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We report on accurate variational calculations of the Born–Oppenheimer potential for excited states of the hydrogen molecule with Π , Δ , and Φ symmetries. The obtained potential energy curves reach the relative precision of 10 − 9 or better along internuclear distances of 0.01–20 au. Calculations rely on the recursive evaluation of two-centre two-electron molecular integrals with exponential functions in arbitrary precision arithmetics. Our results for most of the states are the first-ever reported, and for the previously calculated states constitute an improvement by several orders of magnitude. [ABSTRACT FROM AUTHOR]

The performance of the extended multi-state (XMS)-complete active space second-order perturbation theory (CASPT2) method has been assessed for the benchmark of a truncated retinal model, the penta-2,4-dieniminium cation (PSB3). This benchmark presents a challenge for multireference electronic structure methods because the wave function character is changing considerably. The assessment comprises ground and excited state pathways of the isomerisation, including transition states and conical intersection (CI) points. It also includes circular paths centred around different CIs, and 2D potential energy scans located in the branching planes. In this work, we compare the performance of the previous formulations of CASPT2, the single-state and the multi-state, with the recently developed XMS-CASPT2. Besides, we have also tested two variants of internal contraction in XMS-CASPT2, namely, the single-state single reference (SS-SR) and multi-state multireference (MS-MR) schemes. In our study, we find that XMS-CASPT2 corrects the artefacts and discontinuities present in other CASPT2 variants. The investigation of a circular loop and 2D potential energy surfaces around the surface crossing point shows that XMS-CASPT2 exhibits a smooth topology at the CI with the correct degeneracy. It also agrees better with the reference method MRCISD+Q in regions of the potential energy surfaces further away from CIs. Another observation is the close agreement between the results from the SS-SR contraction scheme and the more demanding MS-MR scheme. [ABSTRACT FROM AUTHOR]

The ground-state geometries, electronic structures, spectra and photoelectric properties of two dyes (JA1 and JA2) used for dye-sensitised solar cells (DSSCs) have been investigated with density functional theory (DFT) and time-dependent density functional theory (TDDFT). For simulation of the realistic environment, we calculated the energy levels of molecular orbitals and absorption spectra in solvent, and the different electric fields have been considered. For interpreting the difference of photoelectric properties, we assessed the energy levels and energy gaps of frontier molecular orbitals, electron density, absorption, the total static first hyperpolarisability and driving force of electron injection. The relationship between structure and performance should be established. Furthermore, 24 dyes were designed on the basis of JA1 and JA2 to improve optical response and electron injection. The results of molecular modelling would provide the optional approach for improving performance of photoelectric materials. [ABSTRACT FROM AUTHOR]

In this work, the low-lying electronic singlet states of 9-methylhypoxanthine (9MHPX) were explored by the complete active space self-consistent-field (CASSCF) and complete active space second-order perturbation theory (CASPT2) calculations, and the conical intersections between the optically bright excited S1state and ground S0state were optimised by the two-root state-averaged SA-2-CASSCF approach. These studies indicate that four slightly different kinds of S1/S0conical intersections are identified computationally for 9MHPX, corresponding to four main internal conversion pathways, respectively, all of which are found to show the comparable timescales according to dynamics simulations. At the CASPT2 level, four brightππ* transitions of 9MHPX are calculated to locate at 4.47, 5.35, 5.97 and 6.30 eV, respectively, responsible for the available experimental absorption peaks of 9MHPX in the vapour phase (4.41, 5.19, 6.05 and 6.42 eV). Though one relatively weakππ* transition computed at 5.69 eV is not observed in the vapour phase, it is in accordance with the circular dichroism measurement of another hypoxanthine derivative deoxyinosine 5'-phosphate near 5.51 eV. [ABSTRACT FROM AUTHOR]

In this work, the excited state intermolecular potential energy surface of the Ar–CS2(V1B2) van der Waals complex was evaluated for the first time. The calculation of more than 4000 single-point interaction energies for the complex using an equation-of-motion coupled-cluster model with single and double substitutions level of theory with extended basis set involving bond functions has been performed. After fitting the interaction energies to analytical functions, the emission spectra of the Ar–CS2(V1B2) complex related to the different stationary points on the potential energy surface were calculated. It was seen that the intensity and the position of the emission spectra are dependent on the orientation of the Ar atom around the bent excited CS2and the distance between two components. The information about the structural parameters of the complex related to the global minimum was obtained under the pseudodiatomic approximation with assistance ofab initiopotential. The presented investigation could be useful for further theoretical and experimental studies of Ar–CS2(V1B2) complex. [ABSTRACT FROM AUTHOR]

The Fock-space multi-reference coupled cluster method is used for the geometry optimisation of the low-lying excited states of the molecules. Molecular geometries of the carbon monohydride cation (CH)+, water (H2O), ozone (O3) and formaldehyde (HCHO) in their low-lying excited states are optimised. Excited state gradients are calculated using finite field multi-reference coupled cluster method. We compare our results with other theoretical and/or experimental results, wherever available. [ABSTRACT FROM AUTHOR]

