Relativistic density functional investigation of UX6（X=F,Cl,Br and I）

The molecular structures and the vibrational frequencies of uranium hexahalides UX 6(X=F,Cl,Br and I) molecules are investigated by using local density approximation(LDA) and generalised gradient approximation(GGA) functions(BP,BLYP and RPBE) in combination with two different relativistic methods(scalar and scalar+spin-orbit relativistic effects).The calculated results show that the differences are trivial between scalar and scalar+spin-orbit relativistic methods.The vibrational frequencies are also compared with existing experimental values,and overall,the RPBE approach gives the smallest error.The bond dissociation energies(BDEs) of UX 6 are computed by using the RPBE function,thereby obtaining exact vibrational frequencies.In addition,the calculated magnitudes of the spin-orbit effect on the BDE of UX 6(X=F,Cl,Br,and I) are found to be approximately-0.3198,-0.3218,-0.3609 and-0.4415 eV,respectively.     

The structural and spectroscopic properties for uranium oxides

The equilibrium structures, the charge population, and the spectroscopic properties of UO, UO 2 , UO 3 , and U 2 O 3 molecules are systematically investigated using the density functional theory (DFT) with the method of generalized gradient approximation (GGA). The bond lengths and the vibrational frequencies of the ground states of UO, UO 2 , and UO 3 molecules are all in agreement with available experimental data. For U 2 O 3 molecules, our calculations indicate that the ground state of the U 2 O 3 molecule is an X 7 A ′ 1 state with D 3h (trigonal bipyramid) symmetry (R 1 (U–O)=0.2113 nm, R 2 (U 1 –U 2 )=0.2921 nm, ∠U 1 OU 2 = 87.5 , dihedral angle Θ(U,O 1 ,O 2 ,O 3 )=62.40 ). The harmonic frequency, the IR intensity and the spin density of the U 2 O 3 molecule are all obtained for the first time in theory. For the ground state of U 2 O 3 molecules, the vibrational frequencies are 178.46 (A ′ 1 ), 276.79 (E ′′ 1 ), 310.77 (E ′ 1 ), 396.63 (A ′′ 2 ), 579.15 (E ′ 1 ), and 614.98 (A ′ 1 ) cm 1 . The vibrational modes corresponding to the IR maximum peaks are worked out for UO 3 and U 2 O 3 molecules. Besides, the results of Gophinatan–Jug bond order indicate that UO, UO 2 , and UO 3 molecules possess U=O double bonds and that the U 2 O 3 molecule possesses U–O single bonds and a U–U single bond.     

GaSi_n(n=1-6)团簇结构和稳定性的第一性原理研究

采用密度泛函理论(DFT),在B3LYP/6-311+G(d)水平下研究了GaSi_n(n=1-6)团簇的几何构型、电子性质、稳定性和振动特性.研究结果表明:GaSi_n(n=1-6)团簇基态结构基本保持了纯硅团簇的结构框架,Ga原子往往被吸附在Sin团簇的表面上.布局分析显示电子由Ga原子向Sin框架转移.平均束缚能和分裂能表明GaSi_3和GaSi_5团簇相对其他团簇具有较强的稳定性.振动特性研究表明:GaSi_n(n=1-6)团簇的IR活性最强振动模式主要是Ga原子与Sin结构之间的相对振动.极化率的研究表明,随着Si原子数的增多,GaSi_n团簇的非线形光学效应逐渐增强,更容易被外场极化.     

Infrared spectra and structure of tetravalent uranium chloride nanoclusters in electron-donor solvents

We have studied the IR absorption spectra of tetravalent uranium chlorides in electron-donor solvents. We discuss the changes in these spectra on coordination of the solvent molecules to the tetravalent uranium. We consider the participation of water molecules in this process. On this basis, we draw the conclusion that clusters form with coordination number equal mainly to six. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 729–732, September–October, 2008.     

Electronic and magnetic properties of single 3d-transition metals adsorbed on anthracene: a relativistic density functional theory study

Within the framework of relativistic density functional theory in the regime of generalised gradient approximation, we have obtained magnetic properties of single 3d-transition metal atoms (from Sc to Ni) adsorbed on anthracene molecule. Binding energies, local spin and orbital magnetic moments, and magnetic anisotropy energies were determined. Our calculations show that all 3d-transition metal atoms bind to anthracene molecule in the presence of spin–orbit coupling. We have found these complexes are spin-polarised and soft magnet.     

The stability of an isentropic model for a gaseous relativistic star

We show that the isentropic subclass of Buchdahl’s exact solution for a gaseous relativistic star is stable and gravitationally bound for all values of the compactness ratio u [≡ (M/R), where M is the total mass and R is the radius of the configuration in geometrized units] in the range, 0 <  u ≤  0.20, corresponding to the regular behaviour of the solution. This result is in agreement with the expectation and opposite to the earlier claim found in the literature.     

