不同初始振动态下D2O在B带的态-态光解动力学

利用高精度的非绝热从头算势能面,采用量子实波包方法研究了D₂O在3个不同初始振动态(0,1,0)、(1,0,0)和(0,0,1)下光激发到~B态解离过程的态-态量子动力学．结果表明,由于初始振动波函数的形状不同,从不同振动态产生的吸收光谱、产物分布和产物分支比具有不同的动力学特性．弯曲振动态(010)的吸收谱呈现出两波瓣的形状且中间具有较浅的极小值,其基态产物OD( ~X)在高能量区域会出现轻微的振动态反转现象．所有初始振动态得到的激发态产物OD(_?)的振-转态分布都随能量的变化出现强烈的震荡,这是由于受到了激发态势能面上长寿命共振态的影响．反对称伸缩振动态(0,0,1)在高能量区域具有较大的产物分支比OD(_?)/OD( ~X),表明绝热通道在某些情形下是主要的解离通道．     

Highly accurate coupled-cluster singlet and triplet pair energies from explicitly correlated calculations in comparison with extrapolation techniques

Coupled-cluster singles and doubles (CCSD) valence shell correlation energies of the systems CH₂ (<¹A₁ state), H₂O, HF, N₂, CO, Ne, and F₂ are computed by means of standard calculations with correlation-consistent basis sets of the type cc-pVxZ (x = D, T, Q, 5, 6) and by means of explicitly correlated coupled-cluster calculations (CCSD-R12/B) with large uncontracted basis sets of the type 19s14p8d6f4g3h for C, N, O, F, and Ne and 9s6p4d3f for H. These CCSD-R12/B calculations provide reference values for the basis set limit of CCSD theory. The computed correlation energies are decomposed into singlet and triplet pair energies. It is established that the singlet pair energies converge as X^?3 and the triplet pair energies as X^?5 with the cardinal number of the correlation-consistent basis sets, and an extrapolation technique is proposed that takes into account their different convergence behaviour. Applied to the cc-pV5Z and cc-pV6Z results, this new extrapolation yields pair energies with a mean absolute deviation of 0.02 mE_h from the CCSD-R12/B reference values. For the seven systems under study, the extrapolated total valence shell correlation energies agree to within 0.2 mE_h with the CCSD-R12/B benchmark data.     

Characteristics and nature of the halogen-bonding interactions between CCl3F and ozone: a supermolecular and SAPT study

The strength and nature of the halogen-bond interactions in CCl₃F···O₃ complexes were examined by means of ab initio quantum-chemical calculations and symmetry-adapted perturbation theory (SAPT). Our calculations predict a trifurcated C–Cl···O interaction for the global minimum of CCl₃F···O₃ complex and several local minima, differing slightly in energy, separated by very low barriers. The calculations, which include a rigorous decomposition of the interaction energies, also indicate that the interaction of CCl₃F molecule with O₃ is characterised by contributions from both electrostatic and dispersion energies, with the contribution of the latter being dominant. The evaluated SAPT interaction energies for the CCl₃F···O₃ complexes are generally in good agreement with those obtained using the supermolecule CCSD(T) method, suggesting that SAPT is a proper method to study the intermolecular interactions in these complexes.     

Association energies in Re3+-doped alkaline-earth fluorides studied by computational methods

Association energies of nearest-neighbour and next-nearest-neighbour associates between substitutional, trivalent rare-earth ions and interstitial fluoride ions CaF₂, SrF₂ and BaF₂ are obtained by lattice simulation calculations. The dopant ion-fluoride ion interaction is described (i) with a set of potentials obtained with electron gas methods, and (ii) with a set of potentials derived semi-empirically from the host lattice cation-anion interaction potentials. The calculations successfully simulate the experimentally observed variations of the dopant-interstitial binding energies with the radius of the dopant ion, and with the lattice parameter of the host. The better quantitative agreement is obtained with the semi-empirical potentials. The variations are explained by an evaluation of the displacements of the ions constituting the associates.     

Nuclear modification factor for light and heavy flavors within pQCD and recent data from the LHC

The flavor dependence of the nuclear modification factor R _AA in the pQCD calculations at LHC energies has been examined. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant. Our results show that the recent LHC data on the R _AA for charged hadrons, D-mesons, and non-photonic electrons agree reasonably with the pQCD picture of the parton energy loss with the dominating contribution from the radiative mechanism.     

Study of parameters of the angular distribution of photoelectrons in the relativistic quadrupole approximation

Relativistic calculations of differential cross sections for photoionization are performed and the behavior of parameters β, γ, and δ describing the angular distribution of photoelectrons in the quadrupole approximation is studied. The calculations were carried out for a number of atoms for kinetic energies of photoelectrons E _k ≈50 000 eV. The electronic wave functions of the initial and final states are calculated by the Dirac-Fock method taking into account the exchange interaction and a hole produced in the atomic shell upon photoionization. The dependence of parameters β, γ, and δ on the physical assumptions used in the calculations is studied. Comparison with nonrelativistic calculations shows that relativistic values of the nondipole parameters γ and δ can be substantially different even at low energies of photoelectrons. Our calculations of nondipole parameters γ and δ for the 2p-shell of the Kr atom better agree with the recent experimental data than nonrelativistic calculations performed earlier taking approximately into account the exchange interaction and neglecting a hole.     

