Difference Electron Density Map Research Articles

Synthesis, spectral, crystal structure, linear and NLO properties of quinoline Schiff base: Combined experimental and DFT calculations

The study explores the optical and nonlinear optical (NLO) properties of 2-imino [N- (N'-amido phenyl)] chromophore, a compound with potential in photonic applications. The compound was produced and crystallized using a slow evaporation approach using ethanol as solvent, and spectroscopy techniques were used to characterize it. The molecular structure of the compound was determined using FT-IR and NMR spectral methods. The crystal's structure was found via SCXRD analysis, showing a monoclinic system with a P21/c space group. The UV–Vis-NIR spectrum showed good transmittance over the visible region, with lower cutoff wavelengths of 338 nm and optical band gaps of 3.17 eV. The grown crystal exhibited a χ3 value of 2.89 × 10−8esu, making it valuable for non-linear optical applications. Quantum computational analysis was used to investigate molecular architectures, topologies, and molecule-level third-order NLO response. The compound exhibited a planar molecular geometry, with an average third-order NLO polarizability of 69.65 × 10−36 esu. The study also examined quantum chemically computed UV–visible spectra and electron density difference maps, as well as the density of states and molecular electrostatic potentials. In addition to highlighting the relationship between structure and characteristics, our current study of synthesized compounds highlights the potential of photonic applications.

A novel MoS2/Pd5 nanocluster heterojunction system with improved surface reactivity for efficient gas sensing: A DFT study

Our work has reflected considerable interest in unique Pd nanocluster/MoS2 heterojunction systems due to their potential applications in materials science, chemistry and physics. We focused on exploiting Pd5/MoS2 nanocluster system, a novel heterojunction material for gas sensing applications. In addition, we exploited the electronic properties of Pd dopant on the MoS2 surface to make a comparative study. Our DFT calculations indicate that the Pd5/MoS2 heterojunction structure exhibits a higher affinity for adsorbing gas molecules such as CO, NH3, NO, and NO2, while the perfect MoS2 shows weak gas adsorption capacity. Pd5/MoS2 heterojunction exhibits semiconducting feature with a weakened and narrower band gap, making it more suitable for gas sensing due to its higher conductivity. We analyzed important factors like adsorption distance/energies, density of states, band structure and difference of electron density concerning adsorbed gases on the heterojunction surface. Based on the electron density difference maps, we can see the giant growth of charges over the adsorbed molecules, as well as between the adsorbing atoms. Based on our findings, the conductivity of the nanomaterial undergoes a remarkable change, which helps reinforce the applicability of the Pd5/MoS2 heterojunction nanosystem in sensing and adsorbing gas molecules.

To Examine the Adsorption Behavior and Dissociation of Hydrogen Selenide (H2Se) Gas on Pristine and Transition‐Metal (Fe, Mn)‐Doped Boron Nitride Nanosheets: A DFT Study

AbstractIn this study, the adsorption and dissociation of H2Segas on pristine and transition metal (TM) atoms doped nanosheets have been investigated theoretically using density functional theory (DFT) calculations. To understand the adsorption mechanics, we have examined the adsorption energy, the charge transfer between the adsorbent and adsorbate, the band structure, the density of states (DoS), as well as the optical properties. The structural stability of TM atoms (Fe, Mn)‐ doped BN nanosheets have been verified by finding the cohesive energy. The adsorption energies of H2Se on pristine BN, Fe–BN, and Mn–BN sheets are −0.012, −7.627, and −10.001 eV, respectively; that is, the H2Se gas get dissociated when interacted with the Fe–BN and Mn–BN nanosheets. The relaxed geometrical structures of complexes and electron density difference (EDD) map analysis displayed that the H2Se gas makes bond with TM‐doped nanosheets, that is, dissociated. Furthermore, we viewed the optical properties of the pure, TM‐doped nanosheets as well as the gas‐adsorbed complex structure to demonstrate the adsorption behavior. Therefore, our obtained results demonstrated that the Fe‐ and Mn‐doped BN sheets are good candidates for adsorption and dissociation of H2Se gas.

