Configuration Interaction With Single Excitations Research Articles

Effect of spin–orbit coupling on strong field ionization simulated with time-dependent configuration interaction

Time-dependent configuration interaction with a complex absorbing potential has been used to simulate strong field ionization by intense laser fields. Because spin-orbit coupling changes the energies of the ground and excited states, it can affect the strong field ionization rate for molecules containing heavy atoms. Configuration interaction with single excitations (CIS) has been employed for strong field ionization of closed shell systems. Single and double excitation configuration interaction with ionization (CISD-IP) has been used to treat ionization of degenerate states of cations on an equal footing. The CISD-IP wavefunction consists of ionizing single (one hole) and double (two hole/one particle) excitations from the neutral atom. Spin-orbit coupling has been implemented using an effective one electron spin-orbit coupling operator. The effective nuclear charge in the spin-orbit coupling operator has been optimized for Ar+, Kr+, Xe+, HX+ (X = Cl, Br, and I). Spin-orbit effects on angular dependence of the strong field ionization have been studied for HX and HX+. The effects of spin-orbit coupling are largest for ionization from the π orbitals of HX+. In a static field, oscillations are seen between the 2Π3/2 and 2Π1/2 states of HX+. For ionization of HX+ by a two cycle circularly polarized pulse, a single peak is seen when the maximum in the carrier envelope is perpendicular to the molecular axis and two peaks are seen when it is parallel to the axis. This is the result of the greater ionization rate for the π orbitals than for the σ orbitals.

An efficient implementation of semiempirical quantum-chemical orthogonalization-corrected methods for excited-state dynamics.

We present an efficient implementation of configuration interaction with single excitations (CIS) for semiempirical orthogonalization-corrected OMx methods and standard modified neglect of diatomic overlap (MNDO)-type methods for the computation of vertical excitation energies as well as analytical gradients and nonadiabatic couplings. This CIS implementation is combined with Tully's fewest switches algorithm to enable surface hopping simulations of excited-state nonadiabatic dynamics. We introduce an accurate and efficient expression for the semiempirical evaluation of nonadiabatic couplings, which offers a significant speedup for medium-size molecules and is suitable for use in long nonadiabatic dynamics runs. As a pilot application, the semiempirical CIS implementation is employed to investigate ultrafast energy transfer processes in a phenylene ethynylene dendrimer model.

Photodissociation of FONO: an excited state nonadiabatic dynamics study.

The photo dissociation of nitrosyl fluorite, FONO, a potential source of atmospheric fluorine, underlies its active role in ozone depletion and other activities in the troposphere. In the present work, the electronic structure of FONO is revisited at high level of ab initio and density functional theory (DFT) theoretical levels. Several different post SCF methods were used to compute excited states, vertical excitation energies and intensities, namely configuration interaction with single excitations (CIS), equation of motion coupled cluster with single and double excitations (EOM-CCSD), and symmetry adopted cluster configuration interaction (SAC-CI) methods. The potential energy functions along two internal coordinates, namely the F-ONO bond and the FONO dihedral angle, have been computed on the ground state relaxed potential energy surface (PES) for the ground, 5A' and 5A″ excited states using the EOM-CCSD method. In the gas phase, the decay of the excited states of FONO was examined closely by calculating the UV photoabsorption cross-section spectrum and by nonadiabatic dynamics simulations. Nonadiabatic dynamics were simulated by sampling 300 trajectories in two spectral windows at 3.0 ± 0.25 and 4.5 ± 0.25eV using the surface hopping method. Two different photodissociation reaction pathways with two main products, including multifragmentation (FO+NO) and atomic elimination (F) mechanisms were identified. For the cis-isomer, the main photochemical channel is F+NO2, representing 67% of all processes. For the trans-isomer, however, the main dissociation pathway is (FO+NO). Graphical Abstract Photodisscociation of nitrosyl fluorite (FONO) seems to underlie its active role in ozone depletion and other activities in the troposphere. The present research revisits the electronic structure of FONO at high level of ab initio and DFT theoretical levels. Cis-trans isomerization and dissociation in the ground and low lying excited states were examined. Photoabsorption cross-section spectra were computed and nonadiabatic dynamics were launched for both cis and trans FONO isomers.

