₂X₄ with the cationic radius ratio and a pseudo force-constant involving their electronegativities. The resultant diagram adequately resolves structures based on the types K₂SO₄, monoclinic, olivine, MnY₂S₄, Th₃P₄, and CaFe₂O₄ but structure types based on spinel, Cr₃Se₄, and Ag₂HgI₄ are not resolved. Crystal chemical arguments are used to explain these observations and to advance reasons for the successes and failures of this method for predicting structure types.     

呋喃同系物C4H4X(X=O,S,Se,Te)三阶非线性光学性质的理论方法比较研究

用ab initio HF，MP2和DFT三种方法的计算结果，根据完全态求和公式自编程序计算了呋喃同系物的三阶非线性光学极化率．结果表明随着杂原子序数的增大，体系的三阶非线性极化率也随着增大，从对称性出发，利用二态模型讨论了体系光学非线性增大的原因．     

Coordination Polyhedra RuXn (X = O,S, Se,Te) in Crystal Structures

Crystal-chemical analysis of 312 compounds containing complexes [Ru _a X _b ] ^z– (X = O, S, Se, Te) is performed using Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres. In most of these complexes, Ru atoms have coordination number (CN) 6 and form RuX₆ octahedra. However, only with respect to oxygen do the Ru(V)–Ru(VII) atoms exhibit CN 5 or 4 with trigonal-bipyramidal and tetrahedral coordination, respectively.The effect of the valence state of the Ru atoms on their stereochemistry is considered. The important role of the Ru–Ru interactions in the structure of the Ru(II)–Ru(V) compounds is established. As a result of the Ru–Ru interactions, the RuX₆ octahedra are linked through a face or common edge or give O₅Ru–RuO_- dimers in which every metal atom occupies one of the vertices of an octahedron formed by the neighboring Ru atom.The dependence of the Ru–Ru and Ru–O bond orders on their lengths is established on the basis of a crystal-structure analysis and the 18-electron rule.     

The RhX n (X = S,Se, Te) Coordination Polyhedra in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were applied to crystal-chemical analysis of all known compounds whose structures contain rhodium atoms surrounded by chalcogen atoms. The influence of the rhodium valence state and the nature of the chalcogen on the main features of Rh stereochemistry are discussed. Rhodium atoms exhibit coordination numbers of 6, 5, or 4 with respect to S, Se, or Te atoms; in addition to the bonds with chalcogens, rhodium can form 1 to 4 bonds with metal atoms. The VDP volume for Rh(III), Rh(2.67), and Rh(II) atoms in selenides and tellurides very weakly depends on the valence state, whereas in the case of sulfides, the volume increases rather regularly with a decrease in the metal oxidation number from Rh(III) to Rh(I).     

The PtX n Coordination Polyhedra (X = S,Se, Te) in Crystal Structures

Using the Voronoi–Dirichlet partition procedure and the method of intersecting spheres, it is demonstrated that in the crystal structures of chalcogen-containing compounds, Pt(IV) atoms form only PtX₆ octahedra (X = S, Se, Te), whereas in the case of Pt(III) and Pt(II), square coordination by X atoms is typical. The Pt(II) atoms can also form PtX₅ square pyramids (X = S, Se), PtS₆ octahedra, and PtTe₃Pt₃ quasi-octahedra in which a platinum atom is located in the trans-position to each coordinated tellurium atom. It was found that Pt(II) atoms in the PtX₄ squares (X = S, Se), unlike square-coordinated Pt(III) atoms, can form one or two Pt–M bonds (M is a d metal) and 1 to 4 secondary Pt–Q bonds, where Q is an s metal or hydrogen. The main features of platinum stereochemistry depending on the metal valence state and coordination number (CN) and on the nature of the chalcogen atom were quantitatively characterized in terms of the Voronoi–Dirichlet polyhedra.     

