Accuracy of Localized Resolution of the Identity in Periodic Hybrid Functional Calculations with Numerical Atomic Orbitals

We present an implementation of hybrid density functional approximations for periodic systems within a pseudopotential-based, numerical atomic orbital (NAO) framework. The two-electron Coulomb repulsion integrals (ERIs) are evaluated using the localized resolution-of-the-identity (LRI) approximation. The accuracy of the LRI approximation is benchmarked unambiguously against independent reference results obtained via a computational scheme whereby the ERIs are accurately evaluated by expanding the products of NAOs in terms of plane waves. An alternative strategy for constructing auxiliary basis sets is proposed, and its accuracy is assessed and compared to the previously used procedure. Finally, the reliability of our algorithm and implementation is benchmarked against other established implementations within different numerical frameworks in terms of the calculated band gap values of a set of semiconductors and insulators

Size Effects in the Interface Level Alignment of Dye-Sensitized TiO₂ Clusters

The efficiency of dye-sensitized solar cells (DSCs) depends critically on the electronic structure of the interfaces in the active region. We employ recently developed dispersion-inclusive density functional theory (DFT) and GW methods to study the electronic structure of TiO₂ clusters sensitized with catechol molecules. We show that the energy level alignment at the dye-TiO₂ interface is the result of an intricate interplay of quantum size effects and dynamic screening effects and that it may be manipulated by nanostructuring and functionalizing the TiO₂. We demonstrate that the energy difference between the catechol LUMO and the TiO₂ LUMO, which is associated with the injection loss in DSCs, may be reduced significantly by reducing the dimensions of nanostructured TiO₂ and by functionalizing the TiO₂ with wide-gap moieties, which contribute additional screening but do not interact strongly with the frontier orbitals of the TiO₂ and the dye. Precise control of the electronic structure may be achieved via “interface engineering” in functional nanostructures

Size Effects in the Interface Level Alignment of Dye-Sensitized TiO₂ Clusters

The efficiency of dye-sensitized solar cells (DSCs) depends critically on the electronic structure of the interfaces in the active region. We employ recently developed dispersion-inclusive density functional theory (DFT) and GW methods to study the electronic structure of TiO₂ clusters sensitized with catechol molecules. We show that the energy level alignment at the dye-TiO₂ interface is the result of an intricate interplay of quantum size effects and dynamic screening effects and that it may be manipulated by nanostructuring and functionalizing the TiO₂. We demonstrate that the energy difference between the catechol LUMO and the TiO₂ LUMO, which is associated with the injection loss in DSCs, may be reduced significantly by reducing the dimensions of nanostructured TiO₂ and by functionalizing the TiO₂ with wide-gap moieties, which contribute additional screening but do not interact strongly with the frontier orbitals of the TiO₂ and the dye. Precise control of the electronic structure may be achieved via “interface engineering” in functional nanostructures

Real-Time, Time-Dependent Density Functional Theory Study on Photoinduced Isomerizations of Azobenzene Under a Light Field

The trans to cis photoisomerization of azobenzene and its reverse (i.e., the cis to trans) processes are studied using real-time propagation time-dependent density functional theory combined with molecular dynamics for ions. We show that the wavelength of the applied laser may significantly affect the transition process. The simulations also show that the photon-excited electrons play essential roles in the isomerization processes, in which the hot electrons couple to phonon modes that drive the transitions

High-Resolution Model for Noncontact Atomic Force Microscopy with a Flexible Molecule on the Tip Apex

Experiments using noncontact atomic force microscopy (NC-AFM) with CO-molecule-functionalized tips have distinctly imaged chemical structures within conjugated molecules. Here we describe a detailed model based on an ab initio approach of the interaction force between the AFM tip and the sample molecule that yields atomic-scale images, which agree very well with the experimental images we considered. The key ingredient of our model is to explicitly include the effect on the image due to the tilt of the CO molecule at the tip apex resulting from the lateral force exerted by the sample. On the basis of this model, we specifically discuss the distortion seen in AFM images. As reported very recently, the distortion in AFM images originates from an intrinsic effect, namely, different extents of π-electron orbitals, as well as from an extrinsic effect, specifically CO tilt. We find that intrinsic distortion is scanning height dependent, attributing to the integrated electron density in the tip–sample overlapping region moving away from (the vertical projection of) the atom or bond positions. This intrinsic distortion is dominant in AFM images, although the atomic positions could be displaced even more by the extrinsic distortion due to CO tilt

Real-Time, Time-Dependent Density Functional Theory Study on Photoinduced Isomerizations of Azobenzene Under a Light Field

