Electronic Energy Gap Research Articles

The interplay of excitonic delocalization and vibrational localization in optical lineshapes: A variational polaron approach.

The dynamics of molecular excitonic systems are complicated by a competition between electronic coupling (which drives delocalization) and vibrational-electronic (vibronic) interactions (which tend to encourage electronic localization). A particular challenge of molecular systems is that they typically possess a large number of independent vibrations, with frequencies often spanning the entire spectrum of relevant electronic energy gaps. Recent spectroscopic observations and numerical simulations on a water-soluble chlorophyll-binding protein (WSCP) reveal a transition between two regimes of vibronic behavior, a Redfield-like regime in which low-frequency vibrations respond to a delocalized excitonic state, and a Förster-like regime where high-frequency vibrations act as incoherent excitations on individual pigments. Although numerical simulations can reproduce these effects, there is a need for a simple, systematic theory that accurately describes the smooth transition between these two regimes in experimental spectra. Here we address this challenge by generalizing the variational polaron transform approach of [Bloemsma et al., Chem. Phys. 481, 250 (2016)] to include arbitrary bath densities for systems with or without symmetry. We benchmark this theory against both numerical matrix-diagonalization methods and experimental 77K fluorescence spectra for two WSCP variants, obtaining quite satisfactory agreement in both cases. We apply this theory to offer an explanation for the large loss in apparent electronic coupling in the WSCP Q57K mutant and to examine the likely impact of the interplay between excitonic delocalization and vibrational localization on vibrational sideband shapes and apparent coupling strengths in high-resolution optical spectra for chlorophyll-protein complexes such as WSCP.

Tuning the optical and photophysical characteristics of DR1 through mixing with JGB

A dye mixture of Disperse red1 (DR1) and Janus green B (JGB) was prepared with different concentrations of the two dyes. The optical properties were studied for the two dyes and their mixtures in terms of the absorbance spectra. The direct optical energy gap in addition to the refractive index, extinction coefficient, dielectric constant and optical conductivity were estimated to the two dyes and their mixtures. The experimental energy gap was found to be 2.234 and 1.666 eV for DR1 and JGB respectively, while the values of the energy gaps for the mixtures were found to be ranging between these two values. On the other hand, the refractive index was found to be changed in a systematic way by changing the contents of the dye mixture. The same behavior was also observed for the dielectric constant and optical conductivity. The emission of the two dyes and their mixtures was studied in terms of fluorescence spectra using excitation wavelength of 300 nm where a change in the fluorescence intensity was observed by changing the contents of the mixture. Finally, TD-DFT simulations were performed for the two dyes and their mixture to study the electron density, electrostatic potential, energy gap and optical absorption spectrum and found to be compatible with the experimental measurements.

Enhancing biphenylene sensitivity for BF3 detection via nitrogen doping: A DFT study

The detection and monitoring of toxic gases are critical components of environmental protection. Boron trifluoride (BF3), in particular, poses a significant threat to both the environment and human health due to its destructive properties. To address this challenge, the development of highly reactive and sensitive sensors for detecting and trapping BF3 is essential. This study explores the potential of pristine biphenylene (BP), boron-doped BP (B-BP), and nitrogen-doped BP (N-BP) as gas sensors for BF3 detection using density functional theory (DFT) calculations at the M062X/6–31 g(d,p) level of theory. We found that nitrogen doping significantly enhances the reactivity of BP toward BF3 originating from strong chemisorption with an adsorption energy of −9.38 kcal/mol. This is accompanied by a notable 19.96 % change in the electronic energy gap, making N-BP an exceptionally sensitive material for gas detection. The results will be supported by natural bond orbital analysis, providing a detailed electronic analysis of the sensing capabilities of N-BP. Our results suggest that n-type doping can be an effective strategy to enhance both the reactivity and sensitivity of carbon-based monolayers for detecting boron trifluoride.

Systematic Engineering of Near-Infrared Small Molecules Based on 4H-Cyclopenta[1,2-b:5,4-b']dithiophene Acceptors for Organic Solar Cells.

