Efficient pole‐search algorithm for dynamic polarizability: Toward alternative excited‐state calculation for large systems

This study presents an efficient algorithm to search for the poles of dynamic polarizability to obtain excited states of large systems with nonlocal excitation nature. The present algorithm adopts a homogeneous search with a constant frequency interval and a bisection search to achieve high accuracy. Furthermore, the subtraction process of the information about the detected poles from the total dynamic polarizability is used to extract the undetected pole contributions. Numerical assessments confirmed the accuracy and efficiency of the present algorithm in obtaining the excitation energies and oscillator strengths of all dipole‐allowed excited states. A combination of the present pole‐search algorithm and divide‐and‐conquer‐based dynamic polarizability calculations was found to be promising to treat nonlocal excitations of large systems. © 2016 Wiley Periodicals, Inc.     

Quantum Monte Carlo study of ground and first excited state of C,N, O,F, and Ne atoms using Slater-Jastrow-Backflow wave function

All-electron fixed-node diffusion quantum Monte Carlo energies of the two lowest-lying states of C, N, O, F, and Ne atoms are reported. The Slater-Jastrow form is used as the trial wave function. We will use single- and multideterminant wave functions as the Slater part. The single-determinant wave function has been computed by the Hartree-Fock method and the multideterminant wave functions have been computed by the complete active space self-consistent field, configuration interaction with single and double excitation, configuration interaction with single, double, triple, and quadruple excitation and second-order configuration interaction. For the ground- and first excited states, the multideterminant wave functions have computed more than 99% of the correlation energy. Significant improvements have been achieved using the backflow transformations and up to 99.8% of the correlation energy has been recovered. A very good agreement with the experimental data has been obtained for the excitation energies.     

Correlation of ground and excited state dissociation constants of trans -para- and ortho-substituted cinnamic acids

The ground and excited state dissociation constants oftrans- para- and ortho-substituted cinnamic acids have been determined in 50% (v/v) dioxan-water mixture at 30°C using the Forster cycle. The measured dissociation constants are analysed in the light of single and dual substituent parameter (DSP) equations. Excited state dissociation constants ofp-substituted cinnamic acids correlate well with the exalted substituent constants. The DSP method of analysis shows that resonance effect is predominant relative to inductive effect in the excited state than in the ground state for the para-substituted acids. The single parameter equation gives poor correlation for the ortho-substituted acids. However, the DSP analysis shows fairly good correlation. The inductive effect is predominant relative to the resonance effect in the excited state than in the ground state     

Discrete contributions to static dipole polarizabilities of excited bound states of non-relativistic hydrogen-like atoms

The static dipole polarizability α _{d, i} for an arbitrary bound state i of the non-relativistic hydrogen-like atom has been known for a long time from, e.g; the second-order perturbation theory treatment of the Stark effect. A reliable result for the ground state requires both summation over the discrete spectrum and inclusion of the continuum contribution. This continuum contribution is known to decrease for excited states, but a systematic study of this decrease has not been available so far. We present here representative results from a systematic study of α _{d, i} , which was performed as a first test of a new algorithm for the radial integrals involved. Partial sum approximations of the discrete contribution yield the total α _{d, i} with a relative error of less than 1% for all states i with principal quantum number n≥5. Corresponding results for the relativistic case, for which the radial integral algorithm was developed, will be presented elsewhere. Dedicated to Professor Hermann Stoll on the occasion of his 60th birthday An erratum to this article is available at .     

2-甲基环戊酮离子前6个激发态的解离

用量子化学原理,CIS/6-31+G(d,p)方法研究了2-甲基环戊酮离子前6个激发态的解离过程,通过虚频的振动分析,计算其可能产物,寻求2-甲基环戊酮离子的解离通道和解离产物.     

Dynamic dipole polarizabilities of the ground and excited states of confined hydrogen atom computed by means of a mapped Fourier grid method

Accurate theoretical estimates of static and dynamic dipole polarizabilities are reported for the ground and excited states of hydrogen atom confined at the center of a spherical “box” with impenetrable walls using a novel theoretical algorithm that combines the variational–perturbation approach with an appropriately adapted mapped Fourier grid method and uniformly maintains the numerical accuracy. A variation of computed polarizabilities is observed as a function of the number of grid points. However, rapid convergence to their correct values, even far into the anomalous dispersion region, is achieved by an extrapolation procedure to the limit of an infinitely large number of grid points using a small number of the lowest‐order Padé approximants. It is shown that dipole polarizabilities strongly depend upon the electronic state and the radius of confinement. In particular, the static polarizability of 2s state changes sign under strong confinement. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