Theoretical study on structures and stabilities of N4X (X = O,S, Se,Te) series

The stable and transition structures of N₄X (X = O, S, Se, Te) series with singlet state are optimized with the ab initio (MP2) and density functional theory (B3LYP) methods using the 6‐311+G(d) basis set. The ring isomers are found to be the global minima for N₄O, N₄S, N₄Se, and the chain isomer is the minimum for N₄Te. The stabilities are studied by evaluating the dissociation barriers with respect to dissociation. The reactants and products connected by transition structures are determined by applying the intrinsic reaction coordinate (IRC) calculations. The C_2v, C_3v and ring isomers decompose into linear NNX and N₂ molecules, however, the chain isomers decompose into cyclic N₂X and N₂ firstly. A new possible isomerization mechanism between the cyclic and linear structures of N₂X series is studied. The cyclic structures of N₂X convert into linear structures easily with the very low barriers. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Electronic structures and chemical bonding in diatomic ScX to ZnX (X = S, Se, Te)

Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies, and dipole moments of the title molecules in neutral, positively, and negatively charged ions were studied using density functional method. Ground electronic state was assigned for each molecule. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that, besides ionic component, covalent bonds are formed between the metal s, d orbitals, and the p orbital of S, Se, and Te. For neutral and cationic molecules, the covalent character increases from ScX to CrX and from FeX to CuX with an exception of decrease at MnX and ZnX, while for anionic molecules, the trend is not obvious. For both neutral and charged molecules, the sulfides have the shortest bond distance and largest vibrational frequency, while tellurides have the largest bond distance and smallest vibrational frequency. For neutral and anionic molecules, the dissociation energy of sulfides is the largest, that of tellurides is the smallest, while this only remains true for cationic molecules from ScX(+) to FeX(+).     

黄铜矿型半导体材料CuAlX2 (X=S,Se, Te)的电子结构和光学性质

采用基于赝势平面波基组的密度泛函理论方法,研究具有黄铜矿结构的CuAlX2(X=S,Se,Te)晶体的电子结构,并预测了它们的线性和非线性光学性质.结果表明:这些化合物具有相似的能带结构,带隙随X原子从S→Se→Te依次减小.三种晶体的静态介电常数、静态折射率和静态倍频系数d36的变化情况与带隙的变化相反,随着X原子自S→Se→Te改变依次递增,但静态双折射率依次递减.该系列化合物的倍频效应主要来源于价带顶附近的占据能带向以Al和X原子的p电子态为主要成分的空带之间的跃迁.在三种晶体中,CuAlTe2除静态双折射率偏小外,其它光学性能要优于CuAlS2和CuAlSe2.     

The OsX n Coordination Polyhedra (X = O,S, Se,Te) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform a crystal-chemical analysis of compounds whose structures contain Os atoms surrounded by chalcogen atoms. Depending on the valence state, Os atoms bind four to seven X atoms (X = O, S, Se, Te) forming OsX _n coordination polyhedra which can be tetrahedra (n = 4), trigonal bipyramids or square pyramids (n = 5), octahedra (n = 6), or pentagonal bipyramids (n = 7). In some compounds, pairs of OsO₆ octahedra share edges to form Os–Os bonds. The influence of the Os valence state and the nature of the chalcogen atom on the composition and structure of the [Os _a X _b ] groups is discussed. On the basis of analysis of the crystal-structural data from the standpoint of the 18-electron rule, dependences of the Os–O and Os–Os bond orders on the bond lengths are proposed.     

Electronic Structure of Chalcogen Dichlorides ECl2 (E = S,Se, Te)

The electronic structure of the molecules of chalcogen dichlorides ECl₂ (E = S, Se, Te) was investigated by X-ray spectroscopy and quantum-chemical calculations in the X(SW) approximation. The sequence of the energy levels in the ECl₂ molecules was determined. The nature of the bonding in the various orbitals of the molecules in the SCl₂SeCl₂TeCl₂ series was established. The reasons for the reduced chemical stability of the SeCl₂ molecule and the nonexistence of the TeCl₂ molecule in the individual state are indicated.     

Theoretical Comparison of the Bonding in CpCr(CO)2(NX) [X = O,S, Se,Te]

Molecular orbital calculations employing the PM3 model have been used to examine the bonding in the complexes CpCr(CO)₂(NX) (X = O, S, Se, Te). The previously established trend of increasing Cr-N interaction as X changes from O to S is demonstrated by these calculations, and found to extend to Se and Te. Bond lengths, bond orders, vibrational frequencies, and heats of reaction are used to support the conclusion that metal to ligand π-backbonding increases down the periodic chart from NO to NTe.     

