Understanding 2p core-level excitons of late transition metals by analysis of mixed-valence copper in a metal-organic framework

The L2,3-edge X-ray absorption spectra of late transition metals such as Cu, Ag, and Au exhibit absorption onsets lower in energy for higher oxidation states, which is at odds with the measured spectra of earlier transition metals. Time-dependent density functional theory calculations for Cu2+/Cu+ reveal a larger 2p core-exciton binding energy for Cu2+, overshadowing shifts in single-particle excitation energies with respect to Cu+. We explore this phenomenon in a Cu+ metal-organic framework with ∼12% Cu2+ defects and find that corrections with self-consistent excited-state total energy differences provide accurate XAS peak alignment.

Graphene quantum dots (GQD) and edge-functionalized GQDs as hole transport materials in perovskite solar cells for producing renewable energy: a DFT and TD-DFT study

This study investigated the potential suitability of graphene quantum dots (GQD) and certain edge-functionalized GQDs (GQD-3Xs) as hole transport materials (HTMs) in perovskite solar cells (PSCs). The criteria for appropriate HTMs were evaluated, including solubility, hole mobility, light harvesting efficiency (LHE), exciton binding energy (Eb), hole reorganization energy (λh), hole mobility, and HTM performance. It was found that several of the compounds had higher hole mobility than Spiro-OMeTAD, a commonly used HTM in PSCs. The open circuit voltage and fill factor of the suitable GQD and GQD-3Xs were found to be within appropriate ranges for HTM performance in MAPbI3 PSCs. GQD-COOH and GQD-COOCH3 were identified as the most suitable HTMs due to their high solubility, small λh, and appropriate performance.

Dissociative electron attachment to gold(I)-based compounds: 4,5-dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I)

With the use of proton-NMR and powder XRD (XRPD) studies, the suitability of specific Au-focused electron beam induced deposition (FEBID) precursors has been investigated with low electron energy, structure, excited states and resonances, structural crystal modifications, flexibility, and vaporization level. 4,5-Dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I) is a compound that is a uniquely designed precursor to meet the needs of focused electron beam-induced deposition at the nanostructure level, which proves its capability in creating high purity structures, and its growing importance in other AuIm_x and AuCl_nB (where x and n are the number of radicals, B = CH, CH₃, or Br) compounds in the radiation cancer therapy increases the efforts to design more suitable bonds in processes of SEM (scanning electron microscopy) deposition and in gas-phase studies. The investigation performed of its powder shape using the XRPD XPERT³ panalytical diffractometer based on CoK_α lines shows changes to its structure with change in temperature, level of vacuum, and light; the sensitivity of this compound makes it highly interesting in particular to the radiation research. Used in FEBID, though its smaller number of C, H, and O atoms has lower levels of C contamination in the structures and on the surface, it replaces these bonds with C-Cl and C-N bonds that have lower bond-breaking energy. However, it still needs an extra purification step in the deposition process, either H₂O, O₂, or H jets.

Increasing Charge Carrier Mobility through Modifications of Terminal Groups of Y6: A Theoretical Study

The applications of non-fullerene acceptor Y6 with a new type of A1-DA2D-A1 framework and its derivatives have increased the power conversion efficiency (PCE) of organic solar cells (OSCs) up to 19%. Researchers have made various modifications of the donor unit, central/terminal acceptor unit, and side alkyl chains of Y6 to study the influences on the photovoltaic properties of OSCs based on them. However, up to now, the effect of changes of terminal acceptor parts of Y6 on the photovoltaic properties is not very clear. In the present work, we have designed four new acceptors-Y6-NO2, Y6-IN, Y6-ERHD, and Y6-CAO-with different terminal groups, which possess diverse electron-withdrawing ability. Computed results show that with the enhanced electron-withdrawing ability of the terminal group, the fundamental gaps become lower; thus, the wavelengths of the main absorption peaks of UV-Vis spectra red-shifts and total oscillator strength increase. Simultaneously, the electron mobility of Y6-NO2, Y6-IN, and Y6-CAO is about six, four, and four times faster than that of Y6, respectively. Overall, Y6-NO2 could be a potential NFA because of its longer intramolecular charge-transfer distance, stronger dipole moment, higher averaged ESP, enhanced spectrum, and faster electron mobility. This work provides a guideline for the future research on modification of Y6.

