Density Of States Analysis Research Articles

Multiple modulation of magnetism in two-dimensional FeCl2/In2Se3 van der Waals heterostructure

The effective modulation of magnetism for two-dimensional (2D) materials not only has potential applications in nanoscale spintronic devices but also has urgent demands in modern industries. In this work, we report the discovery of ferroelectrically (FE) tunable orbital reconstruction in FeCl2/In2Se3 2D van der Waals (vdWs) heterostructures (HSs), which leads to a transition from ferromagnetic (FM) order to ferrimagnetic order (intra-layer magnetic coupling is AFM3 arrangement). The reversible FE polarization not only enables the easy magnetization axis to be tuned from the out-of-plane to in-plane direction but also reduces the net magnetization strength from 31.87 to −0.18 μB/f.u. Based on the charge density differences and the density of states analysis, the preference of FM and AFM3 arrangement can be reasonably explained by the Goodenough–Kanamori–Anderson rule. The ferroelectric switching enables nonvolatile electric control of magnetic order and anisotropy, offering significant potential for high-efficiency nanodevices and nonvolatile information storage. Moreover, modulation of magnetism (magnetic moment from −0.18 to 0.18 μB/f.u.) can also be achieved through interlayer sliding in the −P case, providing a way to control magnetism in 2D vdWs HSs.

Na3VMn0.5Ti0.5(PO4)3/C with active Na+ hopping sites for high-rate and durable sodium-ion batteries

This study established the carbon-coated Na3VMn0.5Ti0.5(PO4)3/C (NVMTP/C) as a high-energy cathode material of the NASICON family for next-generation sodium-ion batteries (SIBs). When subjected to electrochemical sodium storage testing, the NVMTP/C cathode provided a stable specific capacity of 160.3 mAh g-1 with three electron reactions (average working voltage ∼3.4 V) during the Na+ (de)insertion routine, achieving a superior energy output of 544 Wh kg−1 among the NASICON family of SIBs. Benefiting from the characteristic NASICON structure and established multiple redox couples, the cathode delivered excellent rate capability (82 mAh g-1 at 17 C, 1 C = 176 mAh g-1), in addition to excellent cycling permanence at low and high current surges (104 mAh g-1 after 500 cycles at 0.85 C and 84 mAh g-1 after 3000 cycles at 11.34 C, respectively). Computational studies based on first principle calculations and density of states (DoS) attributed the superior electrochemical properties of NVMTP/C cathode to its substantial Na+ hopping sites facilitating the unhindered multi-electron transfer reactions (V2+/3+, V3+/4+, Ti3+/4+, and V4+/5+) reversibly at their respective redox potentials. The detailed DoS analysis revealed that the varying electronic configuration due to the co-swapping of Ti and Mn significantly uplifts the electronic conductivity of the NVMTP/C cathode. Further calculation studies clearly indicate lower activation energy for active Na+ hopping and hence faster Na-diffusion thus suggesting that the present NVMTP/C cathode can have definite commercial prospects.

Adsorption and sensing properties of ZrSe2 monolayer modified with transition metal for CO2, NO2 and SO2 gases: First-principles calculations

In this study, the adsorption of three industrial gases (CO2, NO2 and SO2) on ZrSe2 monolayers with modified transition metal (TM=Y, Zr, Nb, Mo, Rh, Ru, Pd, Ag) are calculated using first-principles methods for possible applications of different TM-ZrSe2 as industrial gas sensors and adsorbents. Studying the density of states (DOS), adsorption energy (Eads), charge transfer (Q), charge difference density (CDD), work function (W) and recovery time of three kinds of gas molecules adsorbed on TM-ZrSe2 monolayers and their sensing performance are evaluated. The findings reveal that CO2 gas molecules are more likely to be adsorbed on Zr-ZrSe2 monolayer, NO2 is apt to be adsorbed on Y-ZrSe2 monolayer, and SO2 gas molecules have stronger adsorption behavior on Zr-ZrSe2 monolayer. The analysis of CDD and DOS shows that the Eads of gas molecules are related to charge transfer and orbital hybridization. Additionally, the degree of electron migration is shown by the transformation of the work function's magnitude. In summary, the effectiveness of TM-ZrSe2 as sensing materials in various gas sensors is assessed, and the desorption times are compared. We anticipate that this work will offer fresh perspectives and a theoretical basis for the possible application of the TM-ZrSe2 monolayer layer to the sensing and processing of three gases.