四氰基乙烯—四甲基乙烯体系光诱导电子转移的溶剂效应及电荷分离激发态研究

用从头算方法,在HF/6-31 G^**和CASSCF（8,8）/6-31G^*基组水平上对四氰基乙烯与四甲基乙烯间电子转移的溶剂效应及电荷分离激发态进行了理论计算与研究。通过对给、受体各种几何构型的优化,计算了孤立给、受体之间的电荷分离反应热。在假定碰撞络合物形成过程中给、受体内部结构不发生变化的前提下,通过优化给、受体中心间距的方法,找出了络合物的稳定构型。计算了水溶剂及二氯甲烷溶剂中两种稳定构型络合物的电荷分离激发态,计算结果表明光激发可以直接导致体系的电荷分离。     

Time‐dependent density functional theory study on the hydrogen bonding‐induced twisted intramolecular charge‐transfer excited states of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine

In this work, the time‐dependent density functional theory (TDDFT) method was carried out to investigate the hydrogen‐bonded intramolecular charge‐transfer excited state of 2‐(4′‐N,N‐dimethylaminophenyl)imidazo[4,5‐b]pyridine (DMAPIP) in methanol (MeOH) solvent. All the geometric conformations of the ground state and locally excited (LE) state and the twisted intramolecular charge‐transfer (TICT) state for isolated DMAPIP and its hydrogen‐bonded complexes have been optimized. At the same time, the absorption and fluorescence spectra of DMAPIP and the hydrogen‐bonded complexes in different electronic states are also calculated. We theoretically demonstrated for the first time that the intermolecular hydrogen bond formed between DMAPIP and MeOH can induce the formation of the TICT state for DMAPIP in MeOH solvent. Therefore, the two components at 414 and 506 nm observed in the fluorescence spectra of DMAPIP in MeOH solvent were reassigned in this work. The fluorescence peak at 414 nm is confirmed to be the LE state. Furthermore, the red‐shifted shoulder at 506 nm should be originated from the hydrogen‐bonded TICT excited state. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Sensitization mechanisms from excited‐singlet state of pyrromethene dye to a radical‐generating reagent in a poly(methylmethacrylate) film

The sensitization mechanisms of a pyrromethene dye with a radical‐generating reagent, 3,5,3′,5′‐tetramethylpyrromethene‐BF₂ (BH) with 3,3′,4,4′‐tetrakis(t‐butyldioxycarbonyl)benzophenone (BP), in a poly‐ (methylmethacrylate) (PMMA) film were investigated by laser flash phoptolysis using a total reflection cell and single photon counting. From the laser flash photolysis, strong fluorescence was detected though no transient absorption was detected. The fluorescence intensity was significantly decreased with increasing concentration of BP, apparently exhibiting Perrin‐type static quenching at a quenching radius, R_f = 26 Å. From the examination of decay profile using single photon counting, logarithmic plots of fluorescence decay in a PMMA film afforded a nonlinear, convex reduction, corresponding to a streched exponential decay, while the logarithmic plots in acetonitrile showed a linear relationship. With increasing concentration of BH, the fluorescence maximum was shifted to red, and the intensity of fluorescence was significantly reduced. The red shift of fluorescence, the nonlinear fluorescence logarithmic decay and the large reduction in fluorescence indicate a dispersive photoexcited state and a relaxation of excitation energy hopping across an array of sites with Gaussian energy distribution. Moreover, after incorporating BP, the convex logarithmic plots became more steep, and the fluorescence maximum was also shifted to red, exhibiting a nonstatic quenching process competitive to the excitation energy hopping. Thus the sensitization of photoinitiator system containing BH and BP, whose contents were almost same as that in the commercial products, was due to a static quenching process from dispersive singlet excited BH to BP ground state, and the nonstatic quenching process competitive to the excitation energy hopping was minimal. Copyright © 1999 John Wiley & Sons, Ltd.     

