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In this work, a set of density-functional tight-binding (DFTB) parameters for the Zr–Zr, Zr–O, Y–Y, Y–O, and Zr–Y interactions was developed for bulk and surface simulations of ZrO2 (zirconia), Y2O3 (yttria), and yttria-stabilized zirconia (YSZ) materials. The parameterization lays the ground work for realistic simulations of zirconia-, yttria-, and YSZ-based electrolytes in solid oxide fuel cells and YSZ-based catalysts on long timescales and relevant size scales. The parameterization was validated for the zirconia and yttria polymorphs observed under standard conditions based on density functional theory calculations and experimental data. Additionally, we performed DFTB-based molecular dynamics (MD) simulations to compute structural and vibrational properties of these materials. The results show that the parameters can give a qualitatively correct phase ordering of zirconia, where the tetragonal phase is more stable than the cubic phase at a lower temperature. The lattice parameters are only slightly overestimated by 0.05–0.1 Å (2% error), still within the typical accuracy of first-principles methods. Additionally, the MD results confirm that zirconia and yttria phases are stable against transformations under standard conditions. The parameterization also predicts that vibrational spectra are within the range of 100–1000 cm–1 for zirconia and 100–800 cm–1 for yttria, which is in good agreement with predictions both from full quantum mechanics and a recently developed classical force field. To further demonstrate the advantage of the developed DFTB parameters in terms of computational resources, we conducted DFTB/MD simulations of the YSZ4 and YS12 models containing approximately 750 atoms.

While the development of dye-sensitized solar cells (DSSCs) has been ongoing for more than 30 years, the currently obtained efficiency is unsatisfactory. However, the study of DSSC development has produced a fundamental understanding of cell performance and inspired other devices, such as perovskite cell solar cells. DSSCs consist of a dye-sensitized photoanode, a counter electrode, and a redox couple in the electrolyte system. Each of the components has an important role and cofunctions with each other to obtain a high power conversion efficiency. Various modifications to each DSSC component have been applied to improve their performance. Additionally, to generate improvements, the effort to reduce production costs has been crucial. The utilization of natural sources for DSSC components is a possible solution to this issue. The utilization of natural resources also aims to increase the value of the natural resource itself. In this review, the applications of various natural sources for DSSC components are described, as well as the modification efforts that have been made to enhance their performance. The discussion covers the utilization of natural dye for sensitizer dyes in liquid DSSC applications: (1) utilization of biopolymers for quasi-solid DSSC electrolytes, (2) green synthesis methods for photoanode semiconductors, and (3) development of natural carbon counter electrodes. The detailed factors that influence improvements in cell performance are also addressed., Dye sensitized solar cells; Natural resources; Biopolymer; Natural counter electrode; Green synthesis.

Potential energy curves (PECs) and energy profiles of atomic O attack on coronene as a model for graphene/graphitic surface and interstellar reaction surface have been computed at the unrestricted B3LYP/cc-pVDZ level of theory to elaborate on atomic O attack mechanism and chemisorption on coronene. The PECs were generated by scanning the O atom distance to the closest carbon atom on "top" and "bridge" positions in the coronene, while fully relaxed geometries in the triplet state were investigated to gain the energy profile. We found that the most favorable geometry as the final product was the chemically bound O on the "bridge" site in the singlet state with an interaction energy of –29.2 kcal/mol. We recommended a plausible mechanism of atomic O attack and chemisorption reaction on coronene or generally graphitic surface starting from the non-interacting O atom and coronene systems into the chemically bound O atom on coronene.

Density-functional tight-binding (DFTB) parameters are presented for the simulation of the bulk phases of zirconium. Electronic parameters were obtained using a band structure fitting strategy, while two-center repulsive potentials were created by particle swarm optimization. As objective functions for the repulsive potential fitting, we employed the Birch-Murnaghan equations of state for hexagonal close-packed (HCP), body-centered cubic (BCC) and ω phases of Zr from density-functional theory (DFT). When fractional atomic coordinates are not allowed to change in the generation of the equation-of-state curves, long-range repulsive DFTB potentials are able to almost perfectly reproduce equilibrium structures, relative DFT energies of the bulk phases, and bulk moduli. However, the same potentials lead to artifacts in the DFTB potential energy surfaces when atom positions in the unit cell are allowed to fully relax during the change of unit cell parameters. Conventional short-range repulsive DFTB potentials, while inferior in their ability to reproduce DFT bulk energetics, are able to correctly reproduce the qualitative shape of the DFT potential energy surfaces, including the location of global minima, and can therefore be considered more transferable.

