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A step-by-step theoretical protocol based on the density functional theory (DFT) and time-dependent DFT (TD-DFT) has been performed to study a Ruthenium polypyridyl complex named cis-dithiocyanatobis-(4,4′-dicarboxy-2,2′-bipyridine) ruthenium(II) (N3) sensitized TiO 2 solar cell including dye excitations and electronic injection. Three binding structures of N3 anchored to a TiO 2 nanoparticle (TiO 2 ) 38 have been adopted. The electronic structures and optical properties of N3 dye in gas phase, in solutions (with the explicit and implicit solvent models), and interfaced with TiO 2 have been calculated. The hybrid DFT exchange-correlation (XC) functional B3LYP and PBE0, the newly-modified PBE0 functional PBE0-1/3, and the long-range corrected DFT (LRC-DFT) XC functional Cam-B3LYP have been applied. It is found that both the DFT XC functionals and molecular environments play a crucial role on molecular properties, which affect both the spectral lineshapes and peak positions. Coupled with PCM model, TD-PBE0-1/3 produces the best result compared with the experimental spectrum of N3 in CH 2 Cl 2 , TD-B3LYP slightly underestimates the excitation energies, and TD-Cam-B3LYP overestimates the excitation energies of 0.4–0.5 eV. As the solvent polarity increases, the electronic absorption spectra of N3 dye blue shift. The absorption manners of N3 anchored to (TiO 2 ) 38 affect the electronic excitations, leading to different electronic injection pathways. Two of three anchoring manners favor the interfacial electronic transfer. In the end, three possible electronic injection pathways from the different parts of the excited dye to TiO 2 nanoparticle have been suggested, indicating the different timescales of electron injections. [ABSTRACT FROM AUTHOR]

Nowadays, it is an attractive strategy to promote the efficiency of photocatalytic reactions by introducing the heterojunctions. Bismuth vanadate (BiVO4), one of the promising non-titania-based visible light-driven semiconductor photocatalysts, possesses three different crystal phases which can transform from one phase to another under appropriate conditions. The heterophase junction built by the monoclinic scheelite (s-m) and tetragonal zircon (z-t) phase BiVO4 has been demonstrated to have high photocatalytic activity than the single-phase BiVO4. Here we presented a step-by-step protocol based on the first-principles density functional theory calculations to explore the origin of high photocatalytic activity existed in BiVO4 heterojunction. The mixed-phase geometrical structures, density of states, electrostatic potential, electron localization function and band offsets of optimal interface have been calculated. For the heterojunction, the calculated valence band maximum and conduction band minimum of z-t BiVO4 are 0.29 and 0.32 eV above those of s-m BiVO4, respectively, indicating that the presence of interface in monoclinic/tetragonal heterophase provides a spatial condition for charge carrier separation and promotes the separation of photoinduced electron–hole pairs. Further calculations reveal that the direction of electron migration across the phase boundary is from z-t to s-m, consistent with the experimental observation. [ABSTRACT FROM AUTHOR]