PH dependent photophysical studies of new europium and terbium complexes of tripodal ligand: Experimental and semiempirical approach

The photophysical properties of adduct of a novel nonadentate tripodal ligand, 5,5′-(2-(((8-hydroxyquinolin-5-yl)methylamino)methyl)-2-methylpropane-1,3-diyl)bis(azanediyl)bis(methylene diquinolin-8-ol, (TAME5OX), with Eu3+ and Tb3+ metal ions have been probed for photonics applications. The absorption spectroscopy of these complexes show remarkable spectral changes due to characteristic lanthanide transitions, which support the use of TAME5OX as a sensitive optical pH based sensor to detect Ln3+ metal ions in biological systems. In addition, these complexes have also been shown to exhibit strong green fluorescence allowing simultaneous sensing within the visible region under physiological pH in competitive medium for both Eu3+ and Tb3+ ions. The intense fluorescence from these compounds were revealed to intermittently get quenched under acidic as well as basic conditions due to the photoinduced intramolecular electron transfer from excited 8-hydroxyquinoline (8-HQ) moiety to metal ion, just an opposite process. This renders these compounds the OFF–ON–OFF type of pH-dependent fluorescent sensor. The thermodynamic stability and aqueous coordination chemistry of the chelator with the said lanthanide ions have also been probed by potentiometric, UV–visible and fluorescence spectrophotometric method. TAME5OX has been found to form two protonated complexes [Ln(H5L)]5+ and [Ln(H4L)]4+ below pH 2.5 with both metal ions, which consecutively deprotonates through one proton process with rise of pH. The formation constants (logβ11n) of neutral complexes have been determined to be 33.51 and 32.16 with pLn (pLn=−log[Ln3+]) values of 16.14 and 19.48 for Eu3+ and Tb3+ ions, respectively, calculated at pH 7.4, indicating TAME5OX is a good lanthanide synthetic chelator. The emission lifetimes of the Eu3+ and Tb3+ complexes recorded in D2O and H2O suggest the presence of water molecules in the first coordination sphere of the metal ions. NMR titrations were carried out to determine the stoichiometry of chelates. The complexe's coordination geometries were optimized by using PM7 as sparkle/PM7 model. The theoretical electronic behavior was evaluated to support the experimental findings, based on ZINDO/S methodology at configuration interaction with single excitations (CIS) level. These results emphasize the capability of the use of the theoretical models in prediction of geometries and all other calculations of compounds containing lanthanide ions and create new interesting possibilities for the design in-silico of novel and highly efficient lanthanide–organic edifice.

The influence of europium(III) and terbium(III) on the electronic system of impudent tripodal ligand: Binding, spectrophotometric and theoretical investigations

Abstract The aqueous coordination chemistry of a novel hexadentate tripodal ligand, 5-[[3-[(8-hydroxy-5-quinolyl)methoxy]-2-[(8-hydroxy-5-quinolyl)methoxymethyl]-2-methyl propoxy]methyl]quinolin-8-ol (TMOM5OX) towards Eu 3+ and Tb 3+ metal ions have been investigated by potentiometric, UV–vis and fluorescence spectrophotometric methods. TMOM5OX has been found to form two protonated complexes [Eu(H 5 L)] 5+ and [Tb(H 4 L)] 4+ below pH 2.3, which consecutively deprotonates through one and two-proton processes with rise of pH. The formation constants (log β 11 n ) of neutral complexes have been determined to be 35.24 and 35.23, and the pLn (pLn = −log[Ln 3+ ]) values of 16.63 and 18.57 for Eu 3+ and Tb 3+ ions, respectively, calculated at pH 7.4, indicating TMOM5OX is a good lanthanide synthetic chelator. The photophysical properties of novel quinoline-lanthanide systems were also scrutinized for photonics applications. The absorption spectroscopy of these complexes shows marked spectral variations due to characteristic lanthanide transitions, which support the use of TMOM5OX as a sensitive optical pH based sensor to detect Ln 3+ metal ions in biological systems. In addition, these complexes have also been shown to exhibit strong green fluorescence allowing simultaneous sensing within the visible region under physiological pH in competitive medium for both Eu(III) and Tb(III) ions. The intense fluorescence from these compounds were revealed to intermittently get quenched under acidic and basic conditions due to the photoinduced intramolecular electron transfer from excited 8-hydroxyquinoline (8-HQ) moiety to metal ion, just an opposite process. This renders these compounds the OFF–ON–OFF type of pH-dependent fluorescent sensor. The complexes coordination geometries were optimized using the sparkle/PM6 model and the theoretical spectrophotometric studies were carried out in order to validate the experimental findings, based on ZINDO/S methodology at configuration interaction with single excitations (CIS) level. These results clearly attest for the efficacy of the theoretical models employed in all calculations and create new interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