Effects of Ge, Si, and B doping on the adsorption and detection properties of C60 fullerene towards methadone in gas and aqua phases: a DFT study

CONTEXT

Methadone can be abused and caused addictive and has various side effects. Therefore, the development of a fast and reliable diagnosis technique for its monitoring is essential. In this work, applications of C₆₀, GeC₅₉, SiC₅₉, and BC₅₉ fullerenes were investigated utilizing density functional theory (DFT) to find a suitable probe for methadone detection. The C₆₀ fullerene indicated weak adsorption energy for methadone sensing. Therefore, for the construction of the fullerene with good property for methadone adsorption and sensing, the GeC₅₉, SiC₅₉, and BC₅₉ fullerenes have been studied. The adsorption energy of GeC₅₉, SiC₅₉, and BC₅₉ in the most stable complexes were calculated at -2.08, -1.26, and -0.71 eV, respectively. Although GeC₅₉, SiC₅₉, and BC₅₉ all showed strong adsorption, only BC₅₉ present a high sensitivity for detection. Further, the BC₅₉ fullerene showing a proper short recovery time (about 1.11 × 10^-6 s for methadone desorption). Water as a solution is used to simulate the behavior of fullerenes in the body fluids, and results indicated that the selected pure and complex nanostructures are stable in water. The UV-vis spectrums indicated that the after adsorption of methadone on the BC₅₉ exhibits shift toward the lower wavelengths (blue shift). Therefore, our investigation indicated that the BC₅₉ fullerene is an excellent candidate for methadone detection.

METHODS

The interaction of methadone with pristine and doped C60 fullerenes surfaces was calculated using the density functional theory calculations. The GAMESS program and M06-2X method with a 6-31G(d) basis set were used for computations. Since the M06-2X method overestimates the LUMO-HOMO energy gaps (Eg) of carbon nanostructures, the HOMO and LUMO energies and Eg were investigated at the B3LYP/6-31G(d) level of theory using the optimization calculations. UV-vis spectra of excited species were obtained through the time-dependent density functional theory. To simulate the human biological fluid, the solvent phase was also evaluated in adsorption studies, and water was considered a liquid solvent.

Big Data in a Nano World: A Review on Computational, Data-Driven Design of Nanomaterials Structures, Properties, and Synthesis

The recent rise of computational, data-driven research has significant potential to accelerate materials discovery. Automated workflows and materials databases are being rapidly developed, contributing to high-throughput data of bulk materials that are growing in quantity and complexity, allowing for correlation between structural-chemical features and functional properties. In contrast, computational data-driven approaches are still relatively rare for nanomaterials discovery due to the rapid scaling of computational cost for finite systems. However, the distinct behaviors at the nanoscale as compared to the parent bulk materials and the vast tunability space with respect to dimensionality and morphology motivate the development of data sets for nanometric materials. In this review, we discuss the recent progress in data-driven research in two aspects: functional materials design and guided synthesis, including commonly used metrics and approaches for designing materials properties and predicting synthesis routes. More importantly, we discuss the distinct behaviors of materials as a result of nanosizing and the implications for data-driven research. Finally, we share our perspectives on future directions for extending the current data-driven research into the nano realm.

Micro-physical parameter dynamic evolution behaviour of a natural ester molecular chain under a changing electric field and its correlation mechanism with lightning impulse discharge: theoretical analysis