Photoelectron spectra of chromium tetranitrosyl

The ultraviolet and X-ray-excited photoelectron spectra of Cr(NO)₄ are reported. The electron binding energies, shake-up spectra, relative peak intensities and the Auger peak kinetic energies have been measured, and are compared to the spectra from gas-phase NO, from NO adsorbed on a transition metal surface, and to SCF-MS calculations. The theoretical calculations are utilized to obtain ionization energies and charge distributions, and consequently to discuss the bonding in nitrosyl complexes.     

Calculation of photoelectron spectra of the trihalides of group v elements

The SCF-Xα-SW method is applied to calculate the ionization energies of the trihalides of all of the Group V elements. The calculated orbital energies agree very well with reported experimental ionization energies. The molecular-orbital orderings obtained coincide with recent experimental orbital assignments. The results are also compared with previous ab initio, semiempirical and Xα calculations for NF₃, PF₃, PCl₃ and PBr₃. The comparison indicates that the present results show improved agreement with experiment and clarify certain ambiguities in the earlier molecular-orbital assignments.     

Small chain approximation for the electronic structure of polyacetylene

It is demonstrated that many properties of interest for polyacetylene chains can be predicted on the basis of Hartree-Fock calculations on short model molecules. The equilibrium geometries, energies per C₂H₂ unit, and isomerization energies converge by a chain length of six or eight carbons. The ionization potential, band gaps, and band widths converge more slowly, but their limiting values can be obtained readily by extrapolating results of calculations on chains up to a length of eight carbons.     

Theoretical characterization of axial deformation effects on hydrogen storage of Ti decorated armchair (5,5) SWCNT

Theoretical calculations have been performed in the framework of density functional theory to characterize the effect of axial deformation on hydrogen storage of Ti decorated armchair (5,5) SWCNT. The theoretical characterization has been carried out in terms of H₂ adsorption energies that are lying in the desirable energy window (?0.2 to ?0.6?eV) recommended by DOE, as well as a variety of physicochemical properties. A remarkable and significant change in H₂ adsorption energy is observed under the effect of only (1%) axial strain. Axial relaxation leads to H₂ adsorption energies within the recommended energy range for hydrogen storage, in contrast to axial compression. Simultaneous weakening of π and σ interactions, due to the effect of axial relaxation and loss of spatial orbital overlap, is in favor of hydrogen adsorption in the recommended energy range, and dominates the effect of charge transfer from Ti 3d to C 2p of the SWCNT. The calculated pairwise and non pairwise additive components confirm that the role of the SWCNT is not restricted to supporting the metal. Polarizability and hperpolarizabilty calculations as well as spectral analysis characterize the relaxed structure (Z?=?1.02), for which H₂ adsorption energy (?0.34?eV) is in the recommended energy range for hydrogen storage, to be energetically more preferable than the compressed structure (Z?=?0.99). The results offer a way to control and characterize the hydrogenation process of metal functionalized SWCNTs by strain loading.     

Near-barrier fusion reactions induced by α on197Au,193Ir,191Ir,185Re,181Ta,121Sb and69Ga nuclei

Fusion-evaporation cross-sections for the α-induced reactions upon¹⁹⁷Au,¹⁹³Ir,¹⁹¹Ir,¹⁸⁵Re,¹⁸¹Ta,¹²¹Sb and⁶⁹Ga nuclei at bombarding energies near the Coulomb barrier have been measured by off-line observation of the γ-rays emitted in the radioactive decay of the residual nuclei using stacked foil technique. The total fusion cross-section for the systems have been compared with simple statistical model calculations using the code ALICE/91 as well as with the coupled channel calculations that include the β₂ and ν₄ slatic deformations and dynamic couplings of the vibrational/rotational states of the target and the projet tile using the code CCDEF.     

Electron correlations in a C20 fullerene cluster

The ground-state properties of C₂₀ fullerene clusters are determined in the framework of the Hubbard model by using lattice density-functional theory (LDFT) and scaling approximations to the interaction-energy functional. Results are given for the ground-state energy, kinetic and Coulomb energies, local magnetic moments, and charge-excitation gap, as a function of the Coulomb repulsion U/t and for electron or hole doping δ close to half-band filling (|δ| ≤1). The role of electron correlations is analyzed by comparing the LDFT results with fully unrestricted Hartree-Fock (UHF) calculations which take into account possible noncollinear arrangements of the local spin-polarizations. The consequences of the spin-density-wave symmetry breaking, often found in UHF, and the implications of this study for more complex fullerene structures are discussed.     

