H_3~+体系基态和电子激发态的价键方法研究

本文应用价键理论的键表酉群方法,讨论H_3~+体系的基态及其几个低激发态,研究了该体系处于激发态时价键结构的变化,得到H_3~+体系的基态为等边三角形,第一激发态为直线型,第二、三激发态为等腰三角形,且基本简并.     

A multi-configuration LCAO–MO study for complex unsaturated molecules. I. General theory and its application to the benzene anion

A multi-configuration LCAO –MO approach using a π-bond order–bond length linear relation is introduced to predict the geometrical structures for the electronic ground and excited states of unsaturated hydrocarbons. The procedure is designed to include configuration interaction in each iterative computation where the π-electron approximation is employed under the Pariser–Parr type semi-empirical treatment. The π-bond order–bond length relation is determined as r_pq = 1.523 – 0.193P_pq, when the bond lengths of ethylene, benzene and naphthalene are used and the groundstate functions including the singly and doubly excited configurations are taken into account to obtain the bond orders P_pq. The iterative calculation is applied to the ground state and the two lowest excited states of the benzene anion in both D_6h and D_2h molecular geometries. The geometrical structures and the π-electron energies are computed for the ground and excited states of the anion; for the latter, two types of configuration species are used. It is found that the first lowest excited state is not subjected to the Jahn–Teller effect and the calculated excited state energies do not agree with the observed values (c. 1.0 ～ 2.5 eV higher than the observed values). The latter point is discussed in detail. It is also found that the resultant ground state energy depression due to configuration mixing is not very large and the two types of configuration species used give different CI effects on the energy levels of the two lowest excited states of the anion. Finally, the stabilization energy due to the Jahn–Teller distortion is estimated for the ground state of the anion.     

A multi-configuration LCAO–MO study for complex unsaturated molecules. II. Application to the benzene cation

The method of the MC –LCAO –MO approach, described in the preceding paper, is further applied to the benzene cation. Through the iteration process the π-electron energies and the molecular shapes are computed for the ground and two lowest excited states of the cation in both D_6h and D_2h geometries. A remarkable fact obtained is that a comparatively small variation of the geometrical structure (c. 0.010 – 0.013 Å bond length difference) brings about a considerable change of the energy value (c. 0.85 – 1.25 eV). The π-electronic excitation energies obtained from the iteration process are compared with the transition energies calculated from the usual method in which the structures of the excited states are assumed to be the same as the corresponding ground state structures. The difference in the excitation energy between the cation and the anion, and the CI effect on the excited states, are discussed. It is found that the doubly excited configurations play an important role in CI , which is somewhat different from that of the singly excited configurations. The stabilization energy due to the Jahn–Teller distortion is estimated for the ground state of the cation.     

Construction and applications of symmetrized valence bond wave functions

A method constructing symmetry-adapted bonded Young tableau bases is proposed, based on the symmetry properties of bonded tableaus and the projection operator associated with a point group. Several examples including the ground states and π excited states of O₃⁻, O₃, O₃⁺, and C₃⁻ are shown for instruction to construct the symmetrized valence bond (VB) wave function. Excitation energies of transitions from the ground states to π excited states of O₃⁻, C₃H₅, and C₃⁻ are calculated with an optimized symmetrized valence bond wave function in the σ–π separation approximation. Good agreement between the VB and experimental excitation energies is observed. The bonding features of the ground state and the first π excited singlet and triplet states for S₃ are discussed according to bonding populations from VB calculations. Both the singlet-biradical and the dipole structures have significant contributions to the ground state X ¹A₁ of S₃, while the excited state 1 ¹B₂ is essentially composed of the dipole structures, and the 1 ³B₂ excited state is comprised from a triplet-biradical structure. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 1–7, 1998     

Effect of the state of h-b-1 hydrogen bond on the character of some atom vibrations in guanine-cytosine pair of the DNA molecule

For the first hydrogen bond of the guanine-cytosine (G-C) pair, the potential function V(r, R) is found for the nonequilibrium bond length R. A new form of the semiempirical potential function, Clementi's calculations for V(r, R₀) and some experimental data are used. New wave functions and energy levels as a function of the H-bond length for the ground and several excited states are obtained. This allows one to obtain frequencies and amplitudes of some vibrations of the G-C pair side groups involved in the formation of the hydrogen bond when the latter is not excited and when it is excited to the first energy level. © 1996 John Wiley & Sons, Inc.     