Adsorption of Imidazolium‐Based Ionic Liquid On Pt(111) Surface Studied Using Density Functional Theory

AbstractThe strength and nature of adsorption of imidazolium‐based tetraflouroborate ionic liquid (IL) on platinum surface has been investigated via first principle‐based density functional theory method. Adsorption of both IL cation and IL ion‐pair as a function of increasing alkyl chain length is taken into consideration. Three different orientations of ionic liquid cations are found to be stable with higher adsorption energy noticed for the alkyl chain parallel to the platinum surface. The anions are found to stabilize the IL cation orientation where the alkyl chain is oriented perpendicular the platinum surface. These results are further corroborated by the charge transfer analysis and electron density difference maps. The significant charge transfer between the ionic liquid pair and the surface indicates electrochemical applications for systems involving electrolytes and metal surface, where electrostatic interactions play a major role. The results of this investigation can be helpful for further analysis of electrode–electrolyte systems as well as the development of force field parameters for these systems.

Theoretical investigation of benzodithiophene-based donor molecules in organic solar cells: from structural optimization to performance metrics.

Achieving high power conversion efficiency (PCE) remains a significant challenge in the advancement of organic solar cells (OSCs). In the field of organic photovoltaics (OPVs), considerable progress has been made in optimizing molecular structures to improve the PCE. However, innovative material design strategies specifically aimed at enhancing PCE are still needed. Here, we have designed BDTS-2DPP-based molecules and propose a molecular design approach to develop donor materials that can significantly improve the PCE of OSCs. Density functional theory (DFT) and time-dependent DFT (TD-DFT) methods have been adopted in both gas and solvent phases. Our newly designed molecule M1 shows the highest absorption value (λ max = 846 nm), highest electron reorganization energy (λ e = 0.18 eV), and the lowest energy gap (E g = 1.81 eV) among all the designed molecules. M1 molecule also exhibits the highest dipole moment in both gas (10.62 D) and solvent phase (13.62 D), and their ground and excited state dipole moment difference is also higher (μ e - μ g = 2.99 D), which enhances its separation to make it a suitable candidate for charge transfer between HOMO-LUMO (97%). Newly designed molecule M3 is observed to have the highest voltage when the current is zero (V oc = 1.15 V) highest PCE value (21.90%) and highest fill factor (FF) value (89.42%). The lowest excitation binding energy is estimated by newly designed molecule M2 (E b = 0.30 eV), which indicates a higher rate of dissociation during the excitation as observed in transition density matrix (TDM) plots. Utilizing electron density difference maps, the newly designed molecules in dichloromethane solvent exhibited consistent intramolecular charge transfer (ICT). The designed molecules were evaluated against reference molecule R to determine if they exhibit superior optoelectronic capabilities. It is found that all designed molecules (M1-M5) exhibit reduced band gaps, are red-shifted in wavelength in comparison to a reference molecule R, and have remarkable charge motilities in terms of reorganisation energies.

Theoretical study on the enhanced nonlinear optical responses of sulflowers and selenosulflowers

To develop highly efficient NLO materials for optoelectronic applications, theoretically, superhalogen-doped sulflower and selenosulflower were studied. The DFT/B3LYP-D3/6–311++G(2d,2p) basis set is used to complete the inquiry. The NLO properties of these complexes were assessed using, vertical ionization energy, and Electron Density Difference Map (EDDM) methods. The EDDM results reveal the electron transfer from sulflower to superhalogens leads to a donor–acceptor mechanism, which enhances hyperpolarizability. Superhalogen-doped sulflowers exhibit more prominent NLO properties than the undoped ligands, including static and dynamic NLO characteristics. This enhancement is due to the distortion of centrosymmetry and charge transfer between the sulflower and the doped superhalogen.

