Single Excitation Configuration Research Articles

1,2-, 1,3-dioxetanes, 그리고 1,3-cyclodisiloxane의 분자구조, 에너지와 진동주파수에 대한 순 이론 양자 역학적 연구

1,2-와 1,3-dioxetane<TEX>$(C_2O_2H_4)$</TEX>, 그리고 1,3-cyclodisiloxane<TEX>$(Si_2O_2H_4)$</TEX>에 대하여 높은 이론 수준에서 분자구조, 진동주파수, 그리고 에너지 등을 계산하였다. 위의 모든 분자들에 대하여 TZ2P CCSD(T)의 이론 수준까지 분자구조를 최적화 하였으며. 진동주파수는 여러 basis set에서 SCF 방법으로 계산하였다. 본 연구에서 최적화된 분자구조들에 대한 진동주파수가 모두 실수(real number)로 예측됨으로서, 제안된 모든 분자구조가 local minimum 구조임을 확인하였다. 1,2- 및 1,3-dioxetane들과 cyclodisiloxane이 두 분자의 aldehyde와 silanone으로 해리 될 때의 중합에너지를 zero-point vibrational energy(ZPVE)를 고려하여 계산하고, 안정성을 비교하였다. The geometrical parameters, vibrational frequencies, and relative energies for 1,2-, 1,3-dioxetanes, and 1,3-cyclodisiloxane have been investigated using high level ab initio quantum mechanical techniques with large basis sets. The geometries have been optimized at the self-consistent field(SCF), the single and double excitation configuration interaction(CISD), the coupled cluster with single and double excitation(CCSD), and the CCSD with connected triple excitations[CCSD(T)] levels of theory. The highest level of theory employed in this study is TZ2P CCSD(T). Harmonic vibrational frequencies and IR intensities are also determined at the SCF level of theory with various basis sets and confirm that all the optimized geometries are true minima. Also zero-point vibrational energies have been considered to predict the dimerization energies for 1,2- and 1,3-isomers.

A theoretical study on lower electronic states of CoN

In order to identify the ground state of CoN, we carried out calculations of multi-reference single and double excitation configuration interaction with Davidson-type correction and multi-reference coupled pair approximation (MRCPA). MRCPA predicts that 1Σ + is the ground state of CoN. The 5 Δ state lies only 0.223 eV above 1Σ +. Internuclear equilibrium distance, harmonic frequency, and rotational constants of 1Σ + agree well with experimental results.

Time-Dependent Density Functional Study of Electroluminescent Polymers

The theoretical spectra of electroluminescent polymers are studied with time-dependent density functional theories, followed by a systematic scheme with a symmetry restriction to extrapolate the absorption and emission corresponding to infinite chains avoiding periodic boundary conditions. Application to poly(p-phenylene vinylene) (PPV) and the derivatives has been attempted, and the hybrid B3LYP is concluded to be the most suitable functional for computation. The theoretical excitation energies of PPV by B3LYP/6-31G*//B3LYP/STO-3G and B3LYP/6-311G* are 2.107 and 2.027 eV, respectively. With optimization performed by single-excited configuration interaction, the emission spectroscopy can be estimated. By our scheme, the Stokes shift of PPV is calculated to be 0.223 eV, which corresponds to approximately 62 nm in the spectral region.

First principles prediction of isotopic shifts in H2O

We compute isotope-independent first- and second-order corrections to the Born–Oppenheimer approximation for water and use them to predict isotopic shifts. For the diagonal correction, we use internally contracted multireference configuration interaction wave functions and derivatives with respect to mass-dependent internal coordinates to generate the mass-independent correction functions. For the nonadiabatic correction, we use a self-consistent field wave function for the ground electronic state and single excitation configuration interaction wave functions for the excited states and a generalization of the Handy, Yamaguchi, and Schaefer method to obtain mass-independent correction functions. We find that including the nonadiabatic correction gives significantly improved results compared to just including the diagonal correction when the Born–Oppenheimer potential energy surface is optimized for H2 O16. The agreement with experimental results for deuterium- and tritium-containing isotopes is nearly as good as our best empirical correction, however, the present correction is expected to be more reliable for higher, uncharacterized, levels.