The trans to cis photoisomerization of azobenzene and its reverse (i.e., the cis to trans) processes are studied using real-time propagation time-dependent density functional theory combined with molecular dynamics for ions. We show that the wavelength of the applied laser may significantly affect the transition process. The simulations also show that the photon-excited electrons play essential roles in the isomerization processes, in which the hot electrons couple to phonon modes that drive the transitions

Altered Wnt signalling in the teenage suicide brain: focus on glycogen synthase kinase-3b and b-catenin

Glycogen synthase kinase (GSK)-3β and β-catenin are important components of the Wnt signalling pathway, which is involved in numerous physiological functions such as cognition, brain development and cell survival. Their abnormalities have been implicated in mood disorders and schizophrenia. Teenage suicide is a major public health concern; however, very little is known about its neurobiology. In order to examine if abnormalities of GSK-3β and β-catenin are associated with teenage suicide, we determined the gene and protein expression of GSK-3β and β-catenin in the prefrontal cortex (PFC) and hippocampus obtained from 24 teenage suicide victims and 24 normal control subjects. Protein expression was determined using Western blot with specific antibodies and gene expression (mRNA levels) was determined using the real-time polymerase chain reaction method. No significant change was observed in the GSK-3β protein levels either in the PFC or hippocampus of suicide victims compared to controls. However, protein levels of pGSK-3β-ser9 were significantly decreased in the PFC and hippocampus of suicide victims compared to normal controls. We also found that GSK-3β mRNA levels were significantly decreased in the PFC but not in the hippocampus of teenage suicide victims compared to controls. Mean protein and mRNA levels of β-catenin were significantly decreased in both the PFC and hippocampus of teenage suicide group compared to controls. The observation that there is a decrease in β-catenin and pGSK-3β-ser9 in the PFC and hippocampus of teenage suicide victims does indicate a disturbance in the Wnt signalling pathway in teenage suicide

Directional Growth of One-Dimensional CO₂ Chains on ZnO(101̅0)

Atomic insights into the interaction of CO2 with the mixed-terminated ZnO(101̅0) surface were achieved in detail by low-temperature scanning tunneling microscopy (LT-STM) together with density functional theory (DFT) calculations. The binding site and adsorption geometry were directly imaged by LT-STM, revealing that the CO2 molecules are chemisorbed and turned into surface carbonate species. The strong interaction of CO2 with the ZnO(101̅0) surface in turn activates the surface, i.e., reconstructs the local surface such that facilitates further CO2 bindings, leading to the formation of a one-dimensional assembly structure which grows along the [0001̅] direction. DFT simulations indicated that the superior agglomeration energies along ⟨0001̅⟩ directions as well as the CO2-induced surface reconstruction are responsible for the directional growth of the surface carbonate chains

Directional Growth of One-Dimensional CO₂ Chains on ZnO(101̅0)

Atomic insights into the interaction of CO2 with the mixed-terminated ZnO(101̅0) surface were achieved in detail by low-temperature scanning tunneling microscopy (LT-STM) together with density functional theory (DFT) calculations. The binding site and adsorption geometry were directly imaged by LT-STM, revealing that the CO2 molecules are chemisorbed and turned into surface carbonate species. The strong interaction of CO2 with the ZnO(101̅0) surface in turn activates the surface, i.e., reconstructs the local surface such that facilitates further CO2 bindings, leading to the formation of a one-dimensional assembly structure which grows along the [0001̅] direction. DFT simulations indicated that the superior agglomeration energies along ⟨0001̅⟩ directions as well as the CO2-induced surface reconstruction are responsible for the directional growth of the surface carbonate chains

Toward Low-Temperature Dehydrogenation Catalysis: Isophorone Adsorbed on Pd(111)

Adsorbate geometry and reaction dynamics play essential roles in catalytic processes at surfaces. Here we present a theoretical and experimental study for a model functional organic/metal interface: isophorone (C₉H₁₄O) adsorbed on the Pd(111) surface. Density functional theory calculations with the Perdew–Burke–Ernzerhoff (PBE) functional including van der Waals (vdW) interactions, in combination with infrared spectroscopy and temperature-programmed desorption (TPD) experiments, reveal the reaction pathway between the weakly chemisorbed reactant (C₉H₁₄O) and the strongly chemisorbed product (C₉H₁₀O), which occurs by the cleavage of four C–H bonds below 250 K. Analysis of the TPD spectrum is consistent with the relatively small magnitude of the activation barrier derived from PBE+vdW calculations, demonstrating the feasibility of low-temperature dehydrogenation