Nonfullerene acceptors (NFAs) have emerged as tremendous materials, efficiently advancing bulk-heterojunction organic solar cells (OSCs) technology. Unlike their fullerene counterparts, NFAs offer the unique advantage of finely tunable electronic energy levels and optical characteristics, which correspond to substantial enhancement in power conversion efficiency of OSCs. Herein, we have introduced a new series of near-infrared NFAs (AY1-AY8) to advance this technology further. Our research deeply investigates the structure-property relationship and thoroughly explores the optical, optoelectronics, photophysical, and photovoltaic characteristics of a synthetic reference molecule (R) and the modeled AY1-AY8 NFAs series. We performed advanced quantum chemical simulations using density functional theory (DFT) and time-dependent DFT methods. Additionally, we also estimated key geometric characteristics such as frontier molecular orbitals, hole-electron overlap, density of states, molecular electrostatic potential, molecular excitation and binding energies, transition density matrix, and reorganizational energy of electrons and holes and compared them with those of a synthetic reference molecule (R). Our findings show that all designed materials (AY1-AY8) exhibit red-shift absorption, improved electronic charge mobility, and low binding and excitation energies compared to R. Notably, these designed materials (AY1-AY8) display significantly narrower electronic energy gaps (E g 1.89-1.71 eV), indicating enhanced charge shifting from the highest occupied molecular orbital to lowest unoccupied molecular orbital and broadening of the absorption spectrum. Moreover, we also revealed a comprehensive study of the donor/acceptor complex of PTB7-Th/AY8 to understand charge shifting between donor and acceptor molecules. Therefore, we strongly recommend this designed (AY1-AY8) series to the experimentalists for the future development of highly efficient OSC devices.

Photo-Physical Characteristics of Janus Green B in Different Solvents and its Interaction Mechanism with Silver Nanoparticles.

This work explores the effects of solvent polarity on Janus Green B (JGB) photophysical properties. The Lippert-Mataga, Billot, and Ravi equations were utilized to calculate the singlet-state excited dipole moments (µe) and ground state dipole moments (µg) using absorption and fluorescence spectra analyses. The results showed an increase in the former, which is suggestive of electronic structural alterations upon excitation. Analysis of fluorescence quantum yield values revealed that JGB's environment had an impact on its emission characteristics; it was particularly sensitive to silver nanoparticles, suggesting possible interactions. While simulations of electron density, electrostatic potential, and energy gap (Eg) helped to understand the electronic structure of JGB, theoretical absorption spectra produced by Time Dependent Density Function Theory (TD-DFT) calculations offered insights into electronic transitions during absorption. To sum up, the present study contributes to our comprehension of the molecular behavior of JGB in various solvents by elucidating the intricate relationship among solvent polarity, molecular environment, and interactions with silver nanoparticles. Additionally, theoretical computations support the interpretation of experimental results.

Mobility inhibition of arsenic in the soil: the role of green synthesized silica nanoparticles

The studies showed the effectiveness of green-synthesized SiO2NPs in mitigating the toxicity of Arsenic. Density Functional Theory (DFT) is a computational method used to determine electronic structure, energy gap, and toxicity prediction. Experimentally, silicon nanoparticles of 0 (S0) and 100% v/v (S100) were applied to the surface of the soil. 150 mL of Arsenic trioxide was applied twice at a rate of 0 (As0) and 3.2 g/mL (As3.2) at an interval of three weeks. Green synthesized SiO2NPs possessed a higher chemical potential (µ) and electrophilicity index; consequently, charges could be transferred and easily polarized. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the green synthesized SiO2NPs enable them to donate electrons and complex with arsenic, reducing their bioavailability and toxicity. Evidence from the studies further showed that SiO2NPs had buffered the soil acidity and electric conductivity, posing a high binding site and reactivity with exchangeable cations and micronutrients due to their smaller energy gap. Furthermore, the catalytic activities of the soil enzymes dehydrogenase (DHA) and peroxidase (POD) were greatly increased, which enhanced the electrostatic interaction between the SiO2NPs and As.