Eggshell-enhanced biochar with in-situ formed CaO/Ca(OH)2 for efficient removal of Pb2+ and Cd2+ from wastewater: Performance and mechanistic insights

This study proposes a green and simple strategy for efficiently removing heavy metals from wastewater by activating biochar with eggshell and in-situ generating CaO/Ca(OH)2. Characterization results revealed that the composite carbon material (BCEg15) successfully incorporated CaO/Ca(OH)2 active sites compared to the raw biochar (BC). Additionally, eggshell activation increased the specific surface area and pore volume of BCEg15 by 4.36 and 6.80 times, respectively, compared to BC. These structural enhancements increased the maximum adsorption capacity of BCEg15 for Pb2+ and Cd2+ by 20.68 and 42 times, respectively, compared to BC. Importantly, the loading of CaO and Ca(OH)2 significantly enhanced the ion exchange and mineral precipitation capacities of the biochar. For instance, compared to BC, the adsorption capacities of BCEg15 attributed to ion exchange (Qe) for Pb2+ and Cd2+ rose by 403.12 mg/g and 197.65 mg/g, respectively, while the adsorption capacities attributed to mineral precipitation (Qp) increased by 19.60 times and 45.20 times, respectively. BCEg15 demonstrated excellent reusability, maintaining adsorption capacities of 461.18 mg/g for Pb2+ and 265.26 mg/g for Cd2+ after five cycles. Additionally, BCEg15 outperformed commercial activated carbon in treating heavy metals from desulfurization wastewater from coal-fired power plants, achieving a removal efficiency of 99.98 % compared to 48.22 %. The primary mechanisms by which BCEg15 removes Pb2+ and Cd2+ were identified as ion exchange, mineral precipitation, complexation with oxygen-containing functional groups, and interactions with π electrons. Density functional theory (DFT) was utilized to delve deeper into the microscopic mechanisms of adsorption. The findings showed that the O-top site of CaO exhibited the greatest stability for heavy metal adsorption. Electron density difference maps and partial density of states (PDOS) results revealed a denser electron cloud and greater orbital overlap between CaO and Pb2+ compared to Cd2+, suggesting a higher affinity and adsorption capacity for Pb2+, consistent with the experimental findings. This study presents an effective method for preparing adsorbents capable of removing Pb2+ and Cd2+ from wastewater and offers theoretical insights into the adsorption mechanisms of metal oxide-incorporated biochar.

Theoretically designed M@diaza[2.2.2]cryptand complexes: the role of non-covalent interactions in promoting NLO properties of organic electrides

ABSTRACT Organic excess electron compounds with significant nonlinear optical (NLO) properties are widely employed in optoelectronic applications. Herein, single-alkali metals with diaza[2.2.2] cryptand (M@crypt,M=Li, Na, and K) are investigated for optoelectronic and NLO properties by using the density functional theory. Thermodynamic and kinetic stabilities of present complexes are computed through interaction energy (Eint) and ab-initio molecular dynamic (AIMD) simulations. M@crypt complexes carry excess electrons and mimic molecular electrides. Quantum theory of atoms in molecules (QTAIM) analysis and reduced density gradient (RDG) spectra demonstrate the roles of the weak van der Waals (vdW) interactions between metal and complexant. The remarkable hyperpolarizability (βo) value up to 1.41 × 106 au may be credited to the presence of loosely bound excess electrons. The hyper Rayleigh scattering hyperpolarizability (βHRS) is recorded up to 1.31 × 106 au for the K@crypt. Furthermore, frequency-dependent first-order and second-order hyperpolarizability is more prominent at the applied frequency of ω = 0.042823 au. The electron localizing function (ELF) and localized orbital locator (LOL) analysis further disclose the nature of interaction between alkali metal and complexant. The TD-DFT method is adopted to get excited state parameters and absorbance properties. An electron density difference map (EDDM) is exploited to evaluate the orbital contributions in excited states. Hence, the studied electride may become a promising candidate for NLO materials. We anticipate that the present work will provide insight into further development of molecular electride for optoelectronic applications.