Experimental and theoretical approach of photophysical properties of lanthanum(III) and erbium(III) complexes of tris(methoxymethyl)-5-oxine podant

With the aim of evaluating the coordination behavior of a novel polydentate tripodal ligand, 5-[[3-[(8-hydroxy-5-quinolyl)methoxy]-2-[(8-hydroxy-5-quinolyl)methoxymethyl]-2-methyl propoxy]methyl]quinolin-8-ol (TMOM5OX), towards La(III) and Er(III) metal ions, the detailed investigations of photophysical properties by theoritical and experimental (potentiometric, UV–visible and fluorescence spectrophotometry) methods were carried out. TMOM5OX has been found to form protonated complex [Ln(H4L)]4+ (Ln=La or Er) below pH 3.8, which consecutively deprotonates through one-proton processes with rise of pH. The formation constants (logβ) of neutral complexes have been determined to be 36.42 (LaL) and 35.76, 37.62 (for ErL and ErL2, respectively) and the pLn (pLn=−log[Ln3+]) values of 24.6 and 27.1 for La(III) and Er(III) ions, respectively, calculated at pH 7.4, indicating TMOM5OX is a good lanthanide synthetic chelator. The absorption spectroscopy of these complexes show marked spectral variations due to characteristic lanthanide transitions, which support the use of TMOM5OX as a sensitive optical pH based sensor to detect Ln(III) metal ions in biological systems. In addition, these complexes have also been shown to exhibit strong green fluorescence allowing simultaneous sensing within the visible region under physiological pH in competitive medium for both La(III) and Er(III) ions. The intense fluorescence from these compounds were revealed to intermittently get quenched under acidic and basic conditions due to the photoinduced intramolecular electron transfer from excited 8-hydroxyquinoline (8-HQ) moiety to metal ion, just an opposite process. This renders these compounds the OFF–ON–OFF type of pH-dependent fluorescent sensors. The complexes coordination geometries were optimized using the sparkle/PM6 model and the theoretical spectrophotometric studies were carried out in order to validate the experimental findings, based on ZINDO/S methodology at configuration interaction with single excitations (CIS) level. These results clearly attest for the efficacy of the theoretical models employed in all calculations and create new interesting possibilities for the design in-silico of novel and highly efficient lanthanide–organic frameworks.

Theoretical Study on the Excited Electronic States of Coronene and Its π-Extended Molecules Using the Symmetry-Adapted Cluster-Configuration Interaction Method

Abstract The excited electronic states and optical absorption spectra of coronene (C24H12), hexa-peri-hexabenzocoronene (HBC) (C42H18), and circumcoronene (C54H18) were studied using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. For coronene and HBC, the SAC-CI calculations reproduced the experimental spectra well and predicted optically forbidden excited states. For HBC, the symmetry lowering enhanced the intensity of the S2 state that corresponds to the p-band, and the SAC-CI calculation predicted the existence of the second and third optically allowed states around the β-band region near 4.0 eV. For circumcoronene, the SAC-CI calculation predicted a strong absorption of the β-band in the visible light region. The mechanisms of energy splitting for the HOMO–LUMO transition were investigated. Electron correlation was the most important factor for the energy splitting between the lowest and the next-lowest states. Configuration interaction with single excitations (CIS) calculations could not correctly predict the relative energies of these states in coronene and circumcoronene. For HBC, on the other hand, the CIS calculation provided the same energy order as the SAC-CI calculation.