In this review, we summarize the computationally efficient time-dependent approaches to calculating the vibronic spectra including one-photon/two-photon absorption (OPA/TPA), emission, circular dichroism (CD), and resonance Raman/hyper-Raman scattering (RRS/RHRS) spectra with inclusion of the mode-mixing, Frank-Condon (FC) and Herzberg-Teller (HT) effects. At first, a unified dependency of spectral differential cross sections (SDCSs) on a generalized linear polarizability is derived in view of the relationship between SDCSs and the linear or nonlinear polarizabilities. Then, the Green's function technique is adopted to calculate the polarizability to avoid the tedious summation over the large number of vibrational states. To demonstrate the computational accuracy and efficiency, we apply the generalized time-dependent approaches to calculate the OPA(E)/TPA, RRS, and RHRS spectra of a series of radicals and organic molecules. The computational accuracy is demonstrated by a close comparison between the simulated spectra and the available experimental data. In the spectral calculations, we apply our recently developed analytical energy-derivative approaches for the excited states within the framework of time-dependent density functional theory (TDDFT) to calculate the electronic-structure parameters which enter the expressions of SDCSs, such as the excited-state geometries, energy gradient, harmonic vibrational frequencies, the geometrical derivatives of transition dipole moments, and so forth. It is found that the integrated approach which combines the time-dependent approach to SDCSs with the analytical energy-derivative approaches for TDDFT excited-state structure parameters breaks the bottlenecks of vibronic spectroscopy calculation down. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory and time-dependent density functional theory with hybrid functional B3LYP are employed to investigate several physical and chemical properties of N-methyle-3,4-fulleropyrrolidine (NMFP), including geometry, electron population, infrared (IR), Raman and electronic absorption spectra. The analysis of the natural bond orbital (NBO) suggests that there are about 0.16 electrons transferred from the moiety –C3NH7 of NMFP to fullerene cage. The strongest IR and Raman spectra are from different modes with frequencies of 2955 and 1490cm−1, respectively. The calculated isotropic polarizability, polarizability anisotropy invariant and hyperpolarizability are 521.6, 65.3 and −68 (a.u.), respectively. The calculated electronic absorption spectra agree well with the experimental measurement. The solvent cyclohexane did not significantly affect the overall spectral shape but the absorption intensity and low-energy-band locations. The first absorption band in visible region comes from transitions, and the bands near 437 and 451 nm are both related to the ligand-to-fullerene charge transfer processes. The second absorption band in near-UV region is dominated by typical transitions. [Copyright &y& Elsevier]

In the modeling of spin‐crossing reactions, it has become popular to directly explore the spin‐adiabatic surfaces. Specifically, through constructing spin‐adiabatic states from a two‐state Hamiltonian (with spin‐orbit coupling matrix elements) at each geometry, one can readily employ advanced geometry optimization algorithms to acquire a "transition state" structure, where the spin crossing occurs. In this work, we report the implementation of a fully‐variational spin‐adiabatic approach based on Kohn‐Sham density functional theory spin states (sharing the same set of molecular orbitals) and the Breit‐Pauli one‐electron spin‐orbit operator. For three model spin‐crossing reactions (predissociation of N2O, singlet‐triplet conversion in CH2, and CO addition to Fe(CO)4), the spin‐crossing points were obtained. Our results also indicated the Breit‐Pauli one‐electron spin‐orbit coupling can vary significantly along the reaction pathway on the spin‐adiabatic energy surface. On the other hand, due to the restriction that low‐spin and high‐spin states share the same set of molecular orbitals, the acquired spin‐adiabatic energy surface shows a cusp (ie, a first‐order discontinuity) at the crossing point, which prevents the use of standard geometry optimization algorithms to pinpoint the crossing point. An extension with this restriction removed is being developed to achieve the smoothness of spin‐adiabatic surfaces. [ABSTRACT FROM AUTHOR]

Stepwise ring closing processes of platinum(II) alkynyl arkynyl bridged DTEs (OO→OC→CC) were studied theoretically with density functional theory method in this work for better understanding the Pt(II) alkynyl coordination effect on the photophysical and photochemical properties of dithienylethene (DTE). It is observed that the absorption spectrum of OO complex is red-shifted compared with that of ring-opened DTE monomer because of the decreased HOMO-LUMO gap energy. The first S 0 →S 1 absorption of OC is red shifted than that of OO and is blue shifted than that of CC complex because of the increased conjugation of the ring-closed DTE moiety. In addition, potential energy surface (PSE) studies show that the energy barrier for the ring-closing process in the ground state of Pt(II) complex is smaller than that of the isolated DTE monomer and the isomerization process is changed from endothermic to exothermic reaction. Moreover, the energy barrier for the first ring-closing process is a little larger than the second ring-closing process involved in the DTE moieties. More important, similar with that in the DTE monomers, the ring closing processes in the ionic and triplet states of Pt(II) complexes is easier than that in the neutral case. [ABSTRACT FROM AUTHOR]