Effect of orthorhombic distortion and electron correlation on the electronic structure of SrMnO3 from first principles

The total energies and electronic structures of SrMnO₃ are studied from first principles calculations within the generalized-gradient approximation (GGA) framework. The orthorhombic structure with AFM1 configuration (see Fig. 1) is found to be the ground state of SrMnO₃, consistent with the latest experimental observation. The orthorhombic distortion effect of SrMnO₃ is studied by comparing its electronic structure and that of cubic structure, while correlation effect is evaluated by comparing GGA and GGA+U calculations. In contrast to previous theoretical studies, our calculations show that both the orthorhombic distortion and the electron correlation play important roles in the electronic structure of SrMnO₃.     

Core photoelectron spectroscopy of some acetylenic molecules

Carbon 1s binding energies have been measured for CH₃CCH, CH₃CCCH₃, CF₃CCH and CF₃CCCF₃ and compared to a verified value for acetylene. Assignments are based on the application of a CNDO potential model with relaxation corrections which is quite successful in predicting binding energy shifts and upon qualitative considerations. Substitution of CF₃ groups shifts the acetylenic C 1s binding energy from 291.2 (HCCH) to 292.2 in CF₃CCH and 292.7 eV in CF₃CCCF₃. The unequal substitutional shifts are probably due to a saturation of substituent effect expected in competitive situations. With reservations arising from uncertainties in assignment due to lack of resolution, it appears that acetylenic C 1s binding energies decrease [to 290.7 (av.) in CH₃CCH and to 290.1 eV in CH₃CCCH₃] upon replacement of H by CH₃ groups. Although the decrease in acetylenic binding energies agrees with the chemical notion that CH₃ groups are electron donating with respect to unsaturated portions of the molecule, theoretical calculations available in the literature indicate that actual electron withdrawal or donation does not occur in these differently substituted molecules. The shifts of apparent binding energy correlate reasonably well with a ground state potential model which accounts for the effect of the charge on the adjacent atoms as well as on the photoionized atom. Even better correlation is obtained if the atomic potentials are corrected for electronic redistribution (relaxation) effects which occur during the photoionization process, and it is suggested that relaxation effects make a significant contribution to shifts of apparent binding energies. Surprisingly ground state potential and relaxation corrected potential calculations with the CNDO method suggest a large difference in C 1s binding energies of the two acetylenic carbon atoms in CH₃CCH which is not verified experimentally nor mirrored by calculations on CF₃CCH. The CH₃ binding energies are 291.8 eV in CH₃CCH and 291.3 eV in CH₃CCCH₃, both higher than values assigned to CH₄ or C₂H₆.     

Low-energy electron scattering from gaseous CS<Subscript>2</Subscript>: angular distributions and effect of exchange forces

Ab initio calculations are reported for the quantum scattering of electrons from CS₂ molecules in the gas phase and for energies which range from near threshold up to about 100 eV. Angular distributions are examined in detail and an extensive comparison is made with existing experiments and earlier calculations. The agreement found with the latter data is fairly good and results are further discussed in terms of a physical mechanism of “exchange level shifting" to explain the disappearance of a Π_u resonance suggested by earlier studies.     

An attempt on the calculation of relativistic potential energy curves: Noble gas difluorides

Total energy SCF calculations were performed for noble gas difluorides in a relativistic procedure and compared with analogous non-relativistic calculations. The discrete variational method with numerical basis functions was used. Rather smooth potential energy curves could be obtained. The theoretical Kr-F and Xe-F bond distances were calculated to be 3.5 a.u. and 3.6 a.u. which should be compared with the experimental values of 3.54 a.u. and 3.7 a.u. Although the dissociation energies are off by a factor of about five it was found that ArF₂ may be a stable molecule. Theoretical ionization energies for the outer levels reproduce the experimental values for KrF₂ and XeF₂ to within 2 eV.     

Quantum chemical modelling of “green” luminescence in ABO perovskites

The origin of the intrinsic excitonic (“green”) luminescence in ABO₃ perovskites remains a hot topic over the last quarter of a century. We suggest as a theoretical interpretation for the “green” luminescence in these crystals, the recombination of electron and hole polarons forming a charge transfer vibronic exciton. In order to check quantitatively the proposed model, we performed quantum chemical calculations using the Intermediate Neglect of Differential Overlap (INDO) method combined with the periodic defect model. The luminescence energies calculated for four perovskite crystals are found to be in good agreement with experimental data. Received 19 December 2001 and Received in final form 14 March 2002 Published online 25 June 2002     

Elastic scattering of electrons by benzene

Relative differential cross-sections for the elastic scattering of electrons from benzene have been measured at incident energies 300, 500, 700 and 900eV and for scattering angles between 30° and 120°. The results are discussed and compared with the independent atom model (IAM) calculations. Two different sets of scattering amplitudes for the constituent atoms of benzene were used in these calculations, one obtained from first Born approximation and the other from partial wave analysis of the Dirac equation. Only the static interaction was taken into account in the calculations. The higher the incident energy, the better is the observed agreement between experiment and theory. This indicates that at higher energies, absorption, exchange and polarization effects are not significant as compared to the static interaction and that the IAM satisfactorily predicts the interference of scattering from the individual atoms of C₆H₆.