Substituent and Solvent Effects on Electronic Structure and Spectral Property of ReCl(CO)3(N∧N) (N∧N = Glyoxime): DFT and TDDFT Theoretical Studies

The ground- and excited-state structures of five Re(I) halide glyoxime complexes ReCl(CO)(3)(N(∧)N) (N(∧)N = glyoxime (DHG 1), dimethylglyoxime (DMG 2), cyclohexane dione glyoxime (CHDG 3), dibromoglyoxime (DBG 4), and dimethylformylgloxime (DMFG 5)) have been studied with density functional theory (DFT) and configuration interaction with single excitations (CIS) methods. Time-dependent density functional theory/polarized continuum model (TDDFT/PCM) was carried out to predict the absorption and emission spectra in different media. The effect of substituent and solvent has been researched. It is found that electron-donating groups increase the lowest unoccupied molecular orbital (LUMO) energy resulting in the increased highest occupied molecular orbital (HOMO)-LUMO energy gap. The change leads to their absorption spectra blue shifts in the order 1 > 2 > 3, which arises from the HOMO-1 → LUMO. Just the opposite, electron-withdrawing groups lead to the spectra red shifts (5 > 4 > 1) because of the decreased HOMO-LUMO energy gap. The reorganization energy (λ) calculations show that the relatively balanceable charges transfer abilities of 2 will result in the higher efficiency of organic light emitting devices (OLEDs). In addition, both the absorption and the emission spectra display red shifts in different extents with the decrease of solvent polarity.

Solvent-Induced Frequency Shifts: Configuration Interaction Singles Combined with the Effective Fragment Potential Method

The simplest variational method for treating electronic excited states, configuration interaction with single excitations (CIS), has been interfaced with the effective fragment potential (EFP) method to provide an effective and computationally efficient approach for studying the qualitative effects of solvents on the electronic spectra of molecules. Three different approaches for interfacing a non-self-consistent field (SCF) excited-state quantum mechanics (QM) method and the EFP method are discussed. The most sophisticated and complex approach (termed fully self consistent) calculates the excited-state electron density with fully self-consistent accounting for the polarization (induction) energy of effective fragments. The simplest approach (method 1) includes a strategy that indirectly adds the EFP perturbation to the CIS wave function and energy via modified Hartree-Fock molecular orbitals, so that there is no direct EFP interaction with the excited-state density. An intermediate approach (method 2) accomplishes the latter in a noniterative perturbative manner. Theoretical descriptions of the three approaches are presented, and test results of solvent-induced shifts using methods 1 and 2 are compared with fully ab initio values. These comparisons illustrate that, at least for the test cases examined here, modification of the ground-state Hartree-Fock orbitals is the largest and most important factor in the calculated solvent-induced shifts. Method 1 is then employed to study the aqueous solvation of coumarin 151 and compared with experimental measurements.

Electronic Structures and Optical Properties of Indolocarbazole Isomers

Density functional theory(DFT) and the configuration interaction with single excitations(CIS) method were used to optimize the ground state and excited state structures of five indolocarbazole molecules using the 6-31G(d,p) basis set.Based on their geometric structures,the absorption and emission spectra were calculated using time-dependent DFT(TD-DFT) with the same basis set and employing the polarizable continuum medium model(PCM).There are obvious differences in the emission spectra of these isomers as isomer 5 has larger oscillator strength in its emission spectrum,but its transition energies are the lowest among the isomers.The emission peak value of isomer 4 is the highest and the oscillator strengths of isomer 2 are the weakest from 250 to 450 nm.This is because the structures change from ground state to the excited state and the molecular orbital(MO) energy levels of these molecules are different.We also evaluated the nonlinear optical response(first hyperpolarizability) of this series of molecules.The calculated polarizabilities are similar but the static first hyperpolarizabilities(β0) are different.The β0 of isomer 2 is the largest among the compounds investigated.