NH_2基态和激发态的SAC－CI和量子拓扑方法研究

ＮＨ_２基态和激发态的ＳＡＣ－ＣＩ和量子拓扑方法研究郑世钧，蔡新华，宋天乐，孟令鹏，中迁博，波田雅彦（河北师范学院化学系，石家庄，０５００９１）（京都大学工程学院京都，日本）关键词ＳＡＣ－ＣＩ方法，激发态，电子密度，拓扑分析用量子拓扑学方法研究激发态...     

A SEARCH FOR LUMINESCENT FREE RADICAL RECOMBINATION

Abstract— Radical recombinations producing a single bond are potentially chemiluminescent reactions. The probability that a radical recombination leads to an excited state will depend on the relative shape of the ground and excited surfaces. This information can be obtained from the rate constants of the ground state and excited states dissociation, and the energy differences between the states. From the available data it was concluded that acyl radicals are among the most promising radicals regarding the probability of recombination leading to excited triplet states. Experimental efforts to detect luminescence following the recombination of acyl radicals will be discussed.     

Coupled cluster investigation on the low-lying electronic states of CuCN and CuNC and the ground state barrier to isomerization

The observation of several metal cyanides and isocyanides in interstellar space has raised much interest these molecules. Optimum molecular structures, harmonic vibrational frequencies, and dipole moments of the ground electronic states (X1Sigma+), triplet excited states, and open shell singlet excited states of CuCN and CuNC were determined using different levels of nonrelativistic and scalar relativistic (Douglas-Kroll) [Ann. Phys. 82, 89 (1979)] coupled cluster theory in conjunction with atomic natural orbital basis sets and correlation consistent basis sets. For the relativistic computations the specially contracted correlation consistent Douglas-Kroll (DK) basis sets were used. Moreover, barriers to isomerization from CuCN to CuNC were computed. The predicted structures of the X1Sigma+ state for CuCN are re(Cu-C)=1.826 A and re(C-N)=1.167 A, at the most sophisticated level of theory, the scalar relativistic DK-CCSD(T)/cc-pVQZ(DK) method. These results are in excellent agreement with the experimentally determined Cu-C bond length of 1.829 A and C-N bond distance of 1.162 A. At the same level of theory, the zero-point corrected barrier to isomerization from CuCN to CuNC is estimated to be 14.7 kcal mol(-1), and the cyanide is more stable than the isocyanide by 11.5 kcal mol(-1). For both CuCN and CuNC the 3Sigma+ state is the lowest lying excited electronic state. At the DK-CCSD/cc-pVQZ(DK) level of theory, the energetic ordering of excited states of CuCN and CuNC is X1Sigma+相似文献   

Deflation techniques in quantum chemistry: Excited states from ground states

Applications of deflation techniques to the study of excited states of quantum systems are analyzed. It is demonstrated how these methods allow us to transform the excited state problem of one Hamiltonian, into the ground state problem of an auxiliary one. As an example, potential application in the density functional treatment of excited states is discussed. The inclusion of approximations in this scheme, such as the solution of the proposed model within a finite basis set is discussed. An extension of the Hartree–Fock (HF) method to excited states is presented. This new treatment includes previous self consistent field extensions to excited states and provides us with a way to obtain the HF extension to excited states of any ground state method. These results make the excited states of a system accessible through all ground state theoretical techniques. © 2013 Wiley Periodicals, Inc.     