The lightning impulse breakdown properties of natural esters are very important for their further applications. This paper focuses on the discharge mechanism investigation of a natural ester insulating liquid under a lightning impulse electric field. Based on density functional theory (DFT), the configuration, electron structure, ionization and electron affinity process, excitation process and molecular orbital of natural ester molecules were calculated under different electric field strengths. A correlation mechanism between the micro-physical parameters of ester insulating liquid molecules and discharge was proposed. The molecular electrostatic potential was used to predict the active point of discharge. The results show that the molecular structure of triglycerides shows yield behaviour under electric field action. The electrons are redistributed in the direction of the source of the electric field. Among the four triglycerides, the ionization and electron affinity process, excitation process and molecular orbital of glycerol tripalmitate were least affected by the electric field. The microscopic properties of other triglycerides were significantly affected by the electric field. According to the electrostatic potential (ESP) result of natural ester molecules, it can be predicted in the experiment that the surface of H atoms of the triglyceride ester group easily forms electron traps to bind electrons, while the surface of an O atom at the ester of a triglyceride undergoes electron collisions resulting in an electrical discharge. The proportion of palmitic acid in natural esters could be increased or pure glycerol tripalmitate could be used as an insulating oil to solve the problem of the low lightning impulse breakdown voltage of natural esters.

Designing Potential Donor Materials Based on DRCN5T with Halogen Substitutions: A DFT/TDDFT Study

Experimental researchers have found that the organic solar cell (OSC) based on DRCN5T (an oligothiophene) possesses excellent power conversion efficiency (PCE) of 10.1%. However, to date, there have been few studies about halogenation of DRCN5T, and its effects on photovoltaic properties of halogenated DRCN5T are still not clear. In the present work, we first perform benchmark calculations and effectively reproduce experimental results. Then, eight halogenated DRCN5T molecules are designed and investigated theoretically by using density functional theory (DFT) and time-dependent DFT. The dipole moments, frontier molecular orbital energies, absorption spectra, exciton binding energy (E_b), singlet–triplet energy gap (ΔE_ST), and electrostatic potential (ESP) of these molecules, and the estimated open circuit voltages (V_OCs) of the OSCs with PC₇₁BM as acceptor are presented. We find that (1) generally, halogen substitutions would increase V_OC; (2) E_b rises with more fluorine substitutions, but for Cl and Br substitutions, E_b increases firstly and then drops; (3) ΔE_ST keeps increasing with more halogen substitutions; (4) except for Br substitutions, the averaged ESP arises along with more halogen substitutions; (5) the absorption strength of UV–Vis spectra of DRCN5T2F, DRCN5T4F, DRCN5T6F, and DRCN5T2Cl in the visible region is enhanced with respect to DRCN5T. Based on these results, overall, DRCN5T2Cl, DRCN5T4F, and DRCN5T6F may be promising donors.

Replacing the cyano (-C[triple bond, length as m-dash]N) group to design environmentally friendly fused-ring electron acceptors

The cyano-group (-C[triple bond, length as m-dash]N) is an electron-withdrawing group, which has been widely used to construct high-performance fused-ring electron acceptors (FREAs). Benefiting from these FREAs, the power conversion efficiency of organic solar cells has recently exceeded 18%. However, malononitrile is a highly toxic substance used to introduce -C[triple bond, length as m-dash]N during the synthesis of these FREAs. Therefore, the synthesis processes of most high-performance FREAs are typically harmful to the environment. Our previous work demonstrated that the electron-withdrawing ability of -C[triple bond, length as m-dash]N is necessary for FREAs. Thus, the use of other electron-withdrawing groups instead of -C[triple bond, length as m-dash]N to design environmentally friendly FREAs is feasible. We utilized seven electron-withdrawing groups, namely, -C[double bond, length as m-dash]NH, -N[double bond, length as m-dash]O, -CH[double bond, length as m-dash]O, -CO-CH3, -CO-OH, -CO-Cl, and -CO-Br, to replace -C[triple bond, length as m-dash]N in the commonly used acceptor Y6 to design new FREAs (Y6-CNH, Y6-NO, Y6-CHO, Y6-COCH3, Y6-COOH, Y6-COCl, and Y6-COBr). Multi-scale theoretical calculation methods were used to investigate the photoelectronic properties of these new FREAs, including energy level, absorption spectrum, exciton binding energy, and electron mobility. The results showed that Y6-CNH, Y6-COCH3 and Y6-COOH are unsuitable for use as acceptor materials because of their high frontier molecular orbital energy level and weak electron affinity. The strong absorption intensity and weak exciton binding energy of Y6-CHO, Y6-COCl, and Y6-COBr indicated that they can absorb more solar energy than Y6 and excitons are easier to separate into free charges. The electron mobility of Y6-CHO (3.53 × 10^-4 cm² V^-1 s^-1) was found to be approximately 28 times that of Y6-COCl (1.24 × 10^-5 cm² V^-1 s^-1) and Y6-COBr (1.28 × 10^-5 cm² V^-1 s^-1). The possible synthetic routes to Y6-CHO are environmentally friendly. Therefore, -CH[double bond, length as m-dash]O is the most suitable electron-withdrawing group for constructing high-performance environmentally friendly FREAs. This work can provide a new molecular design perspective in experimental science for developing high-performance environmentally friendly FREAs.

