Charge, bond order and valence in the AB initio SCF theory
Abstract
An operator of atomic charge is introduced, the expectation values of which are Mulliken's gross atomic populations on the individual atoms. Suitable definitions of the bond order (multiplicity) index and of the valence number of an atom in a molecule are also proposed for the SCF LCAO MO method. (The results apply also in the extended Hückel method.)
References (6)
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Fourth International Congress in Quantum Chemistry, Uppsala
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Cited by (1917)
Computational investigations on the performance of transition metal carbide (MXene) for methylene blue dye adsorption and remediation from wastewater
2024, Materials Today CommunicationsMXenes are receiving a lot of attention as adsorbents for environmental contaminants, due to their distinct characteristics, and the adsorption abilities were toughly influenced by the surface terminal groups. In this research the adsorption ability of free-standing Ti3C2 for methylene blue (MB) dye as a major hazardous contaminant in the watery environment is investigated and compared with the O and OH terminated MXene counterparts using computational material tools. DFT simulations are carried out to explore the structural properties and electronic structures, thermodynamic stability, and adsorption behavior of MB on the considered MXenes surface. The Ti3C2 monolayer is observed to behave as superior adsorbent for MB with strong interaction characteristic which is typical for the chemisorption followed by the Ti3C2(OH)2 and Ti3C2O2 MXenes with hydrogen bonding (strong physisorption) and electrostatics attractions, respectively. Meanwhile the DFTB-MD simulation of MB/MXene in ambient conditions reveals a strong ability of Ti3C2 monolayer in MB adsorption by chemical bond formation between N/C atom of MB and surface Ti atom followed by hydrogen bond formation in MB/Ti3C2(OH)2 system. The superior adsorption behavior of free-standing Ti3C2 monolayer in aqueous solution, make this novel monolayer a promising adsorbent for MB adsorption and removal from watery contaminants. The present findings will be beneficial for the design of suitable nanoadsorbents for remediation of hazardous organic contaminants from wastewater.
Sr-centered monocyclic carbon ring Sr@C<inf>14</inf>: A new stable cluster
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Element partitioning and stabilization for impurities removal between liquid silicon and silicate melts: Ab initio insights into electronic structure
2024, Journal of Molecular LiquidsThe partitioning and stabilization of common impurity elements challenge the impurity removal process during slag refining for developing high-purity metals. The role of electronic properties remains indistinct in the stability of non-metallic, alkaline earth metal, and transition metal impurity clusters in silicon and silicate melts, impeding the advancement of separation medium and purification process. Herein, local structures of impurity atoms are explored through ab initio molecular dynamics, and notable configurations are [PSi4], [TiSi10], [MgSi12] in silicon melts and [PO4], [TiO5], [MgO5] in silicate melts. A novel partition model based on impurity coordination predicted the impurity atoms’ distribution behavior consistent with industrial experiments. Furthermore, this model proposes a critical parameter that evaluates impurity oxidation levels in coexisting systems and establishes a quantitative link between melt structures and distribution ratio, enabling precise predictions from two-phase ab initio calculations. Innovatively, the electronic structure analysis assessed element partitioning through bonding characteristics and interactions within impurity clusters via parameters: electron density distribution, partial density of states, electron localization function, and Mayer bond order. This yields a distinctive mapping relationship between impurity distribution ratio and stability, evidenced by quantitative associations with 12 key ab initio-derived descriptors through Pearson correlation analysis. This work unveils the electronic properties governing partitioning and endows modeling approach for distribution, driven by cluster structure analysis and ab initio calculations.