Ground and low‐lying excited C2v states of FeO2—A challenge to computational methods

DFT (BPW91 and B3PW91), CCSD, CCSD(T), and MP2 geometry optimizations were performed on the lowest A₁, A₂, B₁, and B₂ singlet to septet states (a total of 16 states) of FeO₂, using in most cases the 6‐311+G(3df) basis set. With few exceptions, the different methods led to similar geometries. The lowest state is ³B₁ or ⁵B₂, depending on the method used. The quality of the various computational methods was tested by a comparison of vertical excitation energies with corresponding high‐level MRCI values. The best agreement with MRCI was found for BPW91 and B3PW91, with average deviations of about 0.2 eV. MRCI calculations were carried to extremely low configuration selection thresholds (0.025 μh) in order to find the lowest state of FeO₂. The full CI estimate (including Davidson correction and energy extrapolation to 0 μh) gave ³A₁ as the lowest state, followed by ⁵B₂ (0.03 eV) and ³B₁ (0.06 eV). Both ³B₁ and ³A₁ have geometries and vibrational frequencies consistent with the observed IR spectrum. The calculated adiabatic electron affinity of FeO₂ (from ³B₁ of FeO₂ to ⁴B₂ of FeO) is 2.46 eV with CCSD(T), and 2.22 eV with BPW91, compared with the experimental value of 2.36 eV. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Molecule‐specific determination of atomic polarizabilities with the polarizable atomic multipole model

Recently, many polarizable force fields have been devised to describe induction effects between molecules. In popular polarizable models based on induced dipole moments, atomic polarizabilities are the essential parameters and should be derived carefully. Here, we present a parameterization scheme for atomic polarizabilities using a minimization target function containing both molecular and atomic information. The main idea is to adopt reference data only from quantum chemical calculations, to perform atomic polarizability parameterizations even when relevant experimental data are scarce as in the case of electronically excited molecules. Specifically, our scheme assigns the atomic polarizabilities of any given molecule in such a way that its molecular polarizability tensor is well reproduced. We show that our scheme successfully works for various molecules in mimicking dipole responses not only in ground states but also in valence excited states. The electrostatic potential around a molecule with an externally perturbing nearby charge also exhibits a near‐quantitative agreement with the reference data from quantum chemical calculations. The limitation of the model with isotropic atoms is also discussed to examine the scope of its applicability. © 2012 Wiley Periodicals, Inc.     

Crystallization‐Induced Reversal from Dark to Bright Excited States for Construction of Solid‐Emission‐Tunable Squaraines

Squaraines (SQs) with tunable emission in the solid state is of great importance for various demands; however a remaining challenge is emission quenching upon aggregation. Herein, a unique SQ, named as CIEE‐SQ, is designed to exhibit strong emission in crystal, undergoing crystallization‐induced reverse from dark ¹(n+σ,π*) to bright ¹(π,π*) excited states. Such an excited state of CIEE‐SQ can be subtly tuned by molecular conformation changes during the unexpected temperature‐triggered single‐crystal to single‐crystal (SCSC) reversible transformation. Furthermore, co‐crystallization between CIEE‐SQ and chloroform largely stabilize the ¹(π,π*) state, enhancing the transition dipole moment and decreasing the reorganization energy to boost the fluorescence, which is promising in data encryption and decryption.     

Ab initio QM/MM study of excited state electron transfer between pyrene and 4,4′‐bis(dimethylamino)‐diphenylmethane with different solvent systems: Role of hydrogen bonding within solvent molecules

The exciplex is a charge transfer species formed in the process of electron transfer between an electron donor and an electron acceptor and hence is very sensitive to solvent polarity. In order to understand the role of solvent in exciplex formation between pyrene (PY) and 4,4′‐bis(dimethylamino)diphenylmethane (DMDPM), we used two types of solvent approximations: an implicit solvent model and an explicit solvent model. The difference in energies between the excited and the meta‐stable Frank–Condon state (ΔE) of the structures were assumed to correspond to the emission maximum of the exciplex in different solvents. The ΔE values show the trend of stabilization of the exciplex with an increase in solvent polarity. This trend in stabilization is substantially more prominent in the explicit solvent model than that with the implicit solvent model. The ΔE value obtained in methanol reflects equal stabilization compared to that in a more polar solvent, N,N‐dimethylformamide. This extra stabilization of the exciplex may be explained on the basis of the H‐bonding capability of the protic solvent, methanol. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Investigation of excited‐state properties of fluorene–thiophene oligomers by the SAC‐CI theoretical approach

