This chapter introduces the Hubbard model and its applicability as a corrective tool for accurate modeling of the electronic properties of various classes of systems. The attainment of a correct description of electronic structure is critical for predicting further electronic-related properties, including intermolecular interactions and formation energies. The chapter begins with an introduction to the formulation of density functional theory (DFT) functionals, while addressing the origin of bandgap problem with correlated materials. Then, the corrective approaches proposed to solve the DFT bandgap problem are reviewed, while comparing them in terms of accuracy and computational cost. The Hubbard model will then offer a simple approach to correctly describe the behavior of highly correlated materials, known as the Mott insulators. Based on Hubbard model, DFT+U scheme is built, which is computationally convenient for accurate calculations of electronic structures. Later in this chapter, the computational and semiempirical methods of optimizing the value of the Coulomb interaction potential (U) are discussed, while evaluating the conditions under which it can be most predictive. The chapter focuses on highlighting the use of U to correct the description of the physical properties, by reviewing the results of case studies presented in literature for various classes of materials.
A holistic analysis of adsorption energies, charge transfer, and structural changes has been employed to highlight the variations in adsorption mechanisms upon changing the surface type and the adsorption site.
Organic–inorganic
hybrid perovskite compounds are currently
the archetypal materials for high performance photovoltaic (PV) and
optoelectronic devices. However, the remaining bottlenecks preventing
their large-scale production are their environmental/thermal instability
and lead toxicity. Herein, we demonstrate a novel approach to synthesize
single-phase electrospun Cs2SnI
x
Cl6–x
double perovskites with
varying halide content (I, Cl, or mixed I/Cl) as active materials
for potential application in perovskite solar cells (PSCs). The X-ray
photoelectron spectroscopy and Raman spectroscopy analyses indicated
the in situ formation of graphene oxide (GO) during
the annealing process. The GO layer was found to enhance the optical
properties and thermal stability of the fabricated perovskites even
at high Cl content. Moreover, the presence of GO as an insulating
layer significantly decreases the bandgap energy of the resulting
perovskites. The perovskites with a mix iodide and chloride ions showed
significantly improved optical properties with higher photoluminescence
(PL) intensity than that of pure chloride or iodide counterparts.
Moreover, the compound with low chloride content showed superior thermal
stability to those reported in the literature. Therefore, the application
of the electrospinning technique is a useful strategy to in
situ incorporate GO in lead-free perovskite matrix for potential
photovoltaic and optoelectronic applications.
A comprehensive analysis of low coverage CO adsorption on Ni and Cu low-index miller surfaces – (100), (110), and (111) – over all the possible adsorption sites is presented.
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