Thermal, X-ray spectroscopy, morphological, density functional theory and molecular modeling studies on yttrium(III), germanium(IV), tungsten(VI), and silicon penicillinate antibiotic complexes

This manuscript elucidates the thermal stability analysis of four distinct penicillinate complexes, comprising yttrium(III), germanium(IV), tungsten(VI), and silicon, over a temperature ranging from 25 to 800°C. Thermal data revealed the high thermal stability nature of the decomposition steps. According to the spectroscopic measurements, the chemical formula of penicillinate complexes were [Y(Pin)2].Cl.6H2O complex (1), [Ge(Pin)2].2Cl.2H2O complex (2), [W(Pin)2].4Cl complex (3), and [Si(Pin)2].2Cl.2H2O complex (4). The powder XRD pattern revealed crystalline to polycrystalline natures. The synthesized penicillinate complexes were subjected to theoretical calculations utilizing density functional theory (DFT) calculations, employing the lanL2DZ/6-311G++ level of theory. The optimized geometry of each penicillinate complex was discerned, and a comprehensive evaluation of various properties, including the HOMO→LUMO electronic energy gap, molecular electrostatic potential map, and additional physical parameters, was conducted and validated against experimental findings. Molecular docking tool was used to explore the anticancer activity of the synthesized penicillinate complexes in comparison with penicillin potassium drug (Pin). For the computational investigation, two kinases — CSF1R (PDB ID: 7MFC) and MEK2 (PDB ID: 1S9I) associated with breast cancer progression and estrogen-dependent breast cancer were utilized. This comprehensive analysis provides a deeper understanding of the synthesized penicillinate complexes and their potential applications. KEY WORDS: Penicillinate complexes, TGA-DrTGA, TEM, XRD, DFT/TD-DFT, Molecular docking Bull. Chem. Soc. Ethiop. 2024, 38(4), 973-988. DOI: https://dx.doi.org/10.4314/bcse.v38i4.13

Local gate control of Mott metal-insulator transition in a 2D metal-organic framework

Electron-electron interactions in materials lead to exotic many-body quantum phenomena, including Mott metal-insulator transitions (MITs), magnetism, quantum spin liquids, and superconductivity. These phases depend on electronic band occupation and can be controlled via the chemical potential. Flat bands in two-dimensional (2D) and layered materials with a kagome lattice enhance electronic correlations. Although theoretically predicted, correlated-electron Mott insulating phases in monolayer 2D metal-organic frameworks (MOFs) with a kagome structure have not yet been realised experimentally. Here, we synthesise a 2D kagome MOF on a 2D insulator. Scanning tunnelling microscopy (STM) and spectroscopy reveal a MOF electronic energy gap of ∼200 meV, consistent with dynamical mean-field theory predictions of a Mott insulator. Combining template-induced (via work function variations of the substrate) and STM probe-induced gating, we locally tune the electron population of the MOF kagome bands and induce Mott MITs. These findings enable technologies based on electrostatic control of many-body quantum phases in 2D MOFs.

Electronic phase transformations and energy gap variations in uniaxial and biaxial strained monolayer VS[formula omitted] TMDs: A comprehensive DFT and beyond-DFT study

In the rapidly evolving field of 2D materials, transition metal dichalcogenides (TMDs) have emerged as compelling candidates for electronic applications. This study investigates the electronic structure of the H-phase monolayer VS2 belonging to TMD family and the influence of strain on its band structure through Density Functional Theory (DFT). We employ two different pseudopotential approximations and a suite of computational methods including DFT+U, GAUPBE, G0W0, and self-GW to provide a nuanced understanding of its electronic band structure. A highlight of the study is its focus on how both uniaxial and biaxial strains, ranging from -5% to +5%, affect the electronic properties of the H-phase monolayer VS2. Our comprehensive analysis reveals that these tensile strains significantly widen the energy gap, with uniaxial strains having a more pronounced effect than their biaxial counterparts. Additionally, we identify an intriguing phase transition from a semiconducting to a metallic state under compressive strains, this transition is attributed to both symmetry breaking and bond length variation in the uniaxial case, the bond length in biaxial. These key findings not only enrich our understanding of the intricate electronic behavior of monolayer VS2 under different strains but also pave the way for the design of innovative electronic devices using strain engineering.