Photophysical Properties of 1,3,5-Tris(2-naphthyl)benzene and Related Less-Arylated Compounds: Experimental and Theoretical Investigations

Recently, a growing interest has concerned compounds characterized by high chemical and photophysical stability and high quantum yield for their possible technological applications. 1,3,5-Tris(2-naphthyl)benzene (N3B), 1,3-bis(2-naphthyl)benzene (N2B), and 2-naphthyl-benzene (N1B) are promising compounds, but they needed a detailed photophysical characterization. In this context, theoretical and experimental investigations have been carried out. Steady-state and decay time fluorescence measurements indicate that the second naphthyl group, added in the meta position of N1B, perturbs the electronic levels, whereas the further naphthyl addition, leading to N3B, does not promote changes in all of the observed properties. The investigated compounds show a biexponential fluorescence decay that has been attributed to a rearrangement involving the exited states S(1) and S(2). The minimum structure corresponding to the S(1) and S(2) states has been obtained at the configuration interaction with single excitations (CIS) level of theory. For the ground-state geometry, a conformational analysis at the Hartree-Fock level has also been carried out. We have evaluated the energy gaps between electronic levels by using Zerner's intermediate neglect of differential overlap (ZINDO) method. The species involved in the fluorescence have been experimentally characterized, and the decay-associated spectra have been obtained.

Tuning Fluorescence Lifetimes through Changes in Herzberg−Teller Activities: The Case of Triphenylene and Its Hexamethoxy-Substituted Derivative

The fluorescence spectra of triphenylene (TP) and 2,3,6,7,10,11-hexamethoxy-triphenylene (HMTP) are measured in glass matrices, and the vibronic structure associated with the electronic spectra is simulated with the help of quantum chemically computed molecular parameters. Franck-Condon (FC) and Herzberg-Teller (HT) mechanisms are included. For excited-state calculations, both configuration interaction with single excitations (CIS) and time-dependent density functional theory (TDDFT) are employed. It is shown that the FC activity is associated with modes of similar shape and frequency in both molecules, while the HT-induced false origins with the largest activity are associated with rather different frequencies and normal coordinates as a result of the mixing and energy lowering of the low-lying allowed excited states in HMTP. The increased HT activity explains the reduced S(1) state lifetime in the substituted TP, in turn driven by the excited-state rearrangement occurring upon substitution of the TP core.

Computational Prediction of Absorbance Maxima for a Structurally Diverse Series of Engineered Green Fluorescent Protein Chromophores

By virtue of its self-sufficiency to form a visible wavelength chromophore within the confines of its tertiary structure, the Aequorea victoria green fluorescent protein (GFP) is single-handedly responsible for the ever-growing popularity of fluorescence imaging of recombinant fusion proteins in biological research. Engineered variants of GFP with altered excitation or emission wavelength maxima have helped to expand the range of applications of GFP. The engineering of the GFP variants is usually done empirically by genetic modifications of the chromophore structure and/or its environment in order to find variants with new photophysical properties. The process of identifying improved variants could be greatly facilitated if augmented or guided by computational studies of the chromophore ground and excited-state properties and dynamics. In pursuit of this goal, we now report a thorough investigation of computational methods for prediction of the absorbance maxima for an experimentally validated series of engineered GFP chromophore analogues. The experimental dataset is composed of absorption maxima for 10 chemically distinct GFP chromophore analogues, including a previously unreported Y66D variant, measured under identical denaturing conditions. For each chromophore analogue, excitation energies and oscillator strengths were calculated using configuration interaction with single excitations (CIS), CIS with perturbative correction for double substitutions [CIS(D)], and time-dependent density functional theory (TD DFT) using several density functionals with solvent effects included using a polarizable continuum model. Comparison of the experimental and computational results show generally poor quantitative agreement with all methods attempted. However, good linear correlations between the calculated and experimental excitation energies (R2>0.9) could be obtained. Oscillator strengths obtained with TD DFT using pure density functionals also correlate well with the experimental values. Interestingly, most of the computational methods used in this work fail in the case of nonaromatic Y66S and Y66L protein chromophores, which may be related to a significant contribution of double excitations to their excited-state wavefunctions. These results provide an important benchmark of the reliability of the computational methods as applied to GFP chromophore analogues and lays a foundation for the computational design of GFP variants with improved properties for use in biological imaging.

