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Enhanced Moisture Stability of Cesium Lead Iodide Perovskite Solar Cells- A First-Principles Molecular Dynamics Study
摘要： An understanding of the interaction of water with perovskite is crucial in improving the structural stability of the perovskite. Hence, in this study, the structural and electronic properties of γ-CsPbI3 (220) perovskite surface upon the adsorption of water molecules have been investigated based on density functional theory calculations. Also, we perform the first-principles ab initio molecular dynamics simulations (AIMD) to explore the structural stability of the γ-CsPbI3 (220) perovskite surface in the presence of water molecules, and the results are compared with the conventional cubic CH3NH3PbI3 (100) perovskite surface. The water molecules show stronger interactions with the (220) surface of γ-CsPbI3 than the (100) of CH3NH3PbI3. However, AIMD results demonstrate that the former is much more stable, and no trace of surface degradation has observed upon the adsorption of water molecules.
关键词： water adsorption,density functional theory,perovskite,ab initio molecular dynamics,structural stability
更新于2025-09-19 17:13:59
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Electrons and Phonons Cooperate in the Laser-Induced Desorption of CO from Pd(111)
摘要： Femtosecond laser induced desorption of CO from a CO-covered Pd(111) surface is investigated with ab initio molecular dynamics with electronic friction that incorporates effects due to the excited electronic and phononic systems, as well as out-of-phase coadsorbate interactions. Our simulations show evidence of an important electron-phonon synergy in promoting CO desorption that has largely been neglected in other similar systems. At the saturated coverage of 0.75 ML, effects due to CO-CO interadsorbate energy exchange are also important. Our dynamics simulations, in concert with site-specific desorption energy calculations, allow us to understand the large coverage dependence of the desorption yields observed in experiments.
关键词： electron-phonon synergy,Pd(111),desorption,femtosecond laser,CO,electronic friction,ab initio molecular dynamics
更新于2025-09-16 10:30:52
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A Theoretical Study on Laser Cooling Feasibility of Group IVA Hydrides XH (X = Si, Ge, Sn, and Pb): The Role of Electronic State Crossing
摘要： The feasibility of direct laser cooling of SiH, GeH, SnH, and PbH is investigated and assessed based upon ?rst principles. The internally contracted multi-reference con?guration interaction method with the Davidson correction is applied. Very good agreement is obtained between our computed spectroscopic constants and the available experimental data. We ?nd that the locations of crossing point between the B26? and A21 states have the tendency of moving downwards from CH to SnH relative to the bottom of the corresponding A21 potential, which precludes the laser cooling of GeH, SnH, and PbH. By including the spin-orbit coupling effects and on the basis of the A215/2 →X253/2 transition, we propose a feasible laser cooling scheme for SiH using three lasers with wavelengths varying from 400 to 500 nm, which features a very large vibrational branching ratio (0.9954) and a very short radiative lifetime (575 ns). Moreover, similar studies are extended to carbon monosul?de (CS) with a feasible laser cooling scheme proposed. The importance of electronic state crossing in molecular laser cooling is underscored, and our work suggests useful caveats to the choice of promising candidates for producing ultracold molecules.
关键词： spin-orbit coupling,group IVA hydrides,electronic state crossing,ab initio,laser cooling
更新于2025-09-16 10:30:52
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Structures and Properties of Higher-Degree Aggregates of Methylammonium Iodide toward Halide Perovskite Solar Cells
摘要： Organic–inorganic halide perovskite solar cells have been in the limelight in recent years due to their outstanding power conversion efficiency (PCE) and facile synthesis. Despite of the ever increasing PCE that astonishes the solar cell community, many fundamental structural and theoretical aspects remain elusive, which inhibit our understanding on this fascinating material. Methylammonium iodide (MAI) is one important precursor to fabricate the halide perovskite materials based on the prototypical CH3NH3PbI3. Some MAI might remain in the CH3NH3PbI3 layer, forming a MAI-rich layer that is considered strongly affecting the perovskite solar cell performance. Therefore it is helpful to take one step back to re-evaluate the structures of MAI that is overlooked in many perovskite solar cell studies. In this manuscript, we identify the alternative structures of MAI aggregates via the ab-initio calculations, including the monomeric, dimeric, trimeric, tetrameric, pentameric, hexameric, heptameric, octameric and decameric structures of MAI. These aggregate structures are proposed to act as a simplified, yet efficient model to represent the MAI-rich region in perovskite solar cells that are usually simulated using the computationally expensive slab model. We find that the aggregates of MAI are universally stabilized by the hydrogen bonds. We further evaluate these MAI aggregate structures via studying the interactions between the MAI aggregates and an experimentally-proven additive iodopentafluorobenzene (IPFB) as an example, and show that the iodine atoms in the MAI aggregates acting as potential charge traps could be passivated by the additive molecule. The present study provides an efficient modeling platform for the MAI-rich halide perovskite materials without high computational cost.