The singlet electronic excited states of the F2 molecule

By using multireference single excitation configuration interaction calculations and multireference single and double excitation CI calculations, we consider the Σu+1, Πg1, and Πu1 excited states of the F2 molecule which lie between 4.3 and 14.1 eV above the ground state. The basis set is composed of 13s, 10p, 7d, and 2 f contracted Gaussian-type functions, and covers molecular orbitals spanned by 4s, 4p, and 3d Rydberg orbitals. Of the Σu+1 states, G 1Σu+ is sometimes disregarded, presumably because it is not directly observed by optical measurements, but is inferred from perturbations in the visible and ultraviolet spectra. We find that G 1Σu+ arises from the shallow local minimum in the lowest Σu+1 potential curve, which also has a stable minimum corresponding to the state designated C 1Σu+. The experimental excitation energies (T0 values) for G 1Σu+ are 12.81–12.87 eV according to electron energy loss spectroscopy, and our theoretical value is 13.06 eV. Agreement between the experiment and the calculation is quite close. The state has a mixed ionic-Rydberg character with an interesting Rydberg portion. The experimental and calculated T0 values for C 1Σu+ are, respectively, 11.57 and 11.59 eV, suggesting that the present calculation for the state is reliable. Ambiguity found in experimental assignments of the vibrational levels for C 1Σu+ is settled here. The Πg1 and Πu1 states are also discussed.

Theoretical study on lower electronic states of the FeSi molecule

The low lying electronic states of the FeSi molecule have been investigated by performing complete active space self-consistent field (CASSCF) and multireference single and double excitation configuration interaction (MRSDCI) calculations. Although the classification of the ground state was not established, the results of the MRSDCI calculations suggest that the ground state of FeSi is 3Δ, and the lowest excited state is 5Π whose transition energy is 0.36 eV including the Davidson-type Q correction. The R e given by MRSDCI with Q correction is 2.23 Å for 3Δ and 2.19 Å for 5Π. The spectroscopic constants and dipole moments of the low lying 5Δ and 3Π states as well as the 3Δ and 5Π states are also evaluated. The bonding nature of FeSi in the 3Δ state is discussed in comparison with the FeC molecule.

Electronic Excitations in Pyrrole: A Test Case for Determination of Chromophores in the Chromogenic Effects of Neurotoxic Hydrocarbons by Time-Dependent Density Functional Theory and Single-Excitation Configuration Interaction Methods

Time-dependent density functional theory (TD-DFT) and single-excitation configuration interaction (CIS) calculations on the electronic excitations in pyrrole have been performed to examine the reliability of these first-principles electronic structure methods in predicting electronic excitation spectraof pyrrole-containing compounds. Both the TD-DFT and CIS calculations led to satisfactory results when compared to available experimental data, particularly for low-lying excited states. The TD-DFT and CIS calculations provide lower and upper limits of the excitation energies, respectively, for low-lying singlet excited states. These results suggest that these methods can be used for the prediction of the excitation spectra, particularly the excitation energies for low-lying excited states, of chromophores responsible for the chromogenic effects of neurotoxic hydrocarbons, which are believed to be substituted pyrroles and their adducts with proteins. As an example of a practical application, the spectrum of the widely used 2,5-dimethylpyrrole has been calculated. It is shown that the 2,5-dimethylpyrrole molecule does not have an absorption in the region of the visible spectrum (400–700 nm), suggesting that the absorption observed at 530 nm and the color of 2,5-dimethylpyrrole is due to another species, probably a product of possible 2,5-dimethylpyrrole autoxidation. This suggests that the conclusions from previously reported experimental studies of biochemical reactions of neurotoxic γ-diketones need to be reexamined in terms of the relationship of chromogenicity to neurotoxicity.

Hydrogen transfer in photoexcited phenol/ammonia clusters by UV–IR–UV ion dip spectroscopy and ab initio molecular orbital calculations. I. Electronic transitions

The electronic spectra of reaction products via photoexcited phenol/ammonia clusters (1:2–5) have been measured by UV-near-IR–UV ion dip spectroscopy. Compared with the electronic spectra of hydrogenated ammonia cluster radicals the reaction products have been proven to be (NH3)n−1NH4 (n=2–5), which are generated by excited-state hydrogen transfer in PhOH–(NH3)n. By comparing the experimental results with ab initio molecular orbital calculations at multireference single and double excitation configuration interaction level, it has been found that the reaction products (NH3)n−1NH4 (for n=3 and 4), contain some isomers.