Geometry dependence of excitonic couplings and the consequences for configuration-space sampling

Excitonic coupling plays a key role for the understanding of excitonic energy transport (EET) in, for example, organic photovoltaics. However, the calculation of realistic systems is often beyond the applicability range of accurate wavefunction methods so that lower-scaling semi-empirical methods are used to model EET events. In the present work, the distance and angle dependence of excitonic couplings of dimers of selected organic molecules are evaluated for the semi-empirical long-range corrected density functional based tight binding (LC-DFTB) method and spin opposite scaled second order approximate coupled cluster singles and doubles (SOS-CC2). While semi-empirically scaled methods can lead to slightly increased deviations for excitation energies, the excitonic couplings and their dependence on the dimer geometry are reproduced. LC-DFTB yields a similar accuracy range as density-functional theory (DFT) employing the ωB97X functional while the computation time is reduced by several orders of magnitude. The dependence of the exchange contributions to the excitonic couplings on the dimer geometry is analyzed assessing the calculation of Coulombic excitonic couplings from monomer local excited states only, which reduces the computational effort significantly. The present work is a necessary first step toward the simulation of excitonic energy transport using semi-empirical methods.

Synergistic vacancy defects and mechanical strain for the modulation of the mechanical, electronic and optical properties of monolayer tungsten disulfide

Monolayer transition metal dichalcogenides (TMDs) are the potential candidate materials in nanoelectronic and optoelectronic applications due to their unique physical and chemical properties. Although both defect and strain greatly alter the structural, physical and chemical properties of monolayer TMDs, the defective monolayer TMDs under applied strain have not been adequately studied. In this paper, the synergistic effects of sulfur vacancy defects and mechanical strain on the mechanical, electronic and optical properties of monolayer tungsten disulfide (WS2) have been systematically studied using first principles density functional theory. The results indicate that the sulfur vacancy formation energy increases linearly with increasing sulfur vacancy concentration under different strains. The strain energy and stress of monolayer WS2 with different sulfur vacancy concentrations increase with increasing applied strain in the strain range of -10% to 10%. The band gap of monolayer WS2 decreases with increasing sulfur vacancy concentration under different strains. Moreover, compared with unstrained conditions, 5% compressive strain increases the band gap at a larger vacancy concentration and the case is just opposite at a smaller vacancy concentration, while 5% tensile strain decreases the band gap. The band gap of monolayer WS2 with different sulfur vacancy concentrations firstly increases and then shrinks with increasing applied strain under compressive strain, whereas it decreases monotonically under tensile strain in the strain range of -10% to 10%. In the visible-light wavelength region, the out-of-plane absorption coefficient under different strains increases with increasing sulfur vacancy concentration. Furthermore, 5% compressive strain enhances the absorption coefficient and 5% tensile strain decreases the absorption coefficient. Hence, the synergistic effects of sulfur vacancy defects and mechanical strain in monolayer TMDs can open new avenues for their applications in nanoelectronic and optoelectronic devices.

Achieving Small Exciton Binding Energies in Small Molecule Acceptors for Organic Solar Cells: Effect of Molecular Packing

Because of strong exciton binding energy (E_b), an exciton dissociation process and extra energy losses are present in organic solar cells relative to inorganic and perovskite solar cells. Here, we calculated the E_b of a series of small molecule acceptors in solid crystals by a self-consistent quantum mechanics/embedded charge approach. The results show that the E_b values are substantially reduced from the gas phase to solid state because of electronic polarization (mainly from the induction effect of charges). Moreover, in contrast to little changes in the gas phase, the E_b in the solid state can vary significantly, indicating an important molecular packing effect. Remarkably, an extremely weak E_b of 0.04 eV is achieved in a three-dimensional packing crystal, which is comparable to the E_b of organo-lead trihalide perovskites. This work underlines the importance of three-dimensional molecular packing for achieving small E_b and will be helpful in reducing energy losses in organic solar cells.

