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Three‐dimensional accurate potential energy surfaces around the local minima of NO2− and NO2 were calculated with the SAC/SAC‐CI analytical energy gradient method. Therefrom, the ionization photoelectron spectra of NO2−, the equilibrium geometries and adiabatic electron affinity of NO2, and the vibrational frequencies including harmonicity and anharmonicity of NO2− and NO2 were obtained. The calculated electron affinity was in reasonable agreement with the experimental value. The SAC‐CI photoelectron spectra of NO2− at 350 K and 700 K including the rotational effects were calculated using the Franck–Condon approximation. The theoretical spectra reproduced well the fine experimental photoelectron spectra observed by Ervin et al. (J. Phys. Chem. 1988, 92, 5405). The results showed that the ionizations from many vibrational excited states as well as the vibrational ground state are included in the experimental photoelectron spectra especially at 700 K and that the rotational effects are important to reproduce the experimental photoelectron spectra of both temperatures. The SAC/SAC‐CI theoretical results supported the analyses of the spectra by Ervin et al., except that we could show some small contributions from the asymmetric‐stretching mode of NO2−. © 2018 Wiley Periodicals, Inc. The SAC‐CI theoretical photoelectron spectra including the rotational effects have reproduced well the fine experimental photoelectron spectra of NO2− at both 350 K and 700 K observed by Ervin et al. [ABSTRACT FROM AUTHOR]

Unlike π-electron chromophores, the peralkylated n-tetrasilane σ-electron chromophore resembles a chameleon in that its electronic spectrum changes dramatically as its silicon backbone is twisted almost effortlessly from the syn to the anti conformation (changing the SiSiSiSi dihedral angle ω from 0 to 180°). A combination of UV absorption, magnetic circular dichroism (MCD), and linear dichroism (LD) spectroscopy on conformationally controlled tetrasilanes 1- 9, which cover fairly evenly the full range of angles ω, permitted a construction of an experimental correlation diagram for three to four lowest valence electronic states. The free chain tetrasilane n-Si4Me10 ( 10), normally present as a mixture of three enantiomeric conformer pairs of widely different angles ω, has also been included in our study. The spectral trends are interpreted in terms of avoided crossings of 1B with 2B and 2A with 3A states, in agreement with SAC-CI calculations on the excited states of 1- 7 and conformers of 10. [ABSTRACT FROM AUTHOR]

O1s core-electron binding energies (CEBE) of the atomic oxygens on different Ag surfaces were investigated by the symmetry adapted cluster-configuration interaction (SAC-CI) method combined with the dipped adcluster model, in which the electron exchange between bulk metal and adsorbate is taken into account properly. Electrophilic and nucleophilic oxygens ( Oelec and Onuc) that might be important for olefin epoxidation in a low-oxygen coverage condition were focused here. We consider the O1s CEBE as a key property to distinguish the surface oxygen states, and series of calculation was carried out by the Hartree-Fock, Density functional theory, and SAC/SAC-CI methods. The experimental information and our SAC/SAC-CI results indicate that Oelec is the atomic oxygen adsorbed on the fcc site of Ag(111) and that Onuc is the one on the reconstructed added-row site of Ag(110) and that one- and two-electron transfers occur, respectively, to the Oelec and Onuc adclusters from the silver surface. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The free complement (FC) method, or the free iterative-complement-interaction (ICI) method, for generating the exact wave function from an approximate initial wave function has been applied to the hydrogen atom starting from the Slater and Gaussian functions for comparison. The process of improvement was followed by checking the wave function itself and other quantities that have definite exact values. Because the exact wave function is simple in this case, we could make clear analyses for many aspects of the wave function. We examined the energy, the wave function itself, the wave function error, the H-square error, the local energy near the nucleus, and the cusp. Both the Slater and Gaussian functions gave similar convergence rates to the exact function with respect to the order of the FC method, but the number of complement functions at a particular order is three times larger for the Gaussian case than for the Slater case. Although the cusp value of the Gaussian initial function is zero, it grows as the FC calculation proceeds and finally becomes essentially exact at convergence. The same was true for all the quantities studied here, irrespective of the type of the initial wave function. For the helium atom, the cusp conditions including the electron–electron cusp were also examined with the FC wave function calculated before and shown to converge to the exact values. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