Die optische Aktivität von chiralen Dienen,Enonen und α-Diketonen

The ground state and excited states of butadiene, acrolein and glyoxal are calculated by the SCF-CNDO-CI method. The gauche conformers of these molecules, obtained by a twist about the formal C? C single bond, have served as models for the study of the optical activity of dienes, α,β-unsaturated ketones and α- and β-diketones. An analysis of the molecular orbitals of the ground state and of excited states leads to the conclusion that the sign of a Cotton effect is determined primarly by the nodal properties and the helicity of the ground and excited state orbitals [20]. In cyclopentenones the longest wavelength Cotton effect does not obey the rule deduced from the twisted acrolein model. This apparent anomaly is explained on the basis of the altered nodal properties of cyclopentenones as compared to cyclohexenones. Concerning diones, the comparison of experimental CD. and UV. spectra with the calculated data allows the assignment of the five lowest Cotton effects of camphor quinone. It is found that α-diketones have only two singletsinglet transitions in the region from 500 nm to 250 nm. In contrast, the next strong UV. absorption between 220 nm and 190 nm consists of three distinct electronic transitions, the nature of which is discussed. These findings are correlated with the previously calculated [8] symmetry properties and ordering of the energy levels of the ground state and excited states of planar trans and cis glyoxal. From these results the most likely conformations of a number of α-diketons are derived.     

Iterative Cl general singles and doubles (ICIGSD) method for calculating the exact wave functions of the ground and excited states of molecules

The iterative configuration-interaction general singles and doubles (ICIGSD) method was applied to various closed- and open-shell electronic states of molecules within finite basis sets and was shown to give the exact results that are identical to the full CI ones. The structure of the ICIGSD is unique among the ICI formalisms, that is, the singularity problem intrinsic to atomic and molecular Hamiltonians can be avoided. The convergence of the ICIGSD method was fairly good regardless of the characters of the electronic states and the qualities of the basis sets; only several iterations were enough for obtaining microhartree accuracy. These favorable properties are attributed to the unique GSD structure. The present method was shown to be applicable to various spin states and to quasidegenerate states appearing in bond dissociation process. We have also applied the ICIGSD-CI method to calculate the excited states simultaneously. We have confirmed that the ICIGSD-CI method is accurate for calculating the excited states the symmetries of which are not only similar to but also different from that of the ground state.     

The calculation of ground and excited doublet state molecular polarizabilities by the CNDO/S-CI method

The calculation of ground and excited state molecular polarizabilities by the CNDO/S-CI method has been extended to include doublet states. As incorporated, the second order perturbation scheme usually predicts average state polarizabilities of molecular cation ground states to be lower than the corresponding singlet ground states. Average anion polarizabilities are generally found to be higher than those of the corresponding singlet states. Excited doublet state polarizabilities are presented for the molecular cation of formaldehyde, benzene, 1,3,5-trans-hexatriene, and naphthalene. Due to the unavailability of experimental data it is currently impossible to assess appropriately the quality of these results.     

Multiconfiguration Pair-Density Functional Theory for Transition Metal Silicide Bond Dissociation Energies,Bond Lengths,and State Orderings

Transition metal silicides are promising materials for improved electronic devices, and this motivates achieving a better understanding of transition metal bonds to silicon. Here we model the ground and excited state bond dissociations of VSi, NbSi, and TaSi using a complete active space (CAS) wave function and a separated-pair (SP) wave function combined with two post-self-consistent field techniques: complete active space with perturbation theory at second order and multiconfiguration pair-density functional theory. The SP approximation is a multiconfiguration self-consistent field method with a selection of configurations based on generalized valence bond theory without the perfect pairing approximation. For both CAS and SP, the active-space composition corresponds to the nominal correlated-participating-orbital scheme. The ground state and low-lying excited states are explored to predict the state ordering for each molecule, and potential energy curves are calculated for the ground state to compare to experiment. The experimental bond dissociation energies of the three diatomic molecules are predicted with eight on-top pair-density functionals with a typical error of 0.2 eV for a CAS wave function and a typical error of 0.3 eV for the SP approximation. We also provide a survey of the accuracy achieved by the SP and extended separated-pair approximations for a broader set of 25 transition metal–ligand bond dissociation energies.     

The lowest electronic states of the benzoyl ion. A molecular orbital study with configuration interaction

A configuration interaction method of molecular orbital theory shown to be accurate for the calculation of excited state energies in several aromatic systems was applied to the problem of excited states of the benzoyl ion. The excited singlet and triplet states of the benzoyl ion lie at least 3.8 eV and 2.6 eV, respectively, above the ground state. These results are not in agreement with a postulated state 20 kcal above the ground state. On the other hand, the charge distribution in excited states does agree with that postulated for the 20 kcal state. The p-hydroxy and p-cyano substituents do not greatly influence the charge distribution between the ring and the carbonyl group in either the ground or lowest excited states.     