Influence of azo-based donor modifications on nonlinear optical amplitude of D-π-A based organic chromophores: A DFT/TD-DFT exploration

Organic heterocyclic fused ring compounds possess remarkable nonlinear optical (NLO) amplitude, are potentially employed in optical computing and nano-photonics. Herein, ITTBCR1 was quantum chemically modified into a series of novel D-π-A configured NLO compounds (ITTBCD2-ITTBCD6) by substituting various efficient donor moieties. To investigate the electronic, photophysical, and NLO properties, ITTBCR1 and ITTBCD2-ITTBCD6 were subjected to density functional theory (DFT) and time-dependent DFT calculations at M06/6–311 G(d,p) level of theory. Frontier molecular orbital analysis (FMOs) illustrated that the newly designed chromophores exhibit smaller energy gaps (1.625–2.013 eV) compared to ITTBCR1 (2.384 eV). The global reactivity parameters estimated through Egap revealed higher softness (σ = 0.49–0.61 Eh) values, implying enhanced reactivity of ITTBCD2-ITTBCD6 compounds. An efficient push-pull mechanism disclosed positive charges on donors and π-spacers, while the acceptor moieties exhibited a negative charge. The presence of charge separation states and the substantial involvement of molecular orbitals in the charge transfer were explored by natural bond orbitals (NBOs), transition density matrix and density of states analyses. The UV-Vis study of the designed compounds displayed larger bathochromic shifts with wider absorption spectra. Also, a significantly large NLO behavior was found in all the novel entities (ITTBCD2-ITTBCD6), thus potentially employable as NLO materials. Inclusively, compound ITTBCD5 demonstrated highest linear polarizability (〈α〉 = 2.250 ×103a.u.), and first hyperpolarizability (βtot = 70.155 ×104a.u.), therefore proposed as the most proficient NLO material. Comparative study for NLO properties at various functional showed that at M06/6–311 G (d,p) significant NLO results could be obtained. The current investigation revealed that by controlling the type of donor motifs, numerous NLO compounds can be designed, which are equally productive in hi-tech NLO applications.

The interaction mechanism and collecting performance of three sulfydryl collectors with Au(1 0 0) surface: A study combining DFT and molecular dynamics

Amyl xanthate (AMX), ammonium dibutyl dithiophosphate (ADD) and diisobutyl dithiophosphinate (DTPI) have proved to be common and effective sulfydryl collectors for gold flotation. In this study, density functional theory (DFT) and molecular dynamics (MD) methods are used to investigate the interaction mechanism and collecting performance of three sulfydryl collectors with Au(100) surface. The adsorption energy of DTPI is −283.30 kJ/mol, which is the largest among the three, suggesting its chemisorption on gold surface is the most stable. This is agreed with the prediction of polarizability and frontier orbital energy difference. The gold-collector interaction on the surface is realized by the bonding of surface Au atom and collector S atom. Density of states (DOS) results suggest that after collector adsorption the delocalization of S 3p orbital is increased, resulting in the enhancement of nephelauxetic effect, and this proves that the covalency of Au − S bond has been facilitated. DOS analysis further confirms that the S atom of DTPI is most likely to form a covalent bond with Au atom because of its strongest reactivity. Besides, molecular dynamics simulation suggests that the wetting process of water droplets on the gold surface would be hindered by the adsorption of three collectors, thus the wettability of the gold surface would change significantly. In summary, it can be considered that the gold collecting performance of three collectors follows the order of DTPI > ADD > AMX. This comparative study is helpful to understand the interaction mechanism between sulfydryl collectors and gold surface.