High-level theoretical spectroscopic parameters for three ions of astrochemical interest

The equilibrium geometry and rovibrational spectroscopic parameters of the three astrochemical ions l-C₃H⁺, l-SiC₂H⁺, and C₃N^? and some of their isotopologues are obtained from high-level quantum chemical calculations. A composite approach based on the explicitly correlated coupled-cluster method CCSD(T)-F12b, that further includes core correlation, scalar-relativistic effects and most importantly higher order correlation beyond CCSD(T) is used to set-up the near-equilibrium potential energy surface (PES). The spectroscopic parameters of these linear tetra-atomic ions are then extracted from these PESs by vibrational perturbation theory of second order (VPT2). Calculation of absolute intensities is also carried out for the stretching frequencies of the cations in order to identify the bands that are most likely to be detected. The importance of the accurate calculation of the rotational constants B₀ and D₀ for astrochemistry is discussed as well as the limits of VPT2 in this context and reasons for these limitations.     

Effects of the substrate on graphone magnetism: A density functional theory study

The magnetism of graphone, a single-side-hydrogenated graphene derivative, has been related to the localized and unpaired p-electrons associated with the unhydrogenated carbon atoms. In the present density functional theory study, the effects the adhesion to either Cu(111) or α-quartz (0001) surface on the magnetic properties of graphone have been investigated. The total magnetization of the graphone adsorbed to copper and quartz surface is reduced by four and two times, respectively, with respect to the isolated graphone. We have shown there is electronic charge transfer from surface towards three-fold coordinated C atoms of graphone, but the main role in the partial magnetism quenching is played by bond formation and the consequent electron pairing of p-electrons. The critical temperature has been investigated on the basis of the mean field theory to evaluate the stability of the magnetism at ordinary temperature.     

CN bond orientation in metal carbonitride endofullerenes:A density functional theory study

The geometric and electronic structures of scandium carbonitride endofullerene Sc_3CN@C_(2n)(2 n = 68, 78, 80, 82,and 84) and Sc(Y)NC@C_(76) have been systematically investigated to identify the preferred position of internal C and N atoms by density functional theory(DFT) calculations combined with statistical mechanics treatments. The CN bond orientation can generally be inferred from the molecule stability and electronic configuration. It is found that Sc_3CN@C_(2n) molecules have the most stable structure with C atom locating at the center of Sc3 CN cluster. The CN bond has trivalent form of [CN]~(3-)and connects with adjacent three Sc atoms tightly. However, in Sc(Y)NC@C_(76) with [NC]~-, the N atom always resides in the center of the whole molecule. In addition, the stability of Sc_3CN@C_(2n)has been further compared in terms of the organization of the corresponding molecular energy level. The structural differences between Sc_3CN@C_(2n) and Sc_3NC@C_(2n)are highlighted by their respected infrared spectra.     

High-resolution infrared and theoretical study of gaseous 1,2,5-selenadiazole in the 600-1400 cm range

The Fourier transform gas-phase IR spectrum of natural isotopic 1,2,5-selenadiazole, C₂H₂N₂Se, has been recorded with a resolution of ca. 0.0025 cm⁻¹ in the wavenumber region 600-1400 cm⁻¹. The three a-type bands, ν₂ (A₁), ν₄ (A₁), ν₅ (A₁), the two b-type bands ν₁₁ (B₁), ν₁₂ (B₁), and the c-type band ν₁₄ (B₂) for each of the isotopologues C₂H₂N₂⁸⁰Se and C₂H₂N₂⁷⁸Se have been analyzed using the Watson model. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. The rotational constants, harmonic and anharmonic frequencies, and vibration-rotation constants (alphas, ) have been predicted by quantum chemical calculations using a cc-pVTZ basis at the MP2 and B3LYP methodology levels, and compared with the present experimental data. Although the rotation constants are marginally closer to experiment from the MP2 calculations, in general the B3LYP frequencies and alphas are closer to experiment.     

High-resolution infrared and theoretical study of gaseous oxazole in the 600-1400 cm region

The Fourier transform gas-phase IR spectrum of oxazole, C₃H₃NO, has been recorded with a resolution of ca. 0.0030 cm⁻¹ in the wavenumber region 600-1400 cm⁻¹. The rotational structures of 10 fundamental bands (four of a-type, three of b-type and three of c-type) have been analysed using the Watson model. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. A number of perturbations have been identified in the bands. From a local crossing observed in ν₁₅ we located the very weak ν₁₄ band at 858.19(1) cm⁻¹. Also ν₁₃ is definitively located at 899.3 cm⁻¹. The three global c-Coriolis interacting dyads ν₉/ν₁₀, ν₁₀/ν₁₁, and ν₁₂/ν₁₃ have each been analysed by a model including first and second order Coriolis resonance using ab initio predicted first order Coriolis coupling constants; second order Coriolis interaction parameters are determined. The rotational constants, harmonic and anharmonic frequencies, intensities, and vibration-rotation constants (alphas, ) have been predicted by quantum chemical calculations using a cc-pVTZ basis at the MP2 and B3LYP methodology levels, and compared with the present experimental data. Both the rotational constants and frequencies are marginally closer to experiment from the B3LYP calculations. In order to make more significant comparisons between theory and experiment for the alphas, we take differences between ground and vibronic state values; under these circumstances, the B3LYP definitely have a closer fit to experiment.     

