Chemical Physics最新文献

Calculation of nonlinear spectra of chromophore aggregates using response function theory when the number of contributing chromophores is large, and the level of excitation is high is extremely complicated. The main limitation is due to the exponential growth of computational time due to the aggregate size and number of excitations when considering an arbitrary excitation intensity. Non-perturbative calculation of spectra in this case becomes advantageous. We revisit our proposed model with exciton - exciton annihilation terms and apply it to large aggregates. We generalize the equations for both paulions and bosons with a parameter that allows smooth transition from one description to another. Intermediate statistics may also be valuable as molecular electronic excitations do not strictly obey either boson or paulion statistics. Specific approximations allow efficient calculation of pump-probe spectra for a large J aggregate.

An improved Wei potential energy function as a molecular potential model has not been widely reported probably due to its physical structure. In this study, the Feinberg–Horodecki (FH) equation is examined for the improved Wei energy potential function. To validate the calculations, the Feinberg–Horodecki equation is transformed into an energy equation by putting $c=1,$ and $P_n=E_n.$ Numerical results are generated for some molecules using the energy equation and the molecular spectroscopic constants for $\lambda =-0.1,0,$ and 0.1. The predicted results for the energy eigenvalues are compared with the experimental data for four halogen molecules and four gallium halides. The results revealed that the negative values of $\lambda$ do not produce values that align with the experimental data. It is also shown that the result obtained with $\lambda =0$ reproduces a better result for the improved Wei potential energy function than the result obtained with $\lambda =0.1.$

This study reports the structural, electronic, optical, phonon, thermodynamic and thermoelectric properties of ${\mathrm{AgYF}}_3$ (X=Mg, Sr) for photovoltaic and energy applications. We performed first principles calculations using full potential linearized augmented plane wave, FP-LAPW method implemented in Wien2k. The generalized gradient approximations of Perdew–Burke–Ernzerhof PBE-GGA, and PBE revised for solids, PBEsol, is employed for structural optimization of these lead free halide perovskites. The Birch–Murnaghan energy volume curve fitting comprehend the structural stability. The optimized lattice constant of ${\mathrm{AgMgF}}_3$ and ${\mathrm{AgSrF}}_3$ obtained with PBE-GGA(PBEsol) is 3.99(3.92) Å and 4.42(4.65) Å. The stability is further tested with the help of formation energy and positive phonon dispersion curves calculations. For the calculations of explicit electronic and optical properties, we also employed Tran–Blaha modified Beck–Johnson (TB-mBJ) and Strongly Constrained but Appropriately Normed, SCAN, exchange and correlations functionals. The electronic band gap of ${\mathrm{AgMgF}}_3$ computed with PBEsol, TB-mBJ and SCAN is 1.96 eV, 5.25 eV and 2.59 eV exhibiting M-$\Gamma$ indirect band gap. The band gap energy of ${\mathrm{AgSrF}}_3$ is 2.06 eV, 6.42 eV and 2.70 eV with PBEsol, TB-mBJ and SCAN. The indirect band gap nature of ${\mathrm{AgSrF}}_3$ is confirmed by PBEsol and TB-mBJ while it anticipated direct band gap behavior with meta-GGA SCAN. The different optical parameters like dielectric constant, optical conductivity, energy loss function, absorption, reflectivity and refractive index are calculated to assess optical activity of both perovskites. Comprehensive electronic and optical analysis advocates the utility of ${\mathrm{AgMgF}}_3$ and ${\mathrm{AgSrF}}_3$ for different applications is solar technology and optoelectronic devices.

The unique structural properties of two-dimensional materials make them promising for energy storage applications. This work theoretically predicts for the first time that Monolayer VOPO₄ (MNL VOPO₄), exfoliated from the delithiated phase of tetragonal LiVOPO₄, is stable at room temperature, exhibiting excellent thermodynamic and kinetic stability, thus making it a promising high-capacity anode material for sodium-ion batteries (SIBs). Compared to bulk VOPO₄, the monolayer structure significantly reduces the sodium ion migration energy barrier from 1.006 to 0.0795 eV, thereby markedly enhancing sodium ion migration kinetics. MNL VOPO₄ can adsorb up to 32 sodium ions, corresponding to a theoretical capacity of 634.88 mA h g⁻¹ and an energy density of 895.18 Wh kg⁻¹. Furthermore, the excellent structural stability of MNL VOPO₄ favors its cycling performance during charge and discharge processes. This work provides theoretical insights for better utilizing and developing multi-atomic phosphate compounds as electrode materials for secondary batteries.