Exploring the effects of axial halogen substitutions of boron subphthalocyanines on the performance of BsubPC/C60 organic solar cells: a DFT/TDDFT-based computational study

A systematic study on the effects of axial halogen substitutions of Cl atom on the optical and physical properties of subphthalocyanine/C60 solar cells by combining a DFT/TDDFT study and available experimental data.

Theoretical investigation of the use of nanocages with an adsorbed halogen atom as anode materials in metal-ion batteries

The applicability of C₄₄, B₂₂N₂₂, Ge₄₄, and Al₂₂P₂₂ nanocages, as well as variants of those nanocages with an adsorbed halogen atom, as high-performance anode materials in Li-ion, Na-ion, and K-ion batteries was investigated theoretically via density functional theory. The results obtained indicate that, among the nanocages with no adsorbed halogen atom, Al₂₂P₂₂ would be the best candidate for a novel anode material for use in metal-ion batteries. Calculations also suggest that K-ion batteries which utilize these nanocages as anode materials would give better performance and would yield higher cell voltages than the corresponding Li-ion and Na-ion batteries with nanocage-based anodes. Also, the results for the nanocages with an adsorbed halogen atom imply that employing them as anode materials would lead to higher cell voltages and better metal-ion battery performance than if the nanocages with no adsorbed halogen atom were to be used as anode materials instead. Results further implied that nanocages with an adsorbed F atom would give higher cell voltages and better battery performance than nanocages with an adsorbed Cl or Br atom. We were ultimately able to conclude that a K-ion battery that utilized Al₂₁P₂₂ with an adsorbed F atom as its anode material would afford the best metal-ion battery performance; we therefore propose this as a novel highly efficient metal-ion battery. Graphical abstract The results of a theoretical investigation indicated that Al₂₂P₂₂ is a better candidate for a high-performance anode material in metal-ion batteries than Ge₄₄ is. Calculations also showed that K-ion batteries with nanocage-based anodes would produce higher cell voltages and perform better than the equivalent Li-ion and Na-ion batteries with nanocage-based anodes, and that anodes based on nanocages with an adsorbed F atom would perform better than anodes based on nanocages with an adsorbed Cl or Br atom.

Electronic and structural properties of fluorene–thiophene copolymers as function of the composition ratio between the moieties: a theoretical study

Through theoretical analysis, we study relevant properties of some molecular structures formed by oligothiophenes (T) and dioctylfluorenes (F) units, like the exciton binding energy (E_b) and dipole moment, important for the efficiency of different kinds of optical and electronic devices.

da Silva JJ, dos Santos RCR, Sales FAM, Gottfried C, S. Caetano EW, Freire VN. First-generation antipsychotic haloperidol: optical absorption measurement and structural, electronic, and optical properties of its anhydrous monoclinic crystal by first-principle approaches

Application of the Density Functional Theory for the structural, electronic and optical properties of haloperidol crystal.

Non-Fullerene Acceptor-Based Solar Cells: From Structural Design to Interface Charge Separation and Charge Transport

The development of non-fullerene small molecule as electron acceptors is critical for overcoming the shortcomings of fullerene and its derivatives (such as limited absorption of light, poor morphological stability and high cost). We investigated the electronic and optical properties of the two selected promising non-fullerene acceptors (NFAs), IDIC and IDTBR, and five conjugated donor polymers using quantum-chemical method (QM). Based on the optimized structures of the studied NFAs and the polymers, the ten donor/acceptor (D/A) interfaces were constructed and investigated using QM and Marcus semi-classical model. Firstly, for the two NFAs, IDTBR displays better electron transport capability, better optical absorption ability, and much greater electron mobility than IDIC. Secondly, the configurations of D/A yield the more bathochromic-shifted and broader sunlight absorption spectra than the single moiety. Surprisingly, although IDTBR has better optical properties than IDIC, the IDIC-based interfaces possess better electron injection abilities, optical absorption properties, smaller exciton binding energies and more effective electronic separation than the IDTBR-based interfaces. Finally, all the polymer/IDIC interfaces exhibit large charge separation rate (KCS) (up to 1012⁻1014 s-1) and low charge recombination rate (KCR) (<10⁶ s-1), which are more likely to result in high power conversion efficiencies (PCEs). From above analysis, it was found that the polymer/IDIC interfaces should display better performance in the utility of bulk-heterojunction solar cells (BHJ OSC) than polymer/IDTBR interfaces.