In this work, the electronic and photocatalytic properties of non-metal-doped ZrTiO4 are computed using the DFT + U method. This method allows for calculations of the systems with strong correlation electronic effects like several metal oxides, which the standard DFT fails to give the correct predictions. Applying on-site Coulomb energy (U) correction to bulk pristine ZrTiO4 yields an orthorhombic unit cell lattice parameter a = 4.804 A, b = 5.509 A, and c = 5.041 A, which is in good agreement with the experiment. The calculated band gap energy ( E g ) for pristine ZrTiO4 with DFT + U is 3.60 eV, which is in excellent agreement with the experimental value of 3.65 eV. Substitutional doping is more likely to occur at the O site than at the Zr or Ti site in the X-doped ZrTiO4 model. F substitution at O atom and Si substitution at Ti or Zr atom are thermodynamically favorable with negative formation energy. Substitutional doping of S at the O site, Se at the Ti site, or S/Se at the Zr site in ZrTiO4 can enhance the photooxidation and photoreduction ability. These materials are expected to have good catalytic activity for water decomposition, CO2 reduction, and N2 fixation in the visible light region.

Potential energy curves (PECs) of atomic fluorine adsorption on coronene as a model for graphene or nanocarbon surfaces have been computed. The PECs were obtained by scanning the fluorine atom distance to one of the center carbon atoms of the coronene molecule as model system in a “top” position from 4.0 to1.0 A in intervals of 0.1 A using a variety of quantum chemical methods. Various density functional theory (DFT) functionals, such as B3LYP, PBE, PBE0, CAM-B3LYP, and LC-ωPBE; approximate DFT methods such as several levels of the density-functional tight-binding (DFTB) method, as well as ab initio wave function theory methods such as MP2, CCSD, CCSD(T), and G2MS extrapolations, were used to evaluate energies for B3LYP/cc-pVDZ PEC geometries. G2MS is an approximation to the highly accurate CCSD(T)/cc-pVTZ level of theory in our work. We found that fluorine is chemically adsorbed on coronene with a binding energy of 22.9 and 23.3 kcal/mol at the B3LYP/cc-pVDZ and G2MS levels of theory, respectively, and 1...

Halogen-substituted N-methyl-4-piperidone curcumin analog compounds were studied for their molecular structure, molecular vibration analysis, natural bond orbital, ultraviolet spectra, molecular reactivity analysis, and nonlinear optical properties. The molecules in interest were the (3E,5E)-3,5-dibenzylidene-1-methylpiperidin-4-one along with its substituted halogen (X = F- or Cl- or Br-) at the ortho, meta and para position in the phenyl ring. The calculated geometrical parameters at B3LYP/6–311++G(d,p) were in good agreement with the available experimental XRD data. Using the frequency calculations, the molecular vibrational modes have been analyzed. Meanwhile, the hyperconjugative stabilization energies have been calculated using NBO analysis to address the donor and acceptor in the hyperconjugation. The calculated UV spectra at TD-CAM-B3LYP/6–311++G(d,p) show strong absorption around 300 to 320 nm which corresponds to the absorption in the UV-A and UV-B region. From molecular electrostatic potential surface, C O moiety is one of the electronegative regions in the compounds where the C X moiety is the other electronegative region of the compounds. Fluoro-substituted compounds are the compounds with the most electronegativity while bromo-substituted compounds are the compounds with the least electronegativity. Calculations of average local ionization energy surfaces have been performed to obtain information related to the local reactivity of the molecules where the phenyl becomes less reactive after the substitution. The calculated first hyperpolarizability is 6 to 17 times larger than urea, the standard nonlinear optic material. These findings imply that all of the molecules considered have potential to be applied as active sunscreen material or nonlinear optic material.

We report the preliminary results of the development of density-functional tight-binding (DFTB) repulsive potentials for the Zr – O element pair. The repulsive potentials were created using a computer code based on the particle swarm optimization. The potentials were tested on a set of systems for high temperature phases of bulk ZrO2, namely cubic and tetragonal. The potential sets were primarily developed for simulation of zirconia phase transitions at elevated temperatures.