Relativistic spin-orbit coupling effects on secondary isotope shifts of (13)C nuclear shielding in CX(2) (X = O, S, Se, Te)

Rovibrational corrections, temperature dependence, and secondary isotope shifts of the (13)C nuclear shielding in CX(2) (X = O, S, Se, Te) are calculated taking into account the relativistic spin-orbit (SO) interaction. The SO effect is considered for the first time for the secondary isotope shifts. The nuclear shielding hypersurface in terms of nuclear displacements is calculated by using a density-functional theory method. Ab initio multiconfiguration self-consistent field calculations are done at the equilibrium geometry for comparison. (13)C NMR measurements are carried out for CS(2). The calculated results are compared with both present and earlier experimental data on CO(2), CS(2), and CSe(2). The heavy-atom SO effects on the rovibrational corrections of (13)C shielding are shown to be significant. For CSe(2) and CTe(2), reliable prediction of secondary isotope effects and their temperature dependence requires the inclusion of the SO corrections. In particular, earlier discrepancies of theory and experiment for CSe(2) are fully resolved by taking the SO interactions into account.     

Nb_3X_4(X=S,Se,Te)的能带结构研究

固相过渡金属原子簇化合物Nb_3X_4(X=S,Se,Te)在低温下出现超导行为,且从S到Te,Nb_3X_4的超导转变温度Tc呈下降趋势。本文采用EHT近似下的紧束缚能带方法,计算了Nb_3X_4的能带结构。讨论其电子结构与超导电性的关系,并从化学键的观点出发对其Tc的递变加以解释。此外,本文还给出了Nb金属晶体的能带结构。     

Silylchalcogenolates MESiR(t)Bu(2) (M = Na, Cu, Zn, Fe; E = S, Se, Te; R = tBu, Ph) and disilyldichalcogenides tBu2RSiE-ESiRtBu2 (E = S, Se, Te; R = tBu, Ph): synthesis, properties, and structures

The sodium silyl chalcogenolates NaESiR(t)Bu(2) (R = Ph, (t)Bu; E = S, Se, Te), accessible by the nucleophilic degradation of S, Se, or Te by the sodium silanides NaSiR(t)Bu(2) (R = Ph, (t)Bu), have been characterized by X-ray structure analysis. Protonolysis of the sodium silyl chalcogenolates yields the corresponding chalcogenols. The Cu and Zn chalcogenolates, [Cu(SSiPh(t)Bu(2))](4) and [ZnCl(SSi(t)Bu(3))(THF)](2), have been synthesized by metathesis reactions of CuCl with NaSSiPh(t)Bu(2) and of ZnCl(2) with NaSSi(t)Bu(3), respectively. The solid-state structures of the transition metal thiolates have been determined. The compounds (t)Bu(2)RSiE-ESiR(t)Bu(2) (R = Ph, (t)Bu; E = S, Se, Te) are accessible via air oxidation. With the exception of (t)Bu(3)SiS-SSi(t)Bu(3), these compounds were analyzed using X-ray crystallography and represent the first structurally characterized silylated heavy dichalcogenides. Oxidative addition of (t)Bu(3)SiTe-TeSi(t)Bu(3) to Fe(CO)(5) yields [Fe(TeSi(t)Bu(3))(CO)(3)](2), which has also been structurally characterized.     