关键词： aggregates,perovskite solar cell,methylammonium iodide,ab initio
更新于2025-09-12 10:27:22
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Absorption spectra, ligand field parameters and g factors of Cr<sup>3+</sup> doped α-Al<sub>2</sub>O3 laser crystal: <i>ab initio </i>calculations
摘要： In this paper we present, in the unified frame, the results of the ab initio investigations of absorption spectra, ligand field parameters and g factors for three valence chromium doped α-Al2O3 crystal. Our calculations are based on a new methodology applied to a cluster [CrO6]9- embedded in an extended point charge field of host matrix ligands. After the differential functional theory (DFT) optimization of the doped crystal, a vibrational theoretical spectroscopic study based on infrared (IR) spectroscopy has been employed in order to confirm the stability of the optimized doped crystal structure. The ab initio energy calculation of the electronic states and corresponding wave functions of Cr3+ are documented from the complete active space self-consistent field (CASSCF). The improved energy states from the N-electron valence second order perturbation theory (NEVPT2), second order dynamic correlation dressed complete active space (DCD-CAS2), difference dedicate configuration interaction with three degrees of freedom (MRDDCI3) and spectroscopy-oriented configuration interactions (SORCI), were analyzed. Based on the ab initio ligand field theory (AILFT) procedure we extracted ligand field (LF) parameters and spin-orbit coupling constant which were used to recalculate the energy levels of the studied system. In addition, g factors for the ground state 4A2 of Cr3+ ion in corundum are calculated taking into account the full configuration interaction. The results obtained are discussed and comparisons with measured values from the literature show a reasonable agreement, which justifies and recommend this new route of investigation.
关键词： Ligand field,g factors,Optical absorption spectra,Al2O3:Cr3+,Ab initio calculations
更新于2025-09-12 10:27:22
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A computational study of the electronic structure and optical properties of the complex TeO<sub>2</sub>/TeO<sub>3</sub> oxides as advanced materials for nonlinear optics
摘要： Electronic structure of series of tellurium oxide crystals within the TeO2—TeO3 binary system is studied with generalized gradient approximation to DFT, hybrid DFT-HF method with the PBE0 and B3LYP exchange-correlation functionals and with quasiparticle G0W0 approach. Comparison with available experimental data revealed significant underestimation of the band gap values within DFT. The hybrid DFT-HF method leads to slightly overestimated values of the bandgap, and the best agreement with experimental data provides the “one-shot” G0W0 calculations starting from Kohn-Sham solutions. The electronic structure of tellurium oxides is discussed in details. It is found that the bandgap value decreases proportionally to fraction of tellurium atoms in octahedral coordination. This change is due to formation of gap states by 5s(Te) electrons which do not participate in Te(VI)–O bonding. Dielectric susceptibilities are calculated within Random Phase approximation for the series of tellurium oxides and high nonlinear properties of the compounds are predicted by empirical Miller’s rule.
关键词： Ab initio,DFT,tellurium oxides,GW,nonlinear optics,electronic structure
更新于2025-09-12 10:27:22
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Experimental and theoretical studies of CuInS2 thin films for photovoltaic applications
摘要： CuInS2 thin films were synthesized by spray pyrolysis. The films were characterized using X-ray diffraction, Raman spectroscopy, and spectrophotometer (UV–Vis). The structural studies reveal that CuInS2 thin films are of chalcopyrite phase. The complex dielectric constants (εr and εi), the refractive index (n), extinction coefficient (k), absorption coefficient (α), gap energy (Eg), and the optical conductivity (σ) were calculated. The obtained results are suitable for photovoltaic applications. To confirm our experimental results, a series of Ab initio calculations was performed. The generalized gradient approximation and the mBJ potential for the exchange–correlation potential have been used to calculate the band structure, density of states, charge density, and optical properties of CuInS2.