MatchMaps: non-isomorphous difference maps for X-ray crystallography.

Conformational change mediates the biological functions of macromolecules. Crystallographic measurements can map these changes with extraordinary sensitivity as a function of mutations, ligands and time. A popular method for detecting structural differences between crystallographic data sets is the isomorphous difference map. These maps combine the phases of a chosen reference state with the observed changes in structure factor amplitudes to yield a map of changes in electron density. Such maps are much more sensitive to conformational change than structure refinement is, and are unbiased in the sense that observed differences do not depend on refinement of the perturbed state. However, even modest changes in unit-cell properties can render isomorphous difference maps useless. This is unnecessary. Described here is a generalized procedure for calculating observed difference maps that retains the high sensitivity to conformational change and avoids structure refinement of the perturbed state. This procedure is implemented in an open-source Python package, MatchMaps, that can be run in any software environment supporting PHENIX [Liebschner et al. (2019). Acta Cryst. D75, 861-877] and CCP4 [Agirre et al. (2023). Acta Cryst. D79, 449-461]. Worked examples show that MatchMaps 'rescues' observed difference electron-density maps for poorly isomorphous crystals, corrects artifacts in nominally isomorphous difference maps, and extends to detecting differences across copies within the asymmetric unit or across altogether different crystal forms.

KINNTREX: a neural network to unveil protein mechanisms from time-resolved X-ray crystallography.

Here, a machine-learning method based on a kinetically informed neural network (NN) is introduced. The proposed method is designed to analyze a time series of difference electron-density maps from a time-resolved X-ray crystallographic experiment. The method is named KINNTREX (kinetics-informed NN for time-resolved X-ray crystallography). To validate KINNTREX, multiple realistic scenarios were simulated with increasing levels of complexity. For the simulations, time-resolved X-ray data were generated that mimic data collected from the photocycle of the photoactive yellow protein. KINNTREX only requires the number of intermediates and approximate relaxation times (both obtained from a singular valued decomposition) and does not require an assumption of a candidate mechanism. It successfully predicts a consistent chemical kinetic mechanism, together with difference electron-density maps of the intermediates that appear during the reaction. These features make KINNTREX attractive for tackling a wide range of biomolecular questions. In addition, the versatility of KINNTREX can inspire more NN-based applications to time-resolved data from biological macromolecules obtained by other methods.

An in-depth investigation of nonlinear optical properties of self-assembled borophene doped with P7Ba2NO3: a computational simulating study

Density functional theory was used to conduct a theoretical analysis of super salt doped on borophene. With the LanL2DZ basis set, which is appropriate for metal atoms, the B3LYP technique was used. Numerous analyses were used to characterize the structural properties, such as molecular geometry, frontier molecular orbital, non-covalent interaction, electron density difference map, molecular electrostatic potential, Density of States (DOS), UV–vis spectroscopy and infrared vibrational spectra analysis. The nonlinear optical characteristics were investigated through polarizability as well as hyperpolarizability calculations theoretically. The values were noticeably greater than those of borophene in all the above results. Compared to borophene, which has a hardness value of 0.905 eV, all the complexes exhibited small values of hardness, ranging from 0.41 eV to 0.795 eV. In addition, it was found that all the complexes had lower excitation energies as opposed to the greater excitation energy of borophene. Due to its lowest excitation energy (E), Boro@SS4 showed a striking increase in average polarizability ( αo = 847.13 au) in addition average first hyperpolarizability ( β0 = 540007.60 au) in comparison to borophene ( αo = 593.75 au and β0 = 383.76 au).

