Irradiation on liquid water and ice by ultraviolet light in the range of 150–200 nm can create volatile OH radicals which react with other organic and inorganic molecules actively. However, the mechanism for OH radical formation in the condensed-phase water in this energy range is still unclear. To uncover this mechanism we studied the excited-state behaviors of ice using first-principles calculations based on many-body Green’s function theory. First, we showed that the long-wavelength optical absorption at the Urbach tail (190–300 nm) can be attributed to inherent hydroxide ions or transient structures formed in the autoionization process. Second, we revealed that creation of the OH radicals can be attributed to two mechanisms. Irradiation by the light at the Urbach tail excites an electron out of the hydroxide ion, leaving a neutral OH radical behind. By the light around 150 nm, OH radicals can be produced barrierlessly via direct water photolysis through concerted proton and electron transfer. Our results provide valuable insights into the excited-state dynamics of condensed-phase water, helping us understand in depth the photocatalytic reactions, radiation biology and chemistry.

The coupling of carbon nanodots (C-Dots) with graphitic carbon nitride (g-C3N4) has been demonstrated to boost the overall photocatalytic solar water splitting efficiency. However, the understanding on the role of the C-Dots and how the structure of C-Dots influences the photocatalytic reaction is still limited. In this work, we investigate the excited states of some C-Dot/g-C3N4 composites with the C-Dots containing different functional groups including –OH, –CHO and –COOH by first-principles many-body Green's function theory. It is found that the increase of efficiency can be ascribed to the high separation rate and the low recombination rate of the electron–hole pair benefiting from the emergence of the charge-transfer excited state between the C-Dots and g-C3N4. Functional groups on the C-Dots play a crucial role in determining the charge transfer direction, active sites for reduction reaction and oxidation reaction of water, and whether the reaction is a four-electron process or a two-electron/two-electron process. These results can provide guidance for the design and optimization of the C-Dots for heterojunction photocatalysts.

Using ab initio many-body Green’s Function theory, the electronic and optical properties of pure BAs, InAs as well as B- and/or In-doped GaAs supercells were studied. The results show that the calculated quasiparticle band gaps of BAs and InAs are in agreement with the experiments. The electronic and optical absorption properties of B- and/or In-doped GaAs are very sensitive to the lattice constant models used in the calculations, which can explain the controversies in previous theoretical and experimental works. Under the lattice constant condition based on the Vegard’s Law, the reduced band gap and the redshift of the first excited state E0 can be observed for InyGa1–yAs with In concentrations(atomic fractions) ranging from 0 to 15.625%, while the band gap increase and the blueshift of state E0 can be realized for BxGa1–xAs. However, an opposite trend can be found when the lattice constant is fixed to the experimental value, i.e., In doping leads to a band gap increase and a blueshift of the E0 state, while B doping results in a band gap decrease and a redshift of the E0 state. For BxGa1–x–yInyAs, the values of the band gap variation and the shift of state E0 are well located between the B and In mono-doping cases. It is worth mentioning that B doping does not introduce new impurity states in the band gap of GaAs or InyGa1–yAs.

Molecular-dynamics simulations were used to investigate the structures of hydrogen molecules formed within (5,5), (9,0) and (10,10) single-walled carbon nanotubes (SWNT). In the (5,5) and (9,0) SWNTs, H2 molecules preferably form linear lines and helical curves, showing the strong confinement of small-diameter SWNTs. The structure of H2 molecules in the (5,5) and (9,0) SWNTs is different, showing the dependence on the helicities of the SWNTs. The accumulation process of H2 molecules in the (10,10) SWNT is also presented, showing the formation of H2 molecules cylindrical shells.

Acene is a type of important organic semiconductor which has promising applications in various optoelectronic devices. The fission of a singlet to triplet in it has been expected to elevate the quantum efficiency of organic solar cells. However, the quantum efficiency is still very low and the fission process is still under debate. Controversies also exist on the energies of the singlet and triplet states in acene. Using the many-body Green's function theory, which includes the GW method and Bethe–Salpeter equation (BSE), we compared the electronic excited states of several kinds of acene molecules (naphthalene to pentacene) at geometries optimized by different approaches. The energies of both the singlet and triplet depend strongly on the geometries of the molecules and their stacking. The non-negligible contribution from the resonant and anti-resonant transition coupling can cause large errors of the Tamm–Dancoff approximation, and the full BSE is required to get accurate results which are consistent with experiments. We found that accurate ionization energies and exciton energies can only be obtained when the geometries optimized by the Hartree–Fock approach are used. Singlet fission may be realized in isolated molecules, clusters, and surfaces, but it is hard in perfect pentacene crystals energetically. We provide a methodology for future research on acene-based solar cells and other optoelectronic devices.

The coupling of carbon nanodots (C-Dots) with graphitic carbon nitride (g-C3N4) has been demonstrated to boost the overall photocatalytic solar water splitting efficiency. However, the understanding on the role of the C-Dots and how the structure of C-Dots influences the photocatalytic reaction is still limited. In this work, we investigate the excited states of some C-Dot/g-C3N4 composites with the C-Dots containing different functional groups including –OH, –CHO and –COOH by first-principles many-body Green's function theory. It is found that the increase of efficiency can be ascribed to the high separation rate and the low recombination rate of the electron–hole pair benefiting from the emergence of the charge-transfer excited state between the C-Dots and g-C3N4. Functional groups on the C-Dots play a crucial role in determining the charge transfer direction, active sites for reduction reaction and oxidation reaction of water, and whether the reaction is a four-electron process or a two-electron/two-electron process. These results can provide guidance for the design and optimization of the C-Dots for heterojunction photocatalysts.