磺胺甲恶唑的振动光谱和密度泛函理论研究

磺胺甲恶唑(Sulfamethoxazole, SMX)是一种磺胺类广谱抗生素.基于密度泛函理论(DFT)的B3LYP方法,在B3LYP/6-311++G (d, p)基组水平上对SMX初始构型进行结构优化,得出该分子最稳定结构构型.同时,给出了SMX的键长、键角和二面角等空间结构参数值,确定该分子空间构型为非平面结构.相同基组水平下进行频率计算,通过频率校正因子0.9630修正并绘制了SMX分子的红外光谱和拉曼光谱图.发现光谱谱段主要分布在3600-2800 cm^-1和1700-300 cm^-1频率段,并且理论计算值和实验测定值有较好吻合,表明DFT计算方法是可取和可信的.借助GaussView 6.0软件和计算得到的势能分布结果对频率范围内每一个振动模式进行了指认归属.此外,采用Multiwfn和VMD程序计算并分析SMX分子的静电势和前线分子轨道,预测了该分子的反应活性位点.该结果为SMX分子的振动光谱检测提供基础数据,为其结构鉴定提供技术参考.     

密度泛函理论研究SiCmN团簇

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对SiCmN(m=1-7)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=1~5的团簇为线状结构,m=6、7的团簇为环状结构。m增大过程中,线状团簇自旋多重度均为2,而环状团簇出现2、4和6自旋多重度。能量的二次差分值表明m为奇数的团簇比m为偶数的更为稳定。     

密度泛函理论研究SiCmN团簇

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对SiCmN(m=1-7)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=1~5的团簇为线状结构,m=6、7的团簇为环状结构。m增大过程中,线状团簇自旋多重度均为2,而环状团簇出现2、4和6自旋多重度。能量的二次差分值表明m为奇数的团簇比m为偶数的更为稳定。     

A density functional study of plutonium dioxide

The electronic and geometric structures of bulk PuO₂ and its (110) surface have been studied using a periodic model within the generalized gradient approximation (GGA) of density functional theory (DFT). The sixty core electrons of the Pu atom have been represented by a relativistic effective core potential and scalar relativistic effects have been incorporated on the valence orbitals. For bulk PuO₂, we predict an equilibrium lattice constant of 10.10 a.u. and a cohesive energy of 17.28 eV, in good agreement with experimental data. For the (110) surface, upon relaxation, the distance between the top layer and the next layer is found to decrease by 0.12 ?, i.e. 5.3% of the corresponding interlayer distance in the bulk. The distance between the two oxygen atoms on the top layer is found to increase by 0.15 ?, i.e. 5.6% of the corresponding bulk value. The small surface relaxation energy of 0.268 eV per unit cell indicates the fair stability of this surface. The effective charges on Pu and O atoms show that the chemical bonding in this system is not purely ionic. Together with the metallic feature of the density of states (DOS) on the surface, the effective charge distribution provides some basis for understanding surface reactivity and corresponding support for catalysis. Received 16 June 2000     

A study of transverse charge density of pions in relativistic quantum mechanics

The transverse charge density of pions is calculated based on relativistic quantum mechanics, where the pion is regarded as a quark-antiquark bound state. Corrections from the two spin-1/2 constituents and from the wave function of a quark and antiquark inside the bound system are discussed. The calculated results are compared to the results with a realistic effective Lagrangian approach as well as to that with a simple covariant model where the pion is regarded as a composite system with two scalar particles.     

氘、氚代聚苯乙烯单体abinitio研究

用HF,MP2及BLYP从头算方法,在6—31G基组水平上,优化了聚苯乙烯单体基态的平衡几何构型.主要用BLYP6—31方法研究了氘、氚代聚苯乙烯单体(DPS,PST)的正则振动频率、红外光谱强度、C—D键键能,并对正则振动模式进行了简单分析,同时研究了DPS,PST单体中温度、压强与熵的关系. 关键词： 平衡几何构型 正则振动频率 红外光谱强度 键能     

A study of the molecular structure of DL-serine with the method of low-temperature IR spectroscopy

Use of low-temperature IR spectroscopy in studies of compounds with a developed system of hydrogen bonds such as DL-serine revealed a complete set of vibrational frequencies. The region of manifestation of stretching vibrations of OH groups involved in the formation of strong hydrogen bonds was found. It is shown experimentally that in a crystal some of the molecules of SL-serine exist in the nonionized form. On the basis of analysis of experimental data, frequency ranges of stretching deformation and torsional vibrations of NH ₃ ⁺ , COO⁻, and OH groups were determined more accurately. It is found that in the crystals there exist molecules of DL-serine with different spatial orientation of NH ₃ ⁺ COO⁻, and COH groups. It is shown that conformational diversity of molecular structures is also preserved at T=18 K. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 864–868, November–December, 1998.