Photoluminescence tuning of terbium tris-1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione complexes: Synthesis, spectroscopic, thermal and electrochemical analyses

The set of four ternary coordination compounds of terbium were prepared with diketone 1,1,1-trifluoro-5,5-dimethyl-2,4-hexanedione (TFDH) and four different neutral ligands (L) having formula [Tb(TFDH)3L]. Resulting compounds were characterized using different techniques including NUV absorption studies, photoluminescence (PL) spectroscopy, electrochemical and thermal analyses. PL spectra confirmed the green luminescence of synthesized complexes by exhibiting characteristic dominant 5D4 → 7F5 peak around 545 nm. Electronic and optical energy gap values lying at ∼3.5 eV reveals their potential to use in semiconductor materials. All the spectral results are in good agreement with each other and highlight their utility in lighting, biomedical imaging and sensors etc.

Electric-Tree Resistant Performance and Thermal Charge-Carrier Dissipation Mechanism of Voltage Stabilizer-Modified EPDM

In order to improve electric-tree resistant performance and dielectric breakdown strength of ethylene-propylene-diene misch-polymere (EPDM) material used for cable accessory reinforce insulation, the two specific aromatic ketone compounds—vinylphenylacetone (VPE) and 4-propylene oxyxy-2-hydroxydibenzenone (AOHBP) are employed as two paradigms of voltage stabilizer for chemical-graft modifications. Electric-tree resistances and insulation performances of modified EPDM materials and their charge trapping mechanism of thermoelectron inhibitions are studied by the accelerated electric-tree aging experiments, alternating current (AC) dielectric breakdown tests, surface potential trap-level analyses and first-principles calculations. Both the two species of voltage stabilizers are effective for promoting electric-tree inception voltage and dielectric breakdown strength, leading to a high extension of electric-tree morphology and smaller dimension of electric-trees growth, in which AOHBP is more significant. The two species of voltage stabilizers have been successfully grafted onto EPDM molecular-chains in thermal-chemistry crosslinking reactions of EPDM, introducing multiple shallow levels of charge traps, which reduces the energy released by trapping charge carriers and thus alleviates electric-tree aging of EPDM. The AOHBP and VPE represent a high electron affinity and a small electronic energy gap, which is competent of assimilating the kinetic energies of hot charge carriers whilst restricting Auger electronic excitation. Especially, the benzene group in voltage stabilizer renders shallow level charge traps with a larger carrier capture cross-section than deep traps and simultaneously possesses the high atomic vibration frequencies similar as electronic-transition energies, which results in effective dissipation on the kinetic energies of hot charge carriers. This mechanism dominates to increase electric-tree resistance and insulation strength of EPDM. The present study proves the important role of voltage stabilizers in improving insulation performance of EPDM material, and reveals the refrigeration mechanism on hot charge carriers for restricting electric-tree growth, which provides a significant strategy of chemical modifications for developing high-insulation cable accessory materials.

Theoretical investigation on the therapeutic applications of C2B and C2O as targeted drug delivery systems for hydroxyurea and 6-thioguanine in cancer treatment

This study employs density functional theory (DFT) calculations to examine the potential of C2B and C2O substrates as drug carrier frameworks for 6-thioguanine (6-TG) and hydroxyurea (HU) drugs, respectively. Utilizing the QuantumATK program, geometric, electronic, global reactivity, adsorption energy and optical properties of the interactions between C2B and C2O substrates and 6-TG and HU medications are estimated via DFT calculations. Consequently, the configuration and energies of adsorption, as well as other aspects of the interactions of 6-TG and HU with C2B and C2O substrates, are also computed, analyzed and discussed. According to the results, such as their electronic energy gaps, the structures with or without anticancer drugs exhibit semiconductor behavior. The interaction of the 6-TG and HU molecules with C2B and C2O causes a slight decrease or increase in the energy gap, except for the compound 6-TG/C2O, which behaves like a semi-metallic material with an energy gap of 0.679 eV. The adsorption energy of the 6-TG/C2B complex structure is notably greater than that of the other complex structures, with a value of −1.744 eV. In the field of drug delivery and biomedical research, the recovery time value suggest that C2B is more suitable as a carrier for the 6-TG medication compared to alternative structures.