An ab initio study of ion-pair formation from the third [formula omitted] state of ArHCl

Photoexcited molecules in the vacuum ultraviolet region electronically relax via Rydberg and intra-valence excited states. As an example of such relaxation processes, ion-pair formation of ArHCl+ hν→ArH ++Cl − from the third 1 A ′ electronic state of ArHCl is studied theoretically. The potential energy surfaces are calculated at the level of multi-reference single and double excitation configuration interaction theory. Detailed energetics of the ion-pair formation is discussed. It is found that the present molecular system has a potentiality to enhance the ion-pair formation owing to the large electronic polarizability and high ionization threshold of Ar.

A Comparative ab Initio Multireference Single and Double Excitation Configuration Interaction Study of the Electronic Spectra of Low-Lying Linear and Cyclic C5H Isomers

Multireference configuration interaction (MRD-CI) calculations are performed to compute the electronic spectra of the three low-lying isomers of C5H, a molecule of radio-astronomical interest. The electronic spectrum of linear C5H is dominated by two transitions computed at 4.13 eV (2Π ← X2Π) and 6.11 eV (2Π ← X2Π). Τhe first dipole-allowed transition is calculated at 2.54 eV (2Δ ← X2Π). Further relatively strong excitations are obtained at 2.71 eV (2Σ- ← X2Π) and 4.00 eV (2Π ← X2Π). The first dipole-allowed excitation of a C2v symmetric ring-chain isomer is calculated at 1.27 eV (2A1 ← X2B2). Up to 3.61 eV (2A2 ← X2B2), no other dipole-allowed transitions are obtained, whereas the spectrum of a Cs symmetric ring-chain structure shows several dipole-allowed excitations in the energy interval between 0.85 and 2.53 eV, including a dominating transition computed at 1.67 eV (2A‘ ← X2A‘).

The concerted mechanism of photo-induced biprotonic transfer in 7-azaindole dimers: structure, quantum-theoretical analysis, and simultaneity principles.

Six stable dimer models for 7-azaindole (including the classic C(2h) doubly hydrogen-bonded, coplanar, centrosymmetric dimer) are considered to be observable in adiabatic nozzle jet molecular beams. They are analyzed by hybrid density functional theory (DFT), the MP2 ab initio method for the ground electronic state, and the single-excitation configuration interaction (CIS) (over frozen ground state optimized geometries obtained from DFT) excited state calculations, for global potential minima and proton-transfer potential energy curves. Three simultaneity principles are stated: (i) intermolecular coherent excitation molecular exciton simultaneity, (ii) intramolecular acid-base change simultaneity at the pyrrolo-N-H and aza-N proton-donor, proton-acceptor sites, and (iii) intermolecular simultaneity of catalytic proton-donor, proton-acceptor action. It is suggested that the formation of the classic C(2h) dimer of 7-azaindole, which is considered exclusively by previous researchers, can be formed from at least one of the several card-pack hydrogen-bonded dimers in a secondary slower step approaching a microsecond scale, instead of the picosecond events at the supersonic nozzle. It is proposed that the complexity of dimerization modes is the basis of the postexcitation, postionization diverse kinetic isotope results.

Theoretical study of interactions between the Si [formula omitted] surface and metal atoms

We investigated the interactions between the Si(1 1 1) surface and the Na and Mg atoms using cluster model calculations. Calculations were performed at levels of the complete-active-space self-consistent-field and multi-reference single and double excited configuration interaction calculations using the model core potential method. Our calculations revealed that the most favorable sites of Na and Mg adsorption on Si(1 1 1) are on-top (T 1) and bridge (B 2) sites, respectively. The nature of chemical bonds between these metal atoms and the dangling bonds of the surface Si atoms are found to be essentially covalent.

Relativistic effects on magnetic circular dichroism studied by GUHF/SECI method

Quasi-relativistic formulation of the Magnetic circular dichroism (MCD) Faraday terms are presented using the generalized unrestricted Hartree–Fock (GUHF)/single excitation configuration interaction (SECI) method combined with the finite perturbation method and applied to the MCD of the three n–σ ∗ states ( 3 Q 1, 3 Q 0, 1 Q 1) of CH 3I. The Faraday B term for the 1 Q 1 state was 0.1976( Debye) 2( Bohr magneton )/(10 3 cm −1) in the non-relativistic theory, but was dramatically improved by the relativistic effect and became 0.0184 in agreement with the experimental values, 0.014 and 0.0257. This change was mainly due to the one-electron spin–orbit (SO1) term rather than the spin-free relativistic (SFR) and the two-electron spin–orbit (SO2) terms.