Effective decapsulation method for photovoltaic modules: Limonene-induced EVA controlled swelling under sonication and debonding mechanism analysis
2024, Journal of Cleaner ProductionWaste crystalline silicon (c-Si) solar cells are rich in metal resources. The detachment of ethylene-vinyl acetate (EVA) copolymer is a critical step in the recycling of end-of-life (EoL) c-Si photovoltaic (PV) modules, but a clean and high-efficiency adhesive removal method is absent. In this study, we presented a green solvent-based approach using limonene with ultrasound assistance for the efficient delamination of EVA from c-Si PV modules. By adjusting the concentration of limonene solution, the degree of swelling of EVA was effectively controlled, reducing the risk of battery damage caused by uneven swelling. The application of an ultrasonic physical field to the swelling system expedited the diffusion and penetration of the swelling agent between the EVA layers, while simultaneously supplying energy for the fracture of cross-linking bonds. Under the optimized laboratory-scale condition (70 °C, 0.5 h and 0.1 M limonene), complete separation of the glass and backsheet from the EVA bonding layer was achieved. The intact c-Si solar cells thus have the potential to be fully recovered in subsequent processes. FT-IR tests and density functional theory (DFT) simulations confirmed that under ultrasound conditions, limonene molecules selectively attacked crosslinking bridges and side chains of ethyl vinyl acetate in the EVA molecular chain. This induced the breakdown of the EVA crosslinked network structure, resulting in a reduction in adhesive strength and ultimately achieving interlayer separation in 20min. The findings of this study provide theoretical support and technical insights for the clean and efficient recycling of PV modules.
Theoretical insights into the extraction behaviors of neptunium(VI) and plutonium(IV) based on the structure of organophosphorus ligands
2024, Separation and Purification TechnologyOrganophosphorus ligands such as TBP, TiAP, and DMHMP have exhibited excellent performance in recovering actinides from spent fuel. In this work, the molecular geometries and properties of TBP, TiAP and DMHMP were investigated using density functional theory calculations. Furthermore, the extraction mechanism of ligands for actinides (Np(Ⅵ), Pu(Ⅳ)) was further elucidated by simulating the microstructures and extraction reactions of metal–ligand complexes. The results demonstrate that the complexation ability of the three ligands on actinide cations (NpO22+ and Pu4+) follows the order of DMHMP > TiAP > TBP. The electrostatic potential (ESP) analysis indicates that the nucleophilic ability of DMHMP is stronger than that of the other two ligands. The frontier molecular orbital analysis of the three ligands represents that DMHMP has the highest HOMO energy, suggesting that it has the strongest electron-donating capability and is more likely to bond with metal ions. The values of Wiberg bond indices (WBI) suggest that the M
O bonds in DMHMP complexes have more covalency. According to the QTAIM analysis, the interactions between actinide cations and the ligands are predominantly ionic in nature. The molecular orbital analysis of the complexes shows that the M(NO3)n·2DMHMP (M
NpO22+ and Pu4+) complexes are more stable, which is supported by thermodynamic energy analysis. This work has clarified the complexing properties of actinide cations with three ligands, shedding light on the extraction mechanisms of organophosphorus ligands for actinide cations. It is anticipated to lay the theoretical foundation for the efficient recovery of critical actinide elements in spent fuel reprocessing, which will also provide innovative approaches for the design and development of related separation processes.The effect of the chemical bonding environment changes in FeN<inf>X</inf>: Hydrocarbon adsorption by DFT
2024, Inorganic Chemistry CommunicationsHydrocarbons resulting from petrol, natural gas, and biomass penetrated industry and daily life because of energy consumption. Therefore, their adsorption mechanism needs to be detailed for reliable and inexpensive sensor, capture, and gas storage technology. These mechanisms of hydrocarbons (methane CH4, ethane (C2H6), ethylene (C2H4), and acetylene (C2H2) on FeNx(x=2,3,4) embedded graphene surfaces are analyzed. DFT-derived parameters were calculated via Quantum Espresso software using Grimme-D3 Van der Waals (VdW) correction. Our first findings show that the chemical bonding environment of the central Fe atom is compassionate upon carbon atom incorporation into porphyrin units. As more carbon atoms are exchanged with nitrogen atoms, the mean bond strengths between Fe and neighboring atoms increase based on crystal orbital Hamilton population (COHP), crystal orbital bond index (COBI), and Atoms in Molecules (AIM) Bader Topological Analysis. As opposed to that, more carbon atoms in porphyrin units make Cporp-CGrap interactions weakened and more ionic. The relationships between the adsorption components (adsorption energy, amount of the charge transfer, elevation between molecule and surface, and the variation of magnetic moments) are examined. The strong interaction occurs for C2H2 molecule on FeN2 and FeN3, and C2H4 on all sheets. It was also found that the variation in integrated quantities of COHP (ICOHP)/COBI (ICOBI) and AIM-Bader parameters are in line with the adsorption energy variations of all molecules.