Phosphorus-doped T-graphene nanocapsule toward O3 and SO2 gas sensing: a DFT and QTAIM analysis

Tetragonal graphene nano-capsule (TGC), a novel stable carbon allotrope of sp2 hybridization is designed and doped with phosphorus (P) to study the O3 and SO2 gas sensitivity via density functional theory calculation. Real frequencies verified the natural existence of both TGC and P-doped TGC (PTGC). Both TGC and PTGC suffer structural deformations due to interaction with O3 and SO2 gases. The amount of charge transfer from the adsorbent to the gas molecule is significantly greater for O3 adsorption than SO2 adsorption. The adsorption energies for TGC + O3 and PTGC + O3 complexes are − 3.46 and − 4.34 eV respectively, whereas for TGC + SO2 and PTGC + SO2 complexes the value decreased to − 0.29 and − 0.30 eV respectively. The dissociation of O3 is observed via interaction with PTGC. A significant variation in electronic energy gap and conductivity results from gas adsorption which can provide efficient electrical responses via gas adsorption. The blue/red shift in the optical response proved to be a way of detecting the types of adsorbed gases. The adsorption of O3 is exothermic and spontaneous whereas the adsorption of SO2 is endothermic and non-spontaneous. The negative change in entropy verifies the thermodynamic stability of all the complexes. QTAIM analysis reveals strong covalent or partial covalent interactions between absorbent and adsorbate. The significant variation in electrical and optical response with optimal adsorbent-gas interaction strength makes both TGC and PTGC promising candidates for O3 and SO2 sensing.

Insights into the Electronic, Optical, and Anti-Corrosion Properties of Two-Dimensional ZnO: First-Principles Study

The electronic, optical, and anticorrosion properties of planer ZnO crystal and quantum dots are explored using density functional theory calculations. The calculations for the finite ZnO quantum dots were performed in Gaussian 16 using the B3LYP/6-31g level of theory. The periodic calculations were carried out using VASP with the plane wave basis set and the PBE functional. The subsequent band structure calculations were performed using the hybrid B3LYP functional that shows accurate results and is also consistent with the finite calculations. The considered ZnO nanodots have planer hexagonal shapes with zigzag and armchair terminations. The binding energy calculations show that both structures are stable with negligible deformation at the edges. The ZnO nanodots are semiconductors with a moderate energy gap that decreases when increasing the size, making them potential materials for anticorrosion applications. The values of the electronic energy gaps of ZnO nanodots are confirmed by their UV-Vis spectra, with a wide optical energy gap for the small structures. Additionally, the calculated positive fraction of transferred electrons implies that electron transfer occurs from the inhibitor (ZnO) to the metal surface to passivate their vacant d-orbitals, and eventually prevent corrosion. The best anti-corrosion performance was observed in the periodic ZnO crystal with a suitable energy gap, electronegativity, and fraction of electron transfer. The effects of size and periodicity on the electronic and anticorrosion properties are also here investigated. The findings show that the anticorrosion properties were significantly enhanced by increasing the size of the quantum dot. Periodic ZnO crystals with an appropriate energy gap, electronegativity, and fraction of electron transfer exhibited the optimum anticorrosion performance. Thus, the preferable energy gap in addition to the most promising anticorrosion parameters imply that the monolayer ZnO is a potential candidate for coating and corrosion inhibitors.