Reaction mechanism between Gen (n = 2–5) clusters and single water molecule based on density functional theory

AbstractThe ground state structures of Gen (n = 2–5) clusters and their adsorption energy values with single water molecule were calculated using density functional theory. We also investigated the reaction pathways between Gen (n = 2–5) clusters and single water molecule. Based on molecular orbital and natural population analysis (NPA) figures, it was found that the O atom in H2O binds to the Gen (n = 2–5) clusters to form GenO (n = 2–5) and releases hydrogen. Notably, the Ge2 cluster exhibited the most efficient interaction with single water molecule based on the comparison of the energy values during the reaction of hydrogen generation. Furthermore, NPA and density of states analyses indicate that the Ge atoms in the products did not reach their highest oxidation state, suggesting that GenO (n = 2–5) may continue to react with more water molecules to generate hydrogen. Our results provide a deeper understanding of the chemical reaction properties.

Stability and electronic properties of low-index surfaces of zinc stannate modulated by vacancy defect: A first-principle study

The low-index surfaces and defect structures of perovskite zinc stannate (ZTO) were studied based on the first-principles density functional theory (DFT) calculations. The geometry, stability and electronic properties of zinc stannate modulated by point defects were discussed. It is found that the 001 surface of ZTO and its oxygen defects on the surface were most stable thermodynamically among the 42 low-dimensional structures according to the energy calculations. The electronic properties near the Fermi level of low-dimensional ZTO structures can be modulated by different defects. This can be understood by electron band structure and density of states analysis. 101 surface of ZTO showed a metallic characteristic, while other low-dimensional ZTO structures were all semiconductors with a decreased band gap than that of the bulk. Defects could induce electron transfer and charge re-distribution on the ZTO surface by means of geometric and chemical bonding reconstruction on surfaces with defects.

Ab initio study of the newly proposed full Heusler alloy Co2CuAl : Insights from DFT

The Wien2k code is used to investigate the structural and electronic properties of Co2CuAl using tools of Density Functional Theory (DFT). In light of different exchange correlation potentials, we have obtained the information about optimized crystal structural, density of states (DOS), and band structure of possible non-magnetic and spin polarisation phases of this alloy. Structure optimization analysis revealed that the alloy is stable in the spin-polarised (SP) phase. Further the analysis of electronic DOS and band structure show the presence of anisotropic semi-metallic behaviour and indicate the potential of Co2CuAl to be a novel Heusler alloy.

Analysis of the electronic structure of β-SiO2 intrinsic defects based on Density Functional Theory

In order to characterize the effect of β-SiO2 intrinsic defects on the properties of the perfect structure, the electronic properties of the perfect β-SiO2 and its four typical intrinsic defects under the generalized gradient approximation (GGA) based on Density Functional Theory (DFT) were performed, and the defect formation energy, energy band, density of states (DOS) and differential charge density were calculated. The defect formation energy calculation results showed that interstitial defects were easier to form but less stable than vacancy defects. Meanwhile, the analysis of energy band and DOS indicated that the perfect and defective structures of β-SiO2 were indirect band gap insulators. Furthermore, the appearance of DOS at the Fermi level in the silicon interstitial structure and the energy band passing through the Fermi level indicated that the conductivity of the structure was improved. Moreover, the study of differential charge density illustrated charge transferred from silicon atoms to oxygen atoms, and Si-O covalent bonds with strong polarity were formed between silicon and oxygen atoms. Our studies could provide a theoretical basis for the study of the evolution of intrinsic defects and damages in ultra-precision machining such as ion beam figuring.

In Silico Designing of Thieno[2,3-b]thiophene Core-Based Highly Conjugated, Fused-Ring, Near-Infrared Sensitive Non-fullerene Acceptors for Organic Solar Cells.