关键词： thin films,optical properties,CuInS2,Ab initio calculations,spray pyrolysis,photovoltaic applications
更新于2025-09-12 10:27:22
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<i>Ab initio</i> exact diagonalization simulation of the Nagaoka transition in quantum dots
摘要： Recent progress of quantum simulators provides insight into the fundamental problems of strongly correlated systems. To adequately assess the accuracy of these simulators, the precise modeling of the many-body physics, with accurate model parameters, is crucially important. In this paper, we employed an ab initio exact diagonalization framework to compute the correlated physics of a few electrons in artificial potentials. We apply this approach to a quantum-dot system and study the magnetism of the correlated electrons, obtaining good agreement with recent experimental measurements in a plaquette. Through control of dot potentials and separation, including geometric manipulation of tunneling, we examine the Nagaoka transition and determine the robustness of the ferromagnetic state. While the Nagaoka theorem considers only a single-band Hubbard model, in this work we perform extensive ab initio calculations that include realistic multiorbital conditions in which the level splitting is smaller than the interactions. This simulation complements the experiments and provides insight into the formation of ferromagnetism in correlated systems. More generally, our calculation sets the stage for further theoretical analysis of analog quantum simulators at a quantitative level.
关键词： Nagaoka transition,ab initio exact diagonalization,ferromagnetic state,quantum simulators,strongly correlated systems,quantum-dot system
更新于2025-09-11 14:15:04
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Oxidation Induced Polymerization of InP Surface and Implications for Optoelectronic Applications
摘要： InP is among the most studied materials for energy-conversion applications including optoelectronics and photoelectrochemical devices. One of the longstanding challenges with this material—and III-V semiconductors more generally—is to understand and control surface oxide formation, which critically impacts device functionality, performance and durability. We integrate advanced in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and ab initio simulations to reveal the mechanism of the oxidation process on InP(001) surface. By interpreting the APXPS results through direct ab initio spectroscopic calculations of surface models, and by comparing calculated and measured work functions, we provide an unbiased picture of the chemical evolution of the thermal oxide. At low temperatures (< 573 K), O2 exposure leads to predominant formation of crosslinked POx units dispersed with submonolayer thickness, which grow into an amorphous 2D film that is kinetically limited to the surface layer. Increased temperature (> 573 K) leads to the polymerization of POx units and the formation of a complex, inhomogeneous 3D network of surface oxide that is progressively indium rich and phosphorus poor towards the surface. Finally, accelerated phosphorus loss via a hitherto unreported coupled charge-transfer isomer transformation mechanism leads to the formation of a thick, amorphous In2O3-like oxide at 773 K with very different optoelectronic and hot carrier transportation properties. In addition to unraveling complex mechanisms of surface oxidation, our results suggest the possibility of deliberately tuning oxide composition by leveraging competition between thermodynamic and kinetic factors.
关键词： InP,APXPS,surface oxidation,ab initio simulations,photoelectrochemical devices,optoelectronics
更新于2025-09-11 14:15:04
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Effects of Gas-Phase Conditions and Particle Size on the Properties of Cu(111)-Supported Zn <sub/>y</sub> O <sub/>x</sub> Particles Revealed by Global Optimisation and Ab Initio Thermodynamics
摘要： The characterisation of the interaction between nano- or sub-nano- particles with a support nowadays increasingly relies on computational modelling by means of the density functional theory calculations. These provide valuable atomic-detail understanding of the structure and energetics of supported clusters, but it is still challenging to find (or design) structural models that are representative of real systems in terms of size, structure, and composition. In this study, we have applied an extensive and systematic approach combining global optimisation based on an evolutionary algorithm with atomistic ab initio thermodynamics for finding stable structures of a relevant material for catalytic methanol synthesis: Cu(111)-supported ZnyOx clusters. We identify the ZnO3 motif as the elementary building block of such clusters, on which we recently have investigated the full catalytic process for methanol synthesis. With the collection of global minima of Cu(111)-supported ZnyOx clusters resulting from this large-scale global optimisation effort, we assess the effect of size, gas-phase conditions, and support interactions on the phase diagrams, reactivity, and structural properties of the ZnyOx particles. We find moderate size-effects that are mostly related to the differences in stable Zn:O ratios of the identified global minima and to the formation of different sites in larger clusters. In contrast, large differences in the oxidation state of the clusters as defined by the gas-phase conditions significantly affect the geometry, electronic structure, and reactivity of the ZnyOx particles. This highlights the importance of thoroughly sampling structures with different stoichiometry and appropriately assessing their stability using a detailed thermodynamics analysis.
关键词： global optimisation,Cu(111)-supported ZnyOx clusters,ab initio thermodynamics,density functional theory,methanol synthesis
更新于2025-09-11 14:15:04