Exploration of Solvent Effects, Structural and Spectroscopic Properties, Chemical Shifts, Bonding Nature, Reactive Sites and Molecular Docking Studies on 3-Chloro-2,6-Difluoropyridin-4-Amine as a Potent Antimicrobial Agent

This study delved into the electronic structure of Pyridine derivative 3-Chloro-2,6-difluoropyridin-4-amine (3C26D4A) using quantum-chemical computational calculations and employing the DFT/B3LYP/6-311++G(d,p) method and basis set. Spectroscopic, electronic, Mulliken population analysis and molecular electrostatic potential surface (MESP) calculations were carried out to gain deeper insights, shedding light on their bonding characteristics and reactive sites. The simulated electronic and frontier molecular orbitals (FMO) energy gaps of 3C26D4A in both polar (aniline, DMSO and methanol) and nonpolar (CCl4, chloroform, cyclohexane and toluene) confirm the stability and chemical reactivity. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gap of 3C26D4A in the gas phase is found to be 6.0214 eV and shows low reactivity and stability as compared to the solvent phase. In parallel, in silico molecular docking investigated their promise as antimicrobial agents by targeting key enzyme DNA gyrase. The obtained binding energy revealed a significant inhibitory potential docking score of -4.07 kcal/mol.

Direct determination of high-concentration As(III) by UV high-reference differential absorption spectroscopy for cleaner As(III) removal promotion via sulfurization

The current methods for determining high-concentration As(III) in the high-acid matrix from the copper smelting industry are complex, time-consuming, and costly. This limits effective modulation of sulfurizing agent dosage for As(III) removal via sulfurization, aggravating hazardous waste generation. Herein, a simple, rapid, and nondestructive UV high-reference differential absorption spectroscopy was developed to directly determine high-concentration As(III) in simulated high-acid wastewater. Time-dependent density functional theory calculations indicated that the spectral curve redshift with As(III) concentration increasing was related to the decrease of electron transition energies and energy gaps. When using high-reference solutions, the least redshift in the maximum absorption wavelength and the highest upper limit of linear fitting concentration could be obtained. Therefore, the piecewise quantitative linear model of differential absorbance and concentration was established under high-reference. The quantitative range of the model within 0.06–20.00 g/L As(III) with a mean relative error of < 5.0 % and standard recovery rates within 98.0 %-104.0 % indicated high accuracy. Additionally, the relative standard deviations of < 1.5 % (n = 5) revealed good precision. All results indicated the high feasibility of the developed method in alleviating linear deviation caused by redshift and absorption saturation. Furthermore, it has potential significance in saving sulfurizing agent dosage and reducing hazardous waste generation from the source, thereby facilitating a cleaner process for removing As(III) via sulfurization.

Spectroscopic, computational, cytotoxicity, and docking studies of 6-bromobenzimidazole as anti-breast cancer agent.

6-Bromobenzimidazole (6BBZ) has been calculated in this study utilizing the 6-311++G(d,p) basis set and the Becke-3-Lee-Yang-Parr density functional approaches. The basic frequencies and geometric optimization are known. FTIR, FT-Raman, and UV-Vis spectra of the substance are compared between its computed and observed values. The energy gap between highest occupied molecular orbital-lowest unoccupied molecular orbital and molecule electrostatic potentials has been represented by charge density distributions that may be associated with the biological response. Time-dependent density functional theory calculations in the gas phase and dimethyl sulfoxide were carried out to ascertain the electronic properties and energy gap values using the same basis set. Molecular orbital contributions are investigated using the overlap population, partial, and total densities of states. Natural bond analysis was found to have strong electron delocalization by means of π(C4-C9) → π*(C5-C6), LP (N1) → π*(C7-C8), and LP(Br12) → π*(C5-C6) interactions. The Fukui function and Mulliken analysis have been explored on the atomic charges of the molecule. The nuclear magnetic resonance chemical shifts for 1 H and 13 C have been computed using the gauge-independent atomic orbital technique. With the highest binding affinity (-6.2 kcal mol-1 ) against estrogen sulfotransferase receptor (PDB ID: 1AQU) and low IC50 value of 17.23 μg/mL, 6BBZ demonstrated potent action against the MCF-7 breast cancer cell line. Studies on the antibacterial activity and ADMET prediction of the molecule have also been carried out.

Insights into the optoelectronic behaviour of heteroatom doped diamond-shaped graphene quantum dots.