The performance of organic solar cells (OSCs) has been improving steadily over the last few years, owing to the optimization of device fabrication, fine-tuning of morphology, and thin-film processing. Thiophene core containing fused ring-type non-fullerene acceptors (NFAs) achieved significant proficiency for highly efficient OSCs. Quantum chemical computations are utilized herein with the motive of suggesting new NIR sensitive, highly efficient low-band gap materials for OSCs. A series of extended conjugated A-π-D-π-A architectured novel fused-ring NFAs (FUIC-1-FUIC-6) containing thieno[2,3-b]thiophene-based donor core are proposed by substituting the end-capped units of synthesized molecule F10IC. Different properties including frontier molecular orbital analysis, density of states analysis, transition density matrix analysis, excitation energy, reorganizational energies of both holes (λh) and electrons (λe), and open-circuit voltage (V oc) were performed employing the density functional theory approach. Charge transfer analysis of the best-designed molecule with the donor complex was analyzed to comprehend the efficiency of novel constructed molecules (FUIC-1-FUIC-6) and compared with the reference. End-caped acceptor alteration induces the reduction of the energy gap between HOMO-LUMO (1.88 eV), tunes the energy levels, longer absorption in the visible and near-infrared regions, larger V oc, smaller reorganizational energies, and binding energy values in designed structures (FUIC-1-FUIC-6) in comparison to reference (FUIC). The designed molecules show the best agreement with the PTBT-T donor polymer blend and cause the highest charge from the HOMO to the LUMO orbital. Our findings predicted that thieno[2,3-b] thiophene-based newly designed molecules would be efficient NFAs with outstanding photovoltaic characteristics and can be used in future applications of OSCs.

Calculation of excited states of monolayer TPPA-COF based on first principles.

Two-dimensional covalent organic frameworks (COFs) have always been a hot topic in condensed matter physics. Herein, the first 100 excited states of the TPPA-COF are calculated to investigate the optical absorption properties of the materials in the interval. The stable molecular structure of monolayer TPPA-COF is obtained by first-principles calculation, which can be regarded as a hexagon with an aperture size of 18.25 Å. By means of the band structure and density of state analysis, it is found that the monolayer band gap width of the TPPA-COF is 1.52 eV. All excited states of the TPPA-COF exhibit obvious pi → pi* (delocalized π to anti π) local excitation characteristics through analysing the spatial distribution of the electron-hole pairs of the 10 excited states with the highest oscillator strength among the first 100 excited states. In addition, the simulated UV-vis spectra show that the maximum absorption intensity of the TPPA-COF is about 357 684 mol-1 cm-1, indicating that the TPPA-COF is a potential light-absorbing material.

Synthesis, characterization and exploration of photovoltaic behavior of hydrazide based scaffolds: a concise experimental and DFT study.

Solar energy being a non-depleting energy resource, has attracted scientists' attention to develop efficient solar cells to meet energy demands. Herein, a series of hydrazinylthiazole-4-carbohydrazide organic photovoltaic compounds (BDTC1-BDTC7) with an A1-D1-A2-D2 framework was synthesized with 48-62% yields, and their spectroscopic characterization was accomplished using FT-IR, HRMS, 1H and 13C-NMR techniques. Density functional theory (DFT) and time dependent DFT analyses were performed utilizing the M06/6-31G(d,p) functional to calculate the photovoltaic and optoelectronic properties of BDTC1-BDTC7via numerous simulations of the frontier molecular orbitals (FMOs), transition density matrix (TDM), open circuit voltage (V oc) and density of states (DOS). Moreover, the conducted analysis on the FMOs revealed efficient transference of charge from the highest occupied to the lowest unoccupied molecular orbitals (HOMO → LUMO), further supported by TDM and DOS analyses. Furthermore, the values of binding energy (E b = 0.295 to 1.150 eV), as well as reorganization energy of the holes (-0.038-0.025 eV) and electrons (-0.023-0.00 eV), were found to be smaller for all the studied compounds, which suggests a higher exciton dissociation rate with greater hole mobility in BDTC1-BDTC7. V oc analysis was accomplished with respect to HOMOPBDB-T-LUMOACCEPTOR. Among all the synthesized molecules, BDTC7 was found to have a reduced band gap (3.583 eV), with a bathochromic shift and absorption maximum at 448.990 nm, and a promising V oc (1.97 V), thus it is regarded as a potential candidate for high performance photovoltaic applications.