Excited states of fluorene‐ethylenedioxythiophene (FEDOT) and fluorene‐S,S‐dioxide‐thiophene (FTSO2) monomers and dimers were studied by the symmetry‐adapted cluster (SAC)‐configuration interaction (CI) method. The absorption and emission peaks observed in the experimental spectra were theoretically assigned. The first three excited states of the optimized conformers, and the conformers of several torsional angles, were computed by SAC‐CI/D95(d). Accurate absorption spectra were simulated by taking the thermal average for the conformers of torsional angles from 0° to 90°. The conformers of torsional angles 0°, 15°, and 30° mainly contributed to the absorption spectra. The full width at half‐maximum of the FEDOT absorption band is 0.60 eV (4839 cm^?1), which agrees very well with the experimental value of 0.61 eV (4900 cm^?1). The maximum absorption wavelength is located at 303 nm, which is close to those of the experimental band (327 nm). The calculated absorption spectrum of FTSO2 showed two bands in the range of 225–450 nm. This agrees very well with the available experimental spectrum of a polymer of FTSO2, where two bands are detected. The excited‐state geometries were investigated by CIS/6‐31G(d). These showed a quinoid‐type structure which exhibited a shortening of the inter‐ring distance (0.06 Å for FEDOT and 0.04 Å for FTSO2). The calculated emission energy of FEDOT is 3.43 eV, which agrees very well with the available experimental data (3.46 eV). The fwhm_E is about 0.49 eV (3952 cm^?1), while the experimental fwhm is 0.43 eV (3500 cm^?1). For FTSO2, two bands were also found in the emission spectrum. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Prediction of spectroscopic constants for diatomic molecules in the ground and excited states using time-dependent density functional theory

Spectroscopic constants of the ground and next seven low-lying excited states of diatomic molecules CO, N2, P2, and ScF were computed using the density functional theory SAOP/ATZP model, in conjunction with time-dependent density functional theory (TD-DFT) and a recently developed Slater type basis set, ATZP. Spectroscopic constants, including the equilibrium distances r(e), harmonic vibrational frequency omega(e), vibrational anharmonicity omega(e)x(e), rotational constant B(e), centrifugal distortion constant D(e), the vibration-rotation interaction constant alpha(e), and the vibrational zero-point energy E(n)0 were generated in an effort to establish a reliable database for electron spectroscopy. By comparison with experimental values and a similar model with an established larger Slater-type basis set, et-QZ3P-xD, it was found that this model provides reliably accurate results at reduced computational costs, for both the ground and excited states of the molecules. The over all errors of all eight lowest lying electronic states of the molecules under study using the effective basis set are r(e)(+/-4%), omega(e)(+/-5% mostly without exceeding +/-20%), omega(e)x(e)(+/-5% mostly without exceeding 20%, much more accurate than a previous study on this constant of +/-30%), B(e)(+/-8%), D(e)(+/-10%), alpha(e)(+/-10%), and E(n)0(+/-10%). The accuracy obtained using the ATZP basis set is very competitive to the larger et-QZ3P-xD basis set in particular in the ground electronic states. The overall errors in r(e), omega(e)x(e), and alpha(e) in the ground states were given by +/-0.7, +/-10.1, and +/-8.4%, respectively, using the efficient ATZP basis set, which is competitive to the errors of +/-0.5, +/-9.2, and +/-9.1%, respectively for those constants using the larger et-QZ3P-xD basis set. The latter basis set, however, needs approximately four times of the CPU time on the National Supercomputing Facilities (Australia). Due to the efficiency of the model (TD-DFT, SAOP and ATZP), it will be readily applied to study larger molecular systems.     

Theoretical study of the excited‐state double proton transfer in the (3‐methyl‐7‐azaindole)‐(7‐azaindole) heterodimer

Excited‐state double proton transfer (ESDPT) in the (3‐methyl‐7‐azaindole)‐(7‐azaindole) heterodimer is theoretically investigated by the long‐range corrected time‐dependent density functional theory method and the complete‐active‐space second‐order perturbation theory method. The calculated potential energy profiles exhibit a lower barrier for the concerted mechanism in the locally excited state than for the stepwise mechanism through the charge‐transfer state. This result suggests that the ESDPT in the isolated heterodimer is likely to follow the former mechanism, as has been exhibited for the ESDPT in the homodimer of 7‐azaindole. © 2012 Wiley Periodicals, Inc.     

Probing the acidity of p-substituted phenols in the excited state: electronic spectroscopy of the p-cyanophenol-water cluster.

The hydrogen bond structure of the p-cyanophenol-water cluster has been determined in the ground and first excited electronic state by rotationally resolved UV spectroscopy. The water molecule is trans-linearly bound to the hydroxy group of the p-cyanophenol moiety, with hydrogen bond distances considerably shorter in both electronic states than in the similar phenol-water cluster. The structure of the cluster has been elucidated by ab initio calculations at various levels of theory and compared to the experimental findings. The barriers to internal rotation of the water moiety were determined experimentally to be 275 and 183 cm(-1) for the ground and excited state, respectively. Hydrogen bond distances and the energy barrier to water torsion correlate with the pK(a) values of different substituted phenols for both electronic states.