The Schwinger multichannel method (SMC) calculations for Zeff were off by a factor of Z

Our previously reported Z eff values were in accidental agreement with experiment. They were actually underestimated by a factor of Z. In order to full understand the nature of the discrepancies with experimental data, we carried out several tests for positron–He collisions. We first tried many different (Cartesian Gaussian) basis sets in a single-excitation configuration–interaction (CI) framework. Then, we included single- and double-excitations of the target in the CI expansion (CISD) of the scattering wave function. Finally, we tried to mimic the virtual positronium cusp. It seems that cusp description should indeed be further improved.

A theoretical study on the ionization of NO2 with analysis of vibrational structure of the photoelectron spectrum

Ab initio calculations have been performed to study the molecular structures and the vibrational levels of the low-lying ionic states (1A1, B23, A23, A21, B21, B11, 2 1A1, B13, and A13) of nitrogen dioxide. The global regions of the potential energy surfaces have been obtained by multireference single and double excitation configuration interaction calculations. Vibrational calculations using vibrational Hamiltonians have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of these states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states are also presented and are compared with the photoelectron spectra. A new assignment of the photoelectron spectra has been proposed.

Linear and Nonlinear Polarizabilities of Fragmental Molecules for the Phenylacetylene Dendrimers

Abstract Linear and nonlinear polarizabilities of small fragmental molecules for the phenylacetylene dendrimers have been calculated with the frequency-dependent moment schemes based on the sum-over-states expressions of the polarizabilities, including all of the singly-excited configurations in the semiempirical CNDO/S approximation. The smallest system, consisting of two benzene rings connected by an acetylene chain, corresponds to a molecular unit that is usually adopted in the exciton model for a theoretical analysis of the phenylacetylene dendrimers. The dependences of the polarizabilities upon the molecular size were examined. It has been shown that the linear polarizability in the static-field condition increases linearly with the number of acetylene chains (N). MO calculations of the nonlinear polarizabilities of these molecules have been carried out for the first time. The third-order polarizability in the static-field condition is shown to depend quadratically upon N, which suggests that two chromophores at a time participate in the optical process of the third-order polarization.

The first enantiomerically pure [n]triangulanes and analogues: sigma-[n]helicenes with remarkable features.

(M)-(-)- and (P)-(+)-Trispiro[2.0.0.2.1.1]nonanes [(M)- and (P)-3] as well as (M)-(-)- and (P)-(+)-tetraspiro[2.0.0.0.2.1.1.1]undecanes [(M)- and (P)-4]-enantiomerically pure unbranched [4]- and [5]triangulanes-have been prepared starting from racemic bicyclopropylidenecarboxylic [(1RS)-12] and exo-dispiro[2.0.2.1]heptane-1-carboxylic [(1RS,3SR)-13] acids. The optical resolutions of rac-12 and rac-13 furnished enantiomerically pure acids (S)-(+)-12, (R)-(-)-12, (1R,3S)-(-)-13, and (1S,3R)-(+)-13. The ethyl ester (R)-25 of the acid (R)-(-)-12 was cyclopropanated to give carboxylates (1R,3R)-26 and (1R,3S)-26. The ester (1R,3S)-26 and acids (1R,3S)-13 and (1S,3R)-13 were converted into enantiomerically pure methylene[3]triangulanes (S)-(-)- and (R)-(+)-28. An alternative approach consisted of an enzymatic deracemization of endo-[(1SR,3SR)-dispiro[2.0.2.1]heptyl]methanol (rac-20) or anti-[(1SR,3RS)-4-methylenespiropentyl]methanol (rac-18). This afforded (S)-(-)- and (R)-(+)-28 (starting from rac-20), as well as enantiomerically pure (M)-(-)- and (P)-(+)-1,4-dimethylenespiropentanes [(M)- and (P)-23] starting from rac-18. The methylenetriangulanes (S)-(-)- and (R)-(+)-28 were cyclopropanated furnishing (M)- and (P)-3. The rhodium-catalyzed cycloaddition of ethyl diazoacetate onto (S)-(-)- and (R)-(+)-28 yielded four diastereomeric ethyl trispiro[2.0.0.2.1.1]nonane-1-carboxylates in approximately equal proportions. The enantiomerically pure esters (1R,3S,4S)- and (1S,3R,4R)-30 were isolated by careful distillation and then transformed into [5]triangulanes (M)- and (P)-4 using the same sequence of reactions as applied for (M)- and (P)-3. The structures of the key intermediates (R)-12 and rac-31 were confirmed by X-ray analyses. Although [4]- and [5]triangulanes have no chromophore which would lead to any significant absorption above 200 nm, they have remarkably high specific rotations even at 589 nm with [alpha](20)D=-192.7 [(M)-3, c=1.18, CHCl(3))] or +373.0 [(P)-4, c=1.18, CHCl(3))]. This remarkable optical rotatation is in line with their helical arrangement of sigma bonds, as confirmed by a full valence space single excitation configuration interaction treatment (SCI) in conjunction with DFT computations at the B3LYP/TZVP//B3LYP/6-31+G(d,p) level of theory which reproduce the ORD very well. Thus, it is appropriate to call the helically shaped unbranched [n]triangulanes the "sigma-[n]helicenes", representing the sigma-bond analogues of the aromatic [n]helicenes.