In English

The hexagon-shape graphene nanoflakes (GNFs) limited by zigzag edges only (with doubly and triply coordinated atoms) have unique increased reactivity. Despite the high systems symmetry (D6h) the Carbon atoms in GNFs occupy non-equivalent positions. Can such physical and chemical characteristics of GNFs, which depend of the atom position in the cluster, definition? This characteristic together with the simplicity of its calculation makes it possible to predict the properties of nanoflakes obtained from GNFs by introducing single and multiatomic vacancies into them or by replacing Carbon atoms with electron withdrawing and electron donating atoms. This characteristic includes the C1s core-level binding energy shifts, the maxima of which characterize the C atoms of a certain type. The proposed work is devoted to quantum chemical calculations of the electronic density of states (DOS) of pristine hexagon-shape GNF C96 (multiplicity, M=5), their saturated counterpart –polycyclic aromatic hydrocarbon(PAH) C96H24 (M=1) and their derivatives with one and two single vacancies in the ground electronic state (GES). All calculations were performed using the density functional theory (DFT) method with the involvement of the valence-split basis set 6-31G (d,p). Systems with open shells were considered using the UB3LYP exchange-correlation functional. The obtained spectra were fitted using Gaussian curve fitting program to determine the binding energy for each peak. The Gaussian function distribution of the theoretically calculated C1s core-level binding energy shifts of GNFs testified the presence of six peaks, each of which refers to a certain type of Carbon atoms. The C1s peak with the highest binding energy (-285.57 eV) is caused by contributions from the doubly coordinated edge cyclic chain (ECC) Carbon atoms. The C1s orbitals of the central hexagon (CHex) atoms and the first cyclic chain (FCC) atoms form delocalized molecular orbitals (MOs) in different parts of the cluster. The analogous spectrum of PAH C96H24 is slightly shifted to the region of lower binding energies and contains only two well-defined peaks. The peak with a higher binding energy (-284.36 eV) is generated by the 1s states of the CHex atoms and the atoms of the FCC, which are bounded to the CHex atoms. The electronic DOS difference in C1s core-level spectra of GNF C96 (M=5) and their saturated counterpart PAH C96H24 is established due to the presence of two weakly bounded π-systems in GNF and common conjugated system in PAH. The electronic DOS of defect-containing cluster C96-1(1) (M=3) (one CHex atom has been removed from the C96nanoflake) is generated by the C1s core-level atoms of the second cyclic chain (SCC), which are located at the different distances from the center of the nanoflake. The peak of the lowest intensity (-284.63 eV) appears in the spectrum as a reflection of the appearance of doubly coordinated Carbon atoms surrounding the single vacancy in the C96-1(1) nanoflake. The analysis of the electronic DOS of the C1s core-level spectrum of the C96-2(1) nanoflakeis shown, that doubly coordinated Carbon atoms, concentrated around two single vacancies, are essentially non-equivalent. If the MO with the lowest binding energy is localized on two of them – the MO with the highest binding energy is localized on the third atoms (one around each single vacancy). The electronic C1s core-level DOS spectrum of defect-containing molecular systems with one C96-1(1)H24 and two C96‑2(1)H24 single vacancies are similar to the analogous spectrum of PAH C96H24. In the first of them – one additional maximum appears due to C1s atoms surrounding the single vacancy. In the second – there are two additional maxima, each of which is generated by C1s core-level atoms adjacent to individual vacancies.

Study of double perovskites In2Ti(Br/I)6 for solar cells, and renewable energy; Alternative of hybrid perovskites

The vacancy ordered double perovskites are become the potential materials for renewable and clean energy. Therefore, in present article, the In2TiBr6 and In2TiI6 are studied for electronic, optoelectronic, and thermoelectric properties. The existence of structures, and thermodynamic stability are explained by tolerance factor, and formation energy. The band structures and density of states analysis indicates the band gaps (2.2 eV, 1.4 eV) for In2Ti(Br/I)6, and recombination of carriers under ambient conditions. The absorption bands in visible regions 335 to 539 nm and 413 to 729 nm for In2TiBr6 and In2TiI6 are excellent for solar cells. The thermoelectric analysis describes high Seebeck coefficient, power factor and figure of merit values of the studied compounds which indicate potential thermoelectric applications especially in generators and thermally active optical sensors.