We present a time-dependent method for determining several approximate excited-state energies and wave functions using a vectorial approach to multidimensional supersymmetric quantum mechanics. First, a vectorial approach is used to generate the tensor sector two Hamiltonian, which is isospectral with the original scalar sector one Hamiltonian above the ground state of the sector one Hamiltonian. We construct a time-dependent Hamiltonian interpolating between the scalar sector one Hamiltonian and the tensor sector two Hamiltonian. Then, we can adiabatically switch from the ground state of the sector one Hamiltonian to the ground state of the sector two Hamiltonian by solving the time-dependent Schrödinger equation. In addition, by employing an initial wave packet orthogonal to that leading to the ground state of sector two, we also obtain the first-excited state of sector two. Construction of the orthogonal sector one states is trivial due to the tensor nature of sector two. The ground and first-excited states of the sector two Hamiltonian can be used with the charge operator to obtain the first two excited state wave functions of the sector one Hamiltonian. Excellent computational results are obtained for two-dimensional nonseparable degenerate and nondegenerate systems. [ABSTRACT FROM AUTHOR]

The extended S1/S0 conical intersection seam for the photochemical 2s + 2s, 2s + 2a and 2a + 2a cycloadditions of two ethylene molecules has been documented using the methodology described by Sicilia et al. (J. Chem. Theory Comput. 4, 257 (2008)). Two additional critical points on this prototype crossing seam were found as a result, although both lie more than 100 kcal mol−1 above the rhomboidal crossing located previously, and are not minima in the intersection space. Using VB theory, the branching space conditions for the conical intersection can be derived analytically, in fair agreement with calculated CASSCF results. Woodward–Hoffmann symmetry forbidden and allowed reactions are associated with the same extended conical intersection seam in this case. [ABSTRACT FROM AUTHOR]

Earlier results for the 11-cis to all-trans isomerisation of the retinal chromophore after photoexcitation, studied using time-dependent density functional theory with the hybrid CAM-B3LYP functional, are compared with new results using other long-range corrected DFT functionals. The TDDFT S0 and S1 minimum energy paths have been compared with the approximate coupled-cluster method RI-CC2. All calculations were consistent in producing an additional avoided crossing minimum on the S 1 minimum energy path lying approximately halfway between the 11-cis and all-trans S1 minima. In this minimum on the S1 potential energy surface, the retinal chromophore has inverted bond order in its carbon chain and lower energy than it has in both the 11-cis and all-trans S1 minima. [ABSTRACT FROM AUTHOR]

Peroxides are ubiquitous in the atmosphere and their photochemistry at ice surfaces is important. Here the primary steps following photoexcitation of methyl hydroperoxide (MHP) on ice particles are investigated using the MNDO method that describes semiempirically multiple electronic states and treats non-adiabatic dynamical transitions between them by surface hopping. Results are compared with the isolated MHP. Important findings are as follows. (1) Ice catalyzes the deactivation of MHP from the excited state to the ground state. (2) The deactivation process takes place on a femtosecond timescale and is followed by dissociation into fragments. (3) Recombination of fragments occurs to a small extent on ice, but not for the isolated peroxide. [ABSTRACT FROM AUTHOR]

Two novel fluorine-boron compounds were recently synthesised that exhibit high fluorescent efficiency, and can potentially function as electron transport materials (ETM) and blue emitters. To reveal the relationship between the properties and structures of these functional materials, theoretical analysis of the spectral properties and charge transport properties were systematically investigated with B3LYP and the 6-31G* basis set. The absorption spectra are simulated using time-dependent DFT methods (TD-DFT), whereas the emission spectra are simulated by optimising the excited state by single-excitation configuration interaction (CIS) and then carrying out vertical CI calculations using the TD-DFT method. The results are in good agreement with experiment. The results show that the studied compounds can act as excellent electronic transportation materials based not only on the smaller electronic reorganisation energy, but also on the larger electronic transfer integral. The phenomenon of the blue shift of absorption spectra with increasing solvent polarity is explained. The solvent effects on absorption and emission spectra were examined using the PCM and COMSO models, respectively. [ABSTRACT FROM AUTHOR]

Two conjugated organic dyes comprising the benzo[b]furan moieties as the electron donor and cyanoacetic acid moieties as the electron acceptor/anchoring groups have been investigated using a quantum chemical method. The molecular equilibrium geometries and ground state character were studied using density functional theory. Absorption spectra were obtained using time-dependent density functional theory and semiempirical ZINDO. The nature of absorption spectra was further studied using 2D and 3D real-space analysis; here, 2D real-space analysis showed electron-hole coherence, and 3D real-space analysis showed intramolecular charge transfer during photo-excitation. As important parameters, excited state oxidation potential and driving force energy were obtained to reveal the relationship between molecular structure and performance of two compounds. [ABSTRACT FROM AUTHOR]