Theoretical study on the structures and electronic spectra of novel quinoid 1,3,4-oxadiazole derivatives

The B3LYP and PBE1PBE methods with the 6-31G ∗ basis set have been used to compute the ground state geometries, electronic structures and IR spectra of novel quinoid 1,3,4-oxadiazole derivatives. The lowest singlet excited state geometries of these compounds were optimized by the configuration interaction with single excitations (CIS) method. The absorption and emission spectra were calculated by time-dependent density functional theory (TDDFT) on the basis of the ground and excited state optimized geometries, respectively. Solvent effects on the excitation energies were computed through the integral equation formalism of the polarizable continuum model (IEFPCM). The quinoid structure in ααα′α′-tetra(4- tert-butylphenyl)-1,3,4-oxadiazolequinodimethane (TPOQ) was further identified by calculating the structural parameters of the ground state geometry and its IR spectra. Through the analysis of charge distribution in model compounds bearing aromatic groups with different electron-donor abilities, an intramolecular charge transfer has been confirmed, which plays an important role in the light-emitting properties. TDDFT calculations revealed that the maximal absorptions of all these quinoid derivatives originate from the π–π ∗ transition from HOMO to LUMO. The calculated absorption and emission spectral properties of TPOQ are in good agreement with the experimental results.

Time-Dependent Density Functional Theory Study of the Al Complexes with Aromatic Ligands for Blue Organic Light-Emitting Diodes

Aluminum(III) complexes with 8-hydroxyquinoline have attracted much attention because of their potential application in organic light emitting diodes (OLEDs) as green and blue emitting materials with the subtle effect of the substitution on the fluorescence and electroluminescent (EL) properties. The photoluminescence of aluminum(III) complexes [(tri(2′,2-dihydroxybiphenyl) aluminum(III)] have been studied as efficient fluorescence emitting materials [17]. In this paper, geometric and electronic properties of several Al complexes are studied to find the ligand effect related to the intensities of their absorptions and emissions using computational methods. In order to find a new highly efficient blue emitting materials, we have designed new Al complexes with aromatic ligands, [4,5-phenanthrenediol, 3,3′-dihydroxy-2,2′-binaphthalene, 2-(2′-phenol)-2-naphthol, and 1-(2′-phenol)-2-naphthol]. The geometry optimizations of the ground and the lowest excited electronic states were determined using HF/3-21G(d) and configuration interaction with single excitations (CIS) method. The vertical and adiabatic transition energies were calculated using time-dependent density functional theory (TD-DFT) with B1LYP/6-31G(d). As a result, we propose new blue fluorescent Al complexes of high luminescence efficiency.

Theoretical investigation of tetra-substituted pyrenes for organic light emitting diodes

Abstract Pyrene derivatives have been developed to blue fluorescent light emitting materials for organic light emitting diodes (OLEDs). Luminescence efficiency of pyrene molecule is very low, however pyrenes substituted with large group can give a bright blue fluorescence. Substituted pyrenes were investigated to increase luminescence efficiency and color purity. In this paper, we studied 1,3,6,8-tetra-substituted pyrenes theoretically. The investigation was studied by ab initio method. Density functional theory (DFT) utilizing the B3LYP functional with the 6-31G(d) basis set was used for energy calculation and geometry optimization of the ground electronic state of those compounds. The geometry optimization of the first excited electronic states was determined using configuration interaction with single excitations (CIS) method. Energies of vertical and adiabatic transition were calculated using time-dependent density functional theory (TD-DFT) with B3LYP/6-31G(d) calculation. The investigation on 1,3,6,8-tetra-substituted pyrenes with the effect of the aromatic substituents showed that the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was decreased as the conjugation length was increased. This trend was also appeared when the nitrogen atom was substituted with carbon atom in the aromatic substituents. Also the substituted pyrenes with large moieties were slightly distorted from the planar structure. Thus, the luminescent efficiencies of tetra-substituted pyrenes were increased more than that of the pyrene molecule. In this paper, t(dpe)py molecule was proposed as a new efficient blue emitter for OLED from calculated result.