Absorption spectra of ground-state and low-lying electronic States of copper nitrosyl: a rare gas matrix isolation study

The reaction of ground-state Cu atoms with NO during condensation in solid argon, neon, and binary argon/neon mixtures has been reinvestigated. In addition to the ground-state already characterized in rare gas matrixes by its nu1 mode in reactions of laser-ablated Cu with nitric oxide, another very low lying electronic state is observed for CuNO in solid argon. Photoconversion and equilibrium processes are observed between the two lowest lying electronic states following photoexcitations to second and third excited states in the visible and near-infrared. The electronic spectrum of the CuNO complex was also recorded to understand the photoconversion processes. In solid neon, only the ground state (probably 1A') and the second and third excited states are observed. This suggests that interaction with the argon cage stabilizes the triplet state to make 1A' and 3A' ' states almost isoenergetic in solid argon. On the basis of previous predictions founded on DFT calculations on the very low lying 1A' and 3A' ', a mechanism is proposed, involving the singlet-triplet state manifolds. For these two lower and one higher electronic states, 14N/15N, 16O/18O, and 63Cu/65Cu isotopic data on nu1, nu2, and nu3 have been measured. On the basis of harmonic force-field calculations and relative intensities in the vibronic progressions, some structural parameters are estimated. The molecule is bent in all electronic states, with Cu-N-O bond angles varying slightly around 130 +/- 10 degrees , but the Cu-N bond force constants are substantially different, denoting larger differences in bond lengths.     

Electronic structure of benzaldehyde: A comparative study of the lowest excited singlet π* ← π and π* ← n states

VE-PPP, CNDO/2, and CNDO/s-CI methods have been used to investigate the electronic spectrum and structure of benzaldehyde. Electronic charge distributions and bond orders in the ground and lowest excited singlet π* ← π and π* ← n states of the molecule have been studied. The molecule has been shown to be nonplanar in the lowest π* ← n excited singlet state, in agreement with the conclusions drawn from the study of vibrational spectra. Dipole moments in both excited states have been shown to be larger than the ground-state value. Thus, the ambiguity in the experimental result for the π* ← π n excited singlet state dipole moment has been resolved. It has been shown that the n orbital is mainly localized on the CHO group. Furthermore, charge distributions, dipole moments, and molecular geometries are shown to be very different in the excited singlet π* ← π and π* ← n states.     

SCF MO CI perturbation calculations of inner shell and valence shell vertical ionization potentials

A CI method for calculating inner and valence shell vertical ionization potentials is presented. It is based on ab initio SCF MO calculations for the neutral closedshell ground state followed by CI perturbation calculations for the ground and ion states including all spin and symmetry adapted singly and doubly excited configurations with respect to the main configurations of the state of interest. The state energy is computed by performing a CI calculation for a set of selected configurations, and then adding the contributions of the remaining configurations as estimated by second order Brillouin-Wigner perturbation theory. The use of the same set of MO's for all states together with the CI perturbation method makes the method rather rapid. The numerical results are, in spite of the limited Gaussian basis sets used, in good agreement with experiment.     

Real space Hartree-Fock configuration interaction method for complex lateral quantum dot molecules

We present unrestricted Hartree-Fock method coupled with configuration interaction (CI) method (URHF-CI) suitable for the calculation of ground and excited states of large number of electrons localized by complex gate potentials in quasi-two-dimensional quantum dot molecules. The method employs real space finite difference method, incorporating strong magnetic field, for calculating single particle states. The Hartree-Fock method is employed for the calculation of direct and exchange interaction contributions to the ground state energy. The effects of correlations are included in energies and directly in the many-particle wave functions via CI method using a limited set of excitations above the Fermi level. The URHF-CI method and its performance are illustrated on the example of ten electrons confined in a two-dimensional quantum dot molecule.