Search results for "Density Functional Theory."
showing 10 items of 935 documents
Calculation of vibrationally resolved absorption and fluorescence spectra of the rylenes
2020
A generating function method was used to simulate the vibrationally resolved absorption and emission spectra of perylene, terrylene and quaterrylene. This method operates on the basis of adiabatic excitation energies and electronic ground and excited state vibrational frequencies. These parameters were calculated using density functional theory with the PBE0 functional for perylene and terrylene and with the BH-LYP functional for quaterrylene. The vertical excitation energies of the lower excited states were calculated using functionals with differing amounts of Hartree-Fock exchange. The optimal functional for each molecule was chosen by comparing these energies to literature excitation en…
Liquid–solid interfaces: structure and dynamics from spectroscopy and simulations
2014
Liquid–solid interfaces play an important role in a number of phenomena encountered in biological, chemical and physical processes. Surface-induced changes of the material properties are not only important for the solid support but also for the liquid itself. In particular, it is now well established that water at the interface is substantially different from bulk water, even in the proximity of apparently inert surfaces such as a simple metal. The complex chemistry at liquid–solid interfaces is typically fundamental to heterogeneous catalysis and electrochemistry, and has become especially topical in connection with the search for new materials for energy production. A quite remarkable exa…
Magnetic Properties of Quinoidal Oligothiophenes: More Than Good Candidates for Ambipolar Organic Semiconductors?
2006
A series of quinoidal oligothiophenes have been investigated by means of solid-state Fourier-transform (FT)-Raman and electron spin resonance (ESR) spectroscopies complemented with density functional theory calculations. FT-Raman spectra recorded as a function of temperature show that, upon laser irradiation, the molecules undergo a reversible structural evolution from a quinoid-type pattern at low temperature to an aromatic-type pattern at high temperature. Moreover, ESR spectra show that a portion of these compounds exists in a biradical state at room temperature. These seemingly disconnected findings and others, such as conformational isomerism, are consistently explained by the consider…
Au Adsorption on Regular and Defected Thin MgO(100) Films Supported by Mo
2007
Using density functional theory we studied systematically a Au atom adsorption on a Mo-supported regular and defected ultrathin MgO film with 1 to 5 ML thickness. On Mo(100) grown regular MgO Au prefers to adsorb at a hollow site instead of an O site found for single-crystal MgO. The metal support also enhances Au adsorption energy in agreement with the earlier theoretical results. Adsorption energy decreases with increasing film thickness being, however, even in the case of 5 ML thick MgO much higher than that on single-crystal MgO. The Bader analysis was performed to estimate the spatial distribution of charge in different cases. The results show charge transfer (0.7−0.8 e) to the Au atom…
Sub-gap defect density characterization of molybdenum oxide: An annealing study for solar cell applications
2020
AbstractThe application of molybdenum oxide in the photovoltaic field is gaining traction as this material can be deployed in doping-free heterojunction solar cells in the role of hole selective contact. For modeling-based optimization of such contact, knowledge of the molybdenum oxide defect density of states (DOS) is crucial. In this paper, we report a method to extract the defect density through nondestructive optical measures, including the contribution given by small polaron optical transitions. The presence of defects related to oxygen-vacancy and of polaron is supported by the results of our opto-electrical characterizations along with the evaluation of previous observations. As part…
A full-atom multiscale modelling for sodium chloride diffusion in anion exchange membranes
2021
Abstract A novel full-atom multiscale method, combining different computational approaches and aimed to describe diffusion of multiple ions in anion exchange membranes (AEM), is presented. The method is used to evaluate diffusion of chloride and sodium ions in polysulfone tetramethylammonium (PSU-TMA) membranes, with particular attention to the co-ion diffusion. The hydration of the PSU-TMA is computed as a function of the membrane ionic exchange capacity via Density Functional Theory (DFT) and used for carrying out molecular dynamics simulations (MD). An upgraded DFT-based approach is proposed to obtain the atoms’ charges used in the force field for the MD simulations. Three approaches hav…
Geometry, electronic structure, morphology, and photoluminescence emissions of BaW1-xMoxO4 (x = 0, 0.25, 0.50, 0.75, and 1) solid solutions: Theory a…
2019
Abstract The design of a solid solution with tunable electro-optical properties and multifunctionality is a promising strategy for developing novel materials. In this work, BaW1-xMoxO4 (x = 0, 0.25, 0.5, 0.75, and 1) solid solutions have been successfully prepared for the first time by a co-precipitation method. Their crystal structure and phase composition were determined by X-ray diffraction and Rietveld refinements. Fourier transform infrared and micro Raman spectroscopy in combination with field-emission scanning electron microscopy (FE-SEM) were used to describe the microstructures and chemical compositions of the synthesized materials. The influence of chemical composition on morpholo…
Diacetylene polymerization on a bulk insulator surface
2017
| openaire: EC/FP7/610446/EU//PAMS Molecular electronics has great potential to surpass known limitations in conventional silicon-based technologies. The development of molecular electronics devices requires reliable strategies for connecting functional molecules by wire-like structures. To this end, diacetylene polymerization has been discussed as a very promising approach for contacting single molecules with a conductive polymer chain. A major challenge for future device fabrication is transferring this method to bulk insulator surfaces, which are mandatory to decouple the electronic structure of the functional molecules from the support surface. Here, we provide experimental evidence for…
Understanding the optical and bonding properties of hybrid metal-halide (C5H16NP) PbX4 (X = Cl, Br, I) perovskite: A density-functional theory study
2021
Abstract Hybrid perovskites have demonstrated high stability and a promising optoelectronic performance for solar-cells. The quest over their functionalities beyond photo-voltaic applications is currently an important challenge. In this work, we have used density-functional theory to study hybrid perovskites. In particular, we have explored how atomic substitution could be used to design their optoelectronic properties. Under this approach, we have investigated the effect of changing the halogen atom (X = Cl, Br, I) on the structural, electronic, and optical properties of (C5H16NP) PbX4 hybrid perovskites. The electronic properties have been computed using hybrid functionals including the …
Small radius electron and hole polarons in PbX2 (X = F, Cl, Br) crystals: a computational study
2021
First-principles hybrid density functional theory (DFT) calculations were performed for small radius polarons – self-trapped electrons (STELs) and holes (STHs) in PbX2 (X = F, Cl, Br) crystals, widely used as parent materials for inorganic halide perovskites (CsPbX3) and scintillators. The atomic and electronic structures, spin and charge distributions and formation energies for both types of polarons were predicted for orthorhombic PbF2 and STELs for cubic PbF2. The STH structure was identified in a controversial case of PbCl2. We also confirmed and analyzed in detail experimentally suggested configurations for other cases. It is shown how, due to a delicate balance of ionic and covalent c…