Structural Characteristics, Stability, and Electronic Properties of 001 Surface with Point Defects of Zinc Stannate: A First-Principle Study

This work presents first-principles calculations on the surface and defect impact upon zinc stannate (ZS) materials with perovskite bulk structures. The structure and electronic properties of both a perfect 001 surface and surfaces with a point defect of ZS were investigated by means of density functional theory calculations. The cohesive energies of a perfect 001 surface and those with O, Sn, or Zn defects were decreased compared with that of bulk ZS. Oxygen defects on the 001 surface of ZS formed more easily than others based on the obtained cohesive energy and defect formation energy. The electronic properties close to the Fermi levels of bulk ZS materials were mainly controlled by the O 2p and Sn 5s orbitals. The formation of vacancy on the 001 surface of ZS changed the band structure and band gap compared with that of the bulk. The modulation mechanism was explored by means of structure transformation, band structure, and density of states analysis.

High Curie Temperature and Half‐Metallic Ferromagnetism in ZnSe:Co,Ni with Wurtzite Structure: First‐Principles Study

The aim is to examine the spin‐polarized electronic band structures, the density of states (DOS) as well as magnetism of CoxZn1−xSe and NixZn1−xSe diluted magnetic semiconductors (DMSs) in the ferromagnetic (FM) phase, and with 12.5% and 6.25% concentrations of impurity. The calculations are implemented by the recent ab initio norm‐conserving FHI pseudopotential method within the local spin density approximation and Hubbard U (LSDA + U) method. The analysis of the total DOS (TDOS) curves shows the half‐metallic FM character for Ni‐doped and (Co, Ni)‐co‐doped ZnSe with a half‐metallic bandgap of 1 ÷ 1.6 eV. The exchange splittings produced by dopant d states are determined: for the CoxZn1−xSe, it is obtained that the effective potential for the majority spin is more attractive than for the minority spin. The total magnetic moments of Co‐doped, Ni‐doped, and co‐doped ZnSe DMSs are found to be equal to 3, 4, and 5.0 μB, respectively. The Curie temperature of NixZn1−xSe is higher than room temperature and this is half‐metallic ferromagnetic (HMFM) material for spintronics application. Co‐doped ZnSe is an excellent choice for electronic devices owing to its below Curie temperature.

First theoretical framework for highly efficient photovoltaic parameters by structural modification with benzothiophene-incorporated acceptors in dithiophene based chromophores

Now a days, researchers are constantly doing efforts to upgrade the performance of solar based devices with the aim of increasing the role of photovoltaic materials in modern hi-tech optoelectronic applications. Realizing the recent energy conditions across the globe, research is diverted from fullerene to non-fullerene electron acceptor moieties in this era, considering their remarkable contribution in organic solar cells (OSCs). Therefore, we designed seven novel non-fullerene fused ring electron acceptor chromophores (MD2–MD8) from DOC2C6-2F by structural tailoring with different acceptors at end-capped units. DFT study was performed at B3LYP functional to discover the opto-electronic characteristics of the newly tailored chromophores. Various analysis such as frontier molecular orbitals (FMOs), transition density matrix (TDM), density of states (DOS), binding energy (Eb), reorganization energy, open circuit voltage (Voc) was carried out to comprehend the photovoltaic response of MD2–MD8. Decrease in band gaps (1.940–1.571 eV) with wider absorption spectrum (725.690–939.844 nm in chloroform) along with greater charge transfer rate from HOMO towards LUMO were examined in derivatives as compared to MR1 (Egap = 1.976 eV, λmax = 738.221 nm) except MD7. Further, in all derivatives, smaller values of Eb (0.252–0.279 eV) were examined than that of reference (0.296 eV). These lower binding energy values of MD2–MD8 indicated the higher rate of excitation dissociation with lager charger transfer rate than MR1, which further supported by DOS and TDM analyses. Additionally, least reorganization energy in the aforesaid compounds for hole with electron was also inspected. Moreover, Voc a good photovoltaic response was noted for all studied compounds which indicated that these compounds are suitable to synthesize OSCs in future.