A theoretical study on the ionization of OCS with an analysis of vibrational structures of the photoelectron spectrum

Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying ionic states (1, 22Π, and 1, 22Σ+) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states are also presented and are compared with the photoelectron spectrum.

Aurophilic attraction and luminescence of binuclear gold(I) complexes with bridging phosphine ligands: ab initio study.

Electronic structure and spectroscopic properties of [Au2(dpm)2]2+ (dpm = bis(diphosphino)methane) were studied by ab initio calculations. The absorption and emission spectra of this binuclear gold(I) complex in acetonitrile and in the solid state were calculated by single excitation configuration interaction (CIS) method. In the calculations, the solvent effect was taken into account by the weakly solvated [Au2(dpm)2]2+ x (MeCN)2 complex. The ground state structures of [Au2(dpm)2]2+ and [Au2(dpm)2]2+ x (MeCN)2 were optimized by the second-order Møller-Plesset perturbation (MP2) method, while the emissive triplet excited state structures were optimized by the CIS calculations. The results reveal that coordination of acetonitrile to the gold atom in the 3[d(sigma*)s(sigma)] excited state causes a significant red shift in emission energy. The weak aurophilic attraction exists in the ground states of [Au2(dpm)2]2+ and [Au2(dpm)2]2+ x (MeCN)2, and is greatly enhanced in their 3[d(sigma*)s(sigma)] excited states. In acetonitrile, the 3Au(s(sigma)) --> 1Ag(d(sigma*)) transition (phosphorescence) of [Au2(dpm)2]2+ was calculated at 557 nm, in consistent with the observed emission of [Au2(dppm)2](ClO4)2 (dppm = bis(diphenylphosphino)methane) at 575 nm. A high energy emission at 331 nm is predicted for [Au2(dpm)2]2+ in the absence of the interaction between the gold atom and solvent molecule and/or neighboring anion in the excited state. The CIS calculations on the excited states also reveal that the two absorption bands at 278 and 218 nm recorded for [Au2(dcpm)2](ClO4)2 in acetonitrile can be attributed to the 1Ag(d(sigma*)) --> 1Au(p(sigma)) and 1Ag(d(sigma*)) --> 1Au((sp)sigma) transitions, respectively.

The MRSDCI/CIS study of excited electronic states of the SF 2 radical

The vertical ( T v) and adiabatic ( T 0) excitation energies for singlet electronic excited states of the SF 2 radical have been calculated by using the multireference single and double excitation configuration interaction (MRSDCI) method and aug-cc-pVTZ basis sets augmented by Rydberg functions. The MRSDCI T v calculations indicate that the X 1 A 1 , 1 1 A 2 , 1 1 B 1 , 2 1 B 1 , 2 1 A 2 , 2 1 A 1 , 3 1 B 1 , 4 1 B 1 , 3 1 A 1 , and 1 1 B 2 states are the 10 lowest-lying singlet states. Based on the MRSDCI//CIS T 0 calculations (using CIS optimized geometries for excited states), the A, B, C, E, F, G, H, and I states of SF 2 are assigned to 1 1 B 1 , 2 1 B 1 , 3 1 B 1 , 2 1 A 2 , 2 1 A 1 , 3 1 A 1 , 4 1 B 1 , and 1 1 B 2 , respectively.