The remarkable potential of double perovskite materials, characterized by lead-free, non-toxic attributes and robust dynamical stability, positions them as highly promising candidates for both thermoelectric and optoelectronic applications. In light of this, a comprehensive investigation is undertaken through density functional theory to thoroughly explore the optoelectronic and transport characteristics of Cs₂LiBi$X_6$ (X = Br, I) double perovskite materials. To ascertain dynamic stability, phonon dispersion band structures are computed, and the structural stability is evaluated through the tolerance factor. The resulting band structures reveal narrow band gaps of 3.45 eV and 1.79 eV for the Br and Indium-based DPs, respectively. These narrow band gaps hold significant importance for applications such as ultraviolet detectors and other optoelectronic devices that function in the visible and UV-light spectrum. Notably, absorption peaks of maximal intensity emerge at 5.1 eV (76 nm) and 4.0 eV (67 nm) for the Br and Indium-based double perovskites, respectively. Furthermore, a comprehensive analysis of thermoelectric behavior is conducted, encompassing the figure of merit, power factor, Seebeck coefficient, and the ratio of electrical to thermal conductivity across a temperature range of 50–800 K. The exceptionally low lattice vibration values, coupled with a substantial enhancement in the thermoelectric figure of merit (ZT), notably underscore their significance for advanced thermoelectric generator applications.

Gadolinium silicate, (Gd₂SiO₅) co-doped with Ce and Eu has been found to exhibit enhanced luminescence efficiency, which makes it a promising material for use in scintillators and phosphors. It has excellent scintillation properties such as high density and high Zeff. In this study, we used density functional theory (DFT) calculations within the Wien2k software to investigate the effect of Ce and Eu concentration and native defects on the electronic structure and optical properties of Ce and Eu co-doped Gd₂SiO₅. We utilized the DFT + U method to treat the localized 4f electrons of Ce and Eu. Our results indicate that the electronic structure and optical properties of Ce and Eu co-doped Gd₂SiO₅ are significantly affected by the concentration of the dopants and presence of native defects. We found that increasing the concentration of Ce and Eu dopants leads to a shift in the bandgap to lower energies, resulting in enhanced absorption and emission spectra. Moreover, our calculations reveal that presence of oxygen vacancies and Gd interstitials can induce new defect levels in the bandgap, which may affect the luminescence properties of the material. Our study provides valuable insights into the atomic-level mechanisms that govern the luminescence properties of Ce and Eu co-doped Gd₂SiO₅ which can aid in the design and optimization of luminescent materials for various applications.

Dye-sensitized solar cells (DSSCs) are cost-effective photovoltaic devices that convert solar energy into electricity using a dye sensitizer, TiO₂ photoanode, electrolyte, and counter electrode. This study investigates the impact of substituents on the performance of naphthoquinone-based dye sensitizers in DSSCs. We analyzed various naphthoquinone derivatives’ electronic structures and light absorption properties using DFT and TD-DFT. Our results demonstrate that electron-donating groups enhance DSSC performance by improving light absorption and electron injection. Specifically, naphthoquinone derivatives with methoxy (Dye-2) and methyl (Dye-3) groups showed superior properties. TD-DFT analysis revealed high molar extinction coefficients over a broad spectrum, making these dyes efficient at capturing sunlight. Additionally, these dyes effectively interact with TiO₂, which is crucial for photostability and photovoltaic performance. In conclusion, naphthoquinone derivatives with electron-donating groups significantly improve DSSC performance, with Dye-2 and Dye-3 being strong candidates for high-performance applications.

The unique properties of cesium compounds have garnered increasing attention, among which Cs₂Ti₆O₁₃ shows great potential for applications. This paper synthesized Cs₂Ti₆O₁₃(CTO-3) using a template-assisted solvothermal method with cesium carbonate as the cesium source and tetrabutyl titanate as the titanium source. Among them, F127 and hexadecylamine are used as template agents to modulate the surface morphology and hydrophilicity of the precursor. The cesium ion sieve H₂Ti₆O₁₃ (HTO-3) synthesized after hydrochloric acid pickling has a large specific surface area and good hydrophilicity. This structure is conducive to the ion exchange between Cs⁺ and H⁺, resulting in a fast adsorption rate. It is completed within 2 h, and the adsorption capacity reaches 360 mg/g, which is significantly greater than that of the traditional high-temperature solid-phase method. The adsorption process of Cs⁺ on HTO-3 is more consistent with the pseudo-second-order kinetic equation model, and the adsorption process is chemical adsorption. HTO-3 exhibited good selectivity and cycle stability. At the fifth time of the adsorption-resolution cycle, the adsorption capacity was 87.1 % of the first time.

The surface relaxations, surface stability, electronic structures, and equilibrium morphology of D5₂-La₂O₃ were analyzed by means of first-principles calculations. The stoichiometric surfaces of D5₂-La₂O₃ possess thermodynamic energies of the following order: (0 0 1) < (1 1 0) < (1 0 0). Changes in temperature and the partial pressure of oxygen were employed to determine the energy of the non-stoichiometric surfaces. The results indicated that the energies of the (ns-1La1O)-terminated (1 0 0) and (ns-1La)-terminated (0 0 1) surfaces increased with increasing oxygen partial pressures and decreased with temperatures, whereas the (ns-1O)-terminated (0 0 1) and (ns-1O)-terminated (1 0 0) surfaces exhibited the reverse rule. According to the calculated density of states, surface relaxations primarily impact the surface electronic structures. The Gibbs-Wulff model was used to forecast the equilibrium morphology of D5₂-La₂O₃, which followed in comparison with other’s experimental findings.