Inquest for the interaction of canonical and non-canonical DNA/RNA bases with ternary based 2D Si2BN and doped Si2BN for biosensing applications

Density functional theory (DFT) is invoked to investigate the interaction between the canonical (CN) and non-canonical (NC) bases with pristine Si2BN (Si2BN) and Phosphorous-doped Si2BN (P-dop-Si2BN) sheets. Inquest for the better sensing substrate is decided through the adsorption energy calculation which reveals that doping of phosphorous atom enhances the adsorption strength of AT (-83.74 kcal/mol) AU (-82.77 kcal/mol) and GC (-96.36 kcal/mol) base pairs. The CN and NC bases have higher adsorption energy than the previous reported values which concludes that the P-dop-Si2BN sheet will be optimal substrate to sense the bases. Meanwhile, the selected CN and NC (except hypoxanthine) bases interact with sheet in parallel manner which infers the π-π interaction with Si2BN and P-dop-Si2BN sheets. The energy gap variation (ΔEg%) of the P-dop-Si2BN complexes has a noticeable change, ranging from −24.75 to −197.28% which thrust the sensitivity of the P-dop-Si2BN sheet over the detection of CN and NC bases. The natural population analysis (NPA) and electron density difference map (EDDM) confirms that charges are transferred from CN and NC bases to Si2BN and P-dop-Si2BN sheet. The optical property of the P-dop-Si2BN complexes reveals that the noticeable red and blue shift in the visible and near-infrared regions (778 nm to 1143 nm) has been observed. Therefore, the above results conclude that the P-dop-Si2BN sheet plays a potential candidate to detect the CN and NC bases which contribute to the development of biosensors and DNA/RNA sequencing devices. Communicated by Ramaswamy H. Sarma

Luminescent blue emissive bis(alkynyl) borane compounds with a N,O-coordinated ligand

Five bis(alkynyl)boranes with a (imidazo[1,5-a]pyridin-3-yl)phenolate ligand have been synthesized and characterized both in solution (1H, 13C, 11B, 19F NMR) and in the solid state (X-ray). All derivatives, differing for the substituent R (H, Me, OMe, CF3, NMe2) in the para position of the phenylacetylene moieties, displayed blue fluorescence emission in solution, linearly correlated to the electronic properties of the substituent R (i.e., its σp Hammett constant). High Stokes shifts and good quantum yields were recorded. Time-Dependent Density Functional Theory (TD-DFT) calculations were performed to describe the percentage contribution of each fragment of the molecule to the frontier orbitals. Electron Density Difference Maps (EDDMs) calculated for all derivatives allowed to explain the emissive properties of the studied compounds.

Atomic insights into the fluorinated pristine and defected graphene sheets for inducing the electronic and magnetic properties with the aid of scandium metal decoration- Acumen from density functional theory

To scrutinize the electronic and magnetic properties of fluorinated pristine, stone wales, di-vacancy, and two stone wales defected graphene sheets by scandium (Sc) metal decoration, the density functional theory is used. The obtained maximum binding and interaction energy values confirm that the two Sc metals decorated on the direct top and bottom of pentagonal rings of the two stone wales graphene sheet have stronger interactions than others. To validate the interactions, natural population analysis and electron density difference map are performed, revealing that Sc metal is the electron donor in all complexes. After the formation of defects in the pristine sheet, energy gap values are reduced in the defected sheets. The density of states infers the shift in the fermi level of all complexes after defect formation and metal decoration. The ultraviolet–visible spectral analysis exposes the highest absorption peaks of all bare sheets at the UV region and after Sc metal decoration, the peaks get red shifted. The results show that Sc metal decorated on two stone wales graphene sheet interacts better with Sc metals than other complexes. The decoration of single Sc metal in all four bare sheets transforms the sheet from a non-magnetic to a magnetic state but when two Sc metals are decorated it became non-magnetic. The highest degree of spin polarization, P = 4.15 is obtained while decorating a single Sc metal on the hexagonal ring of the pristine sheet. The outcome of this work suggests that Sc metal decoration on pristine and defected graphene sheets has great potential to improve the electronic and magnetic properties of graphene for designing spintronic and data storage devices.