In this study we aim to manipulate the optoelectronic and photoluminescence properties of diamond-shaped graphene quantum dots (DSGQDs) in order to make them suitable for solar cells and photovoltaic devices. Using DFT and performing many-body effects studies, we investigate the impact of N, B, O, P and S heteroatom doping on DSGQDs in three different positions, namely the zigzag edge, the armchair corner and the surface, in order to identify the most appropriate and promising configurations. All the doped GQDs are found to be chemically stable making it possible to realize them experimentally. Additionally, the obtained results show that substitution with heteroatoms has a remarkable effect on the electronic energy gap, noticeably decreasing it. Doping also has a significant effect on the optical response by shifting the absorption peaks towards the visible energy range. The excitonic behaviour has revealed that these nanostructures are potential candidates for photovoltaic devices. One can deduce that doping DSGQDs with heteroatoms is useful and promising for the targeted applications.

Tuning electronic levels in photoactive hydroxylated titania nanosystems: combining the ligand dipole effect and quantum confinement.

Reducing the size of titania (TiO2) to the nanoscale promotes the photoactive anatase phase for use in a range of applications from industrial catalysis to environment remediation. The nanoscale dimensions of these systems affect the magnitude of the electronic energy gap by quantum confinement. Upon interaction with aqueous environments or water vapour, the surfaces of these systems will also be hydroxylated to some degree. In turn, this affects the electronic energy levels due to the cumulative electrostatic effect of the dipolar hydroxyl (-OH) ligands (i.e. the ligand dipole effect). Using accurate density functional calculations, we investigate the combined effects of quantum confinement and the hydration-induced ligand dipole effect on a set of realistic titania nanosystems over a wide range of hydroxylation. Our detailed investigation reveals that, contrary to previous models, the ligand dipole effect does not-linearly depend on the ligand coverage due to the formation of inter-ligand OH⋯OH hydrogen bonds. To account for the resulting effects, we propose a refined model, which describes the ligand dipole effect more accurately in our systems. We show that both hydroxylation (by the ligand dipole effect) and size (by quantum confinement) have significant but distinct impacts on the electronic energy levels in nanotitania. As an example, we discuss how variations in these effects can be used to tune the highest unoccupied energy level in nanotitania for enhancing the efficiency of the hydrogen evolution reaction. Overall, we show that any specific energy shift can be achieved by a range of different combinations of nanosystem size and degree of hydroxylation, thus providing options for energy-level tuning while also allowing consideration of practical constraints (e.g. synthetic limitations, operating conditions) for photochemical applications.

Theoretical study of physisorption of tosylate on AU10, AU15 and AU18 surfaces utilizing DFT approach

Charge transfer from organic nanomaterial to the coinage metal surfaces occur as a result to the physisorption physisorption phenomena. Physisorption plays a major role in many applications. A set of properties such as, molecular geometries, contour density maps, electrostatic potentials (ESPs), infrared spectra (IR), electronic states, HOMO and LUMO energies, Energy gaps (Eg), ionization potential (I.P), electron affinity (E.A),dipole moment, polarizabilities , average polarizability , symmetry and density of states by using Gaussian 09 software package algorithms were investigated at LANL2DZ, B3LYP and the ground state energy of (Au10-OTS) , (Au15) , (Au15-OTS), (Au18) and (Au18-OTS) , but the structure of (Au10) has been submitted at LANL2MB,B3LYP basis sets. The research study physisorption phenomena from the organic nanomaterial to sylate (OTS) to the coinage metal surface (gold surfaces), also the research concentrate if charge transfer procedure gets at the surface. Physisorption phenomena and charge transfer procedure that happen at the surface can be known throughout some properties such as the closed energy contour maps, electrostatic potentials, symmetry and density of states. Electronic states and energy gap property have been studied in this research to recognize importance of the geometrical structures in the electronic devices and the different electronic applications in different branch of knowledges. The research had the ionization potential and electron affinity credits to demonstrate if the geometrical structure will behave as a donor or an acceptor because the ionization energy demonstrate ability of the geometrical structure to donate the electrons in an interaction, but the electron affinity describes the capacity of the geometrical structure to accept electrons in an interaction.