Role of exact exchange in thermally-assisted-occupation density functional theory: A proposal of new hybrid schemes

We propose hybrid schemes incorporating exact exchange into thermally assisted-occupation-density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] for an improved description of nonlocal exchange effects. With a few simple modifications, global and range-separated hybrid functionals in Kohn-Sham density functional theory (KS-DFT) can be combined seamlessly with TAO-DFT. In comparison with global hybrid functionals in KS-DFT, the resulting global hybrid functionals in TAO-DFT yield promising performance for systems with strong static correlation effects (e.g., the dissociation of H₂ and N₂, twisted ethylene, and electronic properties of linear acenes), while maintaining similar performance for systems without strong static correlation effects. Besides, a reasonably accurate description of noncovalent interactions can be efficiently achieved through the inclusion of dispersion corrections in hybrid TAO-DFT. Relative to semilocal density functionals in TAO-DFT, global hybrid functionals in TAO-DFT are generally superior in performance for a wide range of applications, such as thermochemistry, kinetics, reaction energies, and optimized geometries.

DFT study of opto-electronic properties of benzothiazole derivatives for use in solar cells

A variety of organic donor–acceptor–donor materials based on thienylbenzothiadiazole (BTD[Formula: see text]–5) combined with different [Formula: see text]-conjugated systems are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) for the ground- and excited-state properties, respectively, using B3LYP and the 6-31G(d, p) basis set. The effect of different electron-donor groups on the structural, electronic and optoelectronic properties is studied. To provide for the bandgap and to guide the synthesis of novel low bandgap materials, we applied quantum chemistry techniques to calculate the difference in the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital LUMO energies. However, we have studied the effect of the reduction and oxidation properties on the electronic excitation transitions for all compounds. The emission energies have been obtained from TD-DFT calculations performed on the excited-state optimized S1 geometries. The theoretical results suggest that both the introduction of electron-donor groups and the doping process contribute significantly to the electronic and optoelectronic properties of the alternating donor–acceptor–donor conjugated systems studied.

The van der Waals interactions in rare-gas dimers: the role of interparticle interactions

We investigate the potential energy curves of rare-gas dimers with various ranges and strengths of interparticle interactions (nuclear–electron, electron–electron, and nuclear–nuclear interactions).

Electronic and Optical Properties of the Narrowest Armchair Graphene Nanoribbons Studied by Density Functional Methods

In the present study, a series of planar poly(p-phenylene) (PPP) oligomers with n phenyl rings (n = 1–20), designated as n-PP, are taken as finite-size models of the narrowest armchair graphene nanoribbons with hydrogen passivation. The singlet-triplet energy gap, vertical ionization potential, vertical electron affinity, fundamental gap, optical gap, and exciton binding energy of n-PP are calculated using Kohn-Sham density functional theory and time-dependent density functional theory with various exchange-correlation density functionals. The ground state of n-PP is shown to be singlet for all the chain lengths studied. In contrast to the lowest singlet state (i.e., the ground state) of n-PP, the lowest triplet state of n-PP and the ground states of the cation and anion of n-PP are found to exhibit some multi-reference character. Overall, the electronic and optical properties of n-PP obtained from the ωB97 and ωB97X functionals are in excellent agreement with the available experimental data.

Assessment of the LFAs-PBE exchange–correlation potential for high-order harmonic generation of aligned H2+ molecules

We examine the performance of the LFAs-PBE exchange-correlation potential for the HHG spectra and related properties of H₂⁺ molecules aligned parallel and perpendicular to the polarization of an intense linearly polarized laser pulse.