Computations on the ÖX̃ transition of isoprene‐OH‐O2 peroxy radicals

Calculations are carried out on the A state of HO2, CH3O2, and CH3CH2O2 and 10 isomers and conformers of the isoprene-OH-O2 peroxy radicals derived from OH addition to isoprene (2-methyl-1,3-butadiene). In addition to calculating vertical and adiabatic excitation energies, we consider the effect of excitation on molecular structure, and examine the OO stretching frequencies, which are known to be major features in the absorption spectra of the A states of the smaller radicals. The two methods used are the configuration interaction with single excitations (CIS) method and time-dependent density functional theory (TD-DFT), both with a range of basis sets up to 6-311++G(2df,2pd). TD-DFT overestimates excitation energies considerably, while CIS tends to underestimate them slightly. TD-DFT does seem to capture the trend in excitation energy vs. size for the smaller peroxy radicals. Conformation and configuration strongly affect the excitation energies of the peroxy radicals from isoprene. CIS calculations indicate that the intramolecular OH--O hydrogen bonds, present in the ground state of some peroxy radicals from isoprene, are weakened or broken in the excited state, while TD-DFT calculations suggest they are retained.

Ab initio analysis of some fluoride and oxide structures doped with Pr and Yb

AbstractDoping effects are analyzed by means of the ab initio perturbed ion (aiPI) method via substitution of the fluorides and oxides of zirconium, hafnium, and thorium. Lattice relaxation is simulated through the calculation of vibrational breathing modes and substitutional effects on the compound are thereby analyzed. In addition, the band gaps (in the pure species) and impurity levels (where substitutional ions Pr+4 and Yb+3 are considered in the doped species) of the fluorides are estimated via the transition energy calculated at the aiPI‐optimized geometry of the pure and doped crystal clusters by means of the configuration interaction with single excitations (CIS) method that accounts for electronic correlation. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Spectroscopy and Photochemistry of Phenylacetic Acid Esters and Related Substrates. The Stereoelectronic Dependence of the Aryl/Carboxyl Bichromophore Interaction

The 254-nm-initiated Norrish Type II photofragmentation of the ethoxyethyl esters of a series of phenylacetic acids (1b-4b) has been studied in order to further elaborate the aryl/ester interaction that is photochemically and photophysically evident in these systems. The ethoxyethyl ester of benzonorbornene-1-carboxylic acid (5) has also been prepared and studied, as has a rigid tricyclic lactone (6) which places the chromophores in an optimal stereoelectronic relationship for interaction. The experimental work is accompanied by Hartree-Fock (HF), Natural Bond Orbital (NBO), and Configuration Interaction with Single Excitations (CIS) calculations on the methyl esters of phenylacetic acid (1a) and α-methoxyphenylacetic acid (4a)

Electronic energies, dipole moment matrix elements, and static polarizabilities and hyperpolarizabilities for some diphenyl molecules

The "giant dipole" molecules, NR1R2—C6H4—(C≡C)n—C6H4—NO2n = 0, 1, 2, are studied theoretically for three sets of substituents: R1 = R2 = H, R1 = H, R2 = CH3, and R1 = R2 = CH3. For each of these nine molecules, the energies, and permanent and transition dipole moments for the 20 lowest electronic states are calculated using the intermediate neglect of differential overlap (INDO) approximation at the configuration interaction with single excitations (CIS) level. Static polarizabilities and hyperpolarizabilities for the ground states are reported for these "push–pull" molecules. The changes in the physical properties of interest due to increase in conjugation length and the inductive effect of substituents on the donor group attached to the rings are discussed. The energies and permanent and transition dipole moments for the ten lowest electronic states are tabulated for use in future studies of the spectral and dynamical effects of permanent dipoie moments on laser-induced one- and multi-photon electronic transitions in realistic models for many-level giant dipole molecules.