水系锌离子电池嵌入负极材料TiX2 (X = S,Se)的储锌机制

水系锌离子电池(ZIBs)以其低成本、高安全性和环境友好的优点受到了研究者的广泛关注,成为大规模电化学储能系统的理想选择之一。然而锌金属负极在应用时面临着锌枝晶生长、腐蚀反应和副反应等难以克服的障碍,严重制约了水系锌离子电池的发展。探索可替代锌金属的储锌负极是应对上述问题的有效策略,因此研究者围绕过渡金属氧化物、硫化物和导电聚合物开展了深入研究。以TiX₂ (X = S, Se)为代表的二维过渡金属硫族化合物(TMDs)具有较大的层间距和快速的离子传输通道,可作为锌离子电池的负极,但其储锌反应机制尚未得到完整的揭示。在本文中,我们使用密度泛函理论(DFT)计算方法系统地研究锌离子在TiX₂中的嵌入反应。首先我们采用群论去描述嵌锌TiX₂的稳定层间构型的特点,定义了一个依赖于超胞并且只涉及平移旋转两种对称操作的群,其子群可以用来描述层间构型的对称性,而且用来描述最稳定构型的子群总是倾向于有最大的阶数。基于该计算得到的一系列对应于不同放电深度的TiX₂的稳定结构,我们发现TiS₂和TiSe₂两种材料在锌嵌入/脱出过程中的开路电压(OCV)均低于0.5 V。态密度(DOS)的计算结果表明TiX₂具有很好的电子导电性,而分波态密度(PDOS)的结果显示随着锌的嵌入闭壳层的Ti⁴⁺还原成开壳层的Ti³⁺,并且伴随着Zn―X键的生成。Bader电荷分析的结果表明随着X的嵌入,X相比Ti得到了更多的负电荷,意味着X也参与了TiX₂的氧化还原过程。爬坡弹性带方法(CINEB)计算的结果证实了Zn²⁺在TiX₂中具有较低的扩散能垒(对于TiS₂是0.333 eV,对于TiSe₂是0.338 eV)。本文的研究结果不仅从本质上证明了TiX₂适合作为锌离子电池的嵌锌负极材料,而且为其他高性能TMDs电池材料的DFT研究提供了新的见解。     

Density functional study of AuXq (X = O, S, Se, Te, q = +1, 0, -1) molecules

Bond distances, vibrational frequencies, electron affinity, ionization potential, and dissociation energies of the title molecules were studied by use of density functional methods B3LYP, B3P86, B3PW91, BHLYP, BLYP, BP86, mPW1PW91, and PBE1PBE. It was found that the ground electronic state is doublet for neutral species, singlet for the anion, and triplet for the cation, in agreement with experiments and previous theoretical studies. The calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy. The predicted bond distances and vibrational frequencies are in agreement with experiments and previous theoretical results. BP86 and BLYP have relatively good performance in reproducing the experimental results, while BHLYP is the worst functional method compared with the other density functional methods used for the title molecules.     

Synthetic applications of (Me3SiNSN)2E (E = S, Se) in chalcogen-nitrogen chemistry: formation and structural characterization of Cl2TeESN2 (E = S, Se) and [PPh4]2[Pd2(mu-Se2N2S)X4] (X = Cl, Br)

The reaction of (Me3SiNSN)2S with TeCl4 in CH2Cl2 affords Cl2TeS2N2 (1) and that of (Me3SiNSN)2Se with TeCl4 produces Cl2TeSeSN2 (2) in good yields. The products were characterized by X-ray crystallography, as well as by NMR and vibrational spectroscopy and EI mass spectrometry. The Raman spectra were assigned by utilizing DFT molecular orbital calculations. The pathway of the formation of five-membered Cl2TeESN2 rings by the reactions of (Me3SiNSN)2E with TeCl4 (E = S, Se) is discussed. The reaction of (Me3SiNSN)2Se with [PPh4]2[Pd2X6] yields [PPh4]2[Pd2(mu-Se2N2S)X4] (X = Cl, 4a; Br, 4b), the first examples of complexes of the (Se2N2S)2- ligand. In both cases, this ligand bridges the two palladium centers through the selenium atoms.     

Mechanism for linear and nonlinear optical effects in KBe2BO3F2 (KBBF) crystal

Electronic structure calculations of KBe₂BO₃F₂ crystal from first principles have been performed based on a plane-wave pseudopotential method for the first time. Its optical linear and second harmonic generation (SHG) coefficients are also calculated. The SHG coefficient measured early was much higher than that of our calculation, however, recent experiment confirms our calculated results. Moreover, a real-space atom-cutting method is adopted to analyze the respective contributions of the cation and anionic group to optical response. The results show that the contributions to the SHG coefficients from the (BO₃)³⁻ and (BeFO₃)⁵⁻ groups are dominant and comparable.