In this article, we present the multicore (mc) QM/MM method, a QM/MM method that can optimize the structure of chromophore aggregate in protein. A QM region is composed of the sum of the QM subregions that are small enough to apply practical electronic structure calculations. QM/MM energy gradient calculations are performed for each QM subregion. Several benchmark examinations were carried out to figure out availabilities and limitations. In the interregion distances of more than 3.5–4.0 Å, the mcQM/MM energy gradient is very close to that obtained by the ordinary QM/MM method in which all the QM subregions were treated together as a single QM region. In van der Waals complex, the error exponentially drops with the distance, while the error decreases slowly in a hydrogen bonding complex. On the other hand, the optimized structures were reproduced with reasonable accuracy in both cases. The computational efficiency is the best advantage in the mcQM/MM approach, especially when the QM region is significantly large and the QM method used is computationally demanding. With this approach, we could optimize the structures of a bacterial photosynthetic reaction center protein in the ground and excited states, which consists of more than 14,000 atoms. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [ABSTRACT FROM AUTHOR]

The ground and several electronic excited states of (3aS,7aS)-2-chalcogena-trans-hydrindans were calculated by the symmetry adapted cluster (SAC) and SAC-configuration interaction (SAC-CI) methods. Theoretical electronic excitation spectra and natural circular dichroism (CD) spectra were obtained for these compounds, and the calculated spectra showed good agreement with the experimental ones reported by Laur (Proceedings of the Third International Symposium on Organic Selenium and Tellurium compounds, Metz, France, 1979, pp. 219–299). For all the chalcogen compounds, the first singlet excited states are assigned to n-σ* and the other states are assigned to n-Rydberg in our calculations. It indicates that the spectra for the sulfide, selenide, and telluride are almost regarded as the analogues except for the red shifts of the band positions from the sulfide to the telluride. For the telluride, however, the experimental spectra have shapes that cannot be interpreted by the singlet excitations solely. Our calculations predict the triplet states that account for the spectral shapes, indicating importance of the spin-orbit interaction effects for the accurate reproduction of the experimental spectra of the telluride. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [ABSTRACT FROM AUTHOR]

Excited states of fluorescent proteins were studied using symmetry-adapted cluster-configuration interaction (SAC-CI) method. Protein-environmental effect on the excitation and fluorescence energies was investigated. In green fluorescent protein (GFP), the overall protein-environmental effect on the first excitation energy is not significant. However, glutamine (Glu) 94 and arginine (Arg96) have the red-shift contribution as reported in a previous study (Laino et al., Chem Phys 2004, 298, 17). The excited states of GFP active site (GFP-W22-Ser205-Glu222-Ser65) were also calculated. Such large-scale SAC-CI calculations were performed with an improved code containing a new algorithm for the perturbation selection. The SAC-CI results indicate that a charge-transfer state locates at 4.19 eV, which could be related to the channel of the photochemistry as indicated in a previous experimental study. We also studied the excitation and fluorescence energies of blue fluorescent protein, cyan fluorescent protein, and Y66F. The SAC-CI results are very close to the experimental ones. The protonation state of blue fluorescent protein was determined. Conformation of cyan fluorescent protein indicated by the present calculation agrees to the experimentally observed structure. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [ABSTRACT FROM AUTHOR]

Based on our previous study for the O2 binding of the Fe–Por complex, this study investigates the O2 binding mechanism in the Fe–porphyrin isomers, Fe–porphycene (FePc), and Fe–corrphycene (FeCor) complexes. By calculating the potential energy surface of the O2 binding, the present study explains the reason for the dramatic increase of O2 affinities observed in the FePc complex. In the case of FeCor–O2, the O2 binding process includes the intersystem crossing from a triplet to singlet state, as in the FePor–O2 complex. However, FePc–O2 uses only a singlet surface. This is because the ground state of the FePc complex in the deoxy state is a triplet state, while those of FePor and FeCor are a quintet state. Such difference originates from character of the SOMO. We estimated an equilibrium constant for the O2 binding that reasonably reproduced the trend observed in the experiments. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1363–1372, 2006 [ABSTRACT FROM AUTHOR]

Electronic mechanism of the reversible O2 binding by heme was studied by using Density Functional Theory calculations. The ground state of oxyheme was calculated to be open singlet state [Fe(S =1/2) + O2(S = 1/2)]. The potential energy surface for singlet state is associative, while that for triplet state is dissociative. Because the ground state of the O2+ deoxyheme system is triplet in the dissociation limit [Fe(S = 2) + O2(S = 1)], the O2 binding process requires relativistic spin-orbit interaction to accomplish the intersystem crossing from triplet to singlet states. Owing to the singlet-triplet crossing, the activation energies for both O2 binding and dissociation become moderate, and hence reversible. We also found that the deviation of the Fe atom from the porphyrin plane is also important reaction coordinate for O2 binding. The potential surface is associative/dissociative when the Fe atom locates in-plane/out-of-plane. © 2006 Wiley Periodicals, Inc. J Comput Chem 4: 426–433, 2006 [ABSTRACT FROM AUTHOR]

A correction to the article “Electronic Transitions in Conformationally Controlled Tetrasilanes with a Wide Range of SiSiSiSi Dihedral Angles" is presented.