Adsorption Properties and Quantum Molecular Descriptors of the Anticancer Drug Cytophosphane on the Armchair Single-Walled Carbon Nanotubes: A DFT Study

Abstract: In the current work, the adsorption of cytophosphane (cytophosphane is a chemotherapeutic drug and is used to treat several specific autoimmune diseases and malignant processes) on the (5,5) SWCNT was studied using density functional theory (DFT) calculations in terms of geometry, energy gap, charge transfer, molecular electrostatic potential surface, and density of state analysis. The behavior of the binding properties and the electronic structures revealed that the cytophosphane molecule could be adsorbed on the SWCNT by the adsorption energy of approximately -100.3 kcal mol-1. Also, it was found that the electronic properties of the SWCNT are very sensitive to the presence of cytophosphane molecules so that the energy gap of the nanotube is changed about 61% after the adsorption process. Based on calculated results, the SWCNT is expected to be suitable as a drug carrier for the delivery of cytophosphane drug.

Carbazole-based donor materials with enhanced photovoltaic parameters for organic solar cells and hole-transport materials for efficient perovskite solar cells.

Five carbazole-based donor molecules are designed by structural engineering of reference molecule PF. The molecules are devised by substitution of thiophene bridged end-capped acceptor groups namely (2-methylenemalononitrile) PF1, (methyl 2-cyanoacrylate) PF2, (3-methyl-5-methylene-2-thioxothiazolidin-4-one) PF3, (2-(3-methyl-5-methylene-4-oxothiazolidin-2- ylidene) malononitrile) PF4, and (4-(5-methylthiophen-2-yl) benzo[c] [1, 2, 5] thiadiazol) PF5. A DFT investigation was performed at the selected DFT functional MPW1PW91/6-31G (d,p) to investigate the optoelectronic properties of PF and all designed (PF1-PF2) molecules. Several important characteristics, i.e., band gap (Eg), transition density matrix analysis, dipole moment (µ), density of states analysis, reorganization energies, open circuit voltage (Voc), and fill factor, were investigated. The comparison of energy levels of reference molecule and designed molecules unveils the fact that these molecules are efficient hole transport materials to be used in perovskite solar cells (PSCs). All the newly drafted molecules (PF1-PF5) show higher λmax values in solvent (Chlorobenzene) ranging from 529 to 614nm than the reference PF (344nm). Smaller band gap (Eg) values in a range of 2.27-1.9eV for newly designed molecules are observed which are very much reduced when compared to reference PF. Lowered exciton binding energies (Eb) and reorganization energies for the electron (0.004279-0.0103337eV) as compared to PF reveal that our molecules display higher electron mobility rates, and hence, these small molecules can be used as proficient donor materials in high-performance organic solar cells (OSCs) and better hole transport materials (HTMs) for possible application in perovskite solar cells.

Structural evolution and bonding characteristics of neutral Cs2B n clusters

In this study, the unbiased crystal structure analysis by particle swarm optimisation (CALYPSO) combined with the density functional theory (DFT) method were used to perform a structure search for neutral Cs2B n (n = 1–12) clusters, as well as the corresponding global minimum of the potential energy surface were determined. The ground-state structures of the Cs2B n (n = 1–12) clusters have four types of geometries: planar, arch bridge, double pyramid, and shield shape. Subsequently, the relative stability of the ground-state structures was systematically analysed based on three effective rules, which indicates that the C7V Cs2B8 with a double pyramid structure has unusual stability. The results of the molecular orbitals (MOs) and density of states analysis (DOS) show that the B-2s and 2p atomic orbitals of Cs2B8 are the main components of MOs. In addition, from the results of adaptive natural density partitioning (AdNDP) and localised orbital locator (LOL), it can be seen that the excellent stability of Cs2B8 originates from the delocalised large π bonds with aromaticity and the s–p bonding of B–B. Our results reveal the structural growth mode of Cs2B n clusters and enrich the chemical bonding properties of boron-based clusters.