Exploring the second-order polarizability of copper doped silicon carbide nanocluster: toward a new NLO material

Nonlinear optical materials are widely used in optical and optoelectronic devices. The geometric, electronic, and NLO properties of copper-doped 2D silicon carbide nanoclusters (Cu@h-SiC) are investigated. The HOMO–LUMO gap (Eg) of the h-SiC nanocluster is significantly decreased by copper atom doping. All the isomers (A to G) showed a marked drop in Eg values. It is noticed that the Eg value decreased up to 46% of the original value. The partial and total density of state graphs for all seven structures indicate the emergence of new HOMOs between the frontier molecular orbitals of h-SiC. The isomer A exhibits a significant increase in polarizability (α = 669 au) and hyperpolarizability (βo = 9.395×10−29 esu) values compared to pure h-SiC. Global reactivity descriptors (IP, EA, and S) and low excitation energies endorse the enhanced NLO response of Cu@h-SiC. The EDDM (Electron density difference map) analysis is performed to gain insight into the electronic density differences at the ground and excited levels. QTAIM analysis is used to investigate the type and nature of the interaction between the Cu-atom and the h-SiC. TD-DFT calculations predict the absorption spectra in the visible and near-IR regions. This study may help in the fabrication of h-SiC-based materials with optimised NLO response.

High-performance non-fullerene acceptor-analogues designed from dithienothiophen [3,2-b]-pyrrolobenzothiadiazole (TPBT) donor materials.

Density functional theory (DFT) method was employed to investigate the electronic structure properties, excited state dynamics, charge transfer, and photovoltaic potential of benzo [1,2,5] thiadiazole fused to 3,7-dimethyl-3a,6,7,7b-tetrahydro-5H-thieno[2',3':4,5]thieno[3,2-b]pyrrole to form 3,9,12,13-tetramethyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2″,3″:4,5]pyrrolo[3.2-g]thieno[2',3':4,5]thieno[3,2-b]indole as the acceptor (A), bridge with thiophene as π-spacer to the donor moieties (D) which are 2,3-dihydrobenzo [b]thiophene-6-carboxylic acid (M4) and functionalized R, M1, M2, M3, and M5 to give a D-π-A-π-D. Here is the reverse combination for our molecules: the A-π-D-π-A type of chromophore configuration. It is also observed that tuning the dono-bridge configuration significantly increases the ease of charge transfer as the energy gap decreases in the order of 1.29 eV in M4 < 1.59 eV in M3 < 1.67 eV < 1.99 in M2 and 2.06 eV. The reorganization energy (RE) of M3 (0.0031) and M5 (0.0031) indicates an increase in the order of M3 > M5 > R > M2 > M4 > M1. The HOMO-LUMO indicates that the reactivity decreased, while the stability increased for the reference R at 0.990 eV, compared to the designed molecules M1-M5, with M1 being the least stable at 0.970 eV, while M4 exhibited the highest stability at 1.550 eV. The stability of the designed molecule decreased in the order of M4:1.550 > M3:1.257 > M5:1.197 > M2:1.010 > M1:0.970. Therefore, all results point to the electron-deficient core as an effective end-capped electron acceptor in M1-M5 compounds. As the ideal pair for successfully optimizing optoelectronic properties by reducing the HOMO-LUMO energy levels, reorganization energy, and binding energy and enhancing the absorption maximum and open-circuit voltage values in these designed molecules. DFT and TDDFT calculations were performed with Gaussian 16 program. The modelled compounds were optimized fully using the CAM-B3LYP, WB97XD, B3LYP, and MPW1PW91 functionals with the 6-31 G (d,p) basis set. The graphs for the density of states were plotted using the PyMOlyze software. Other molecular properties like the transition density matrix (TDM) and electron density difference maps (EDD) were rendered via the Multiwfn software.

Noncovalent chemistry of xenon opens the door for anesthetic xenon recovery using Bio-MOFs.

Designing an inexpensive and highly efficient recovery process for xenon (Xe) is gaining importance in the development of sustainable applications. Using metal organic frameworks (MOFs) for separating Xe from anesthetic gas mixtures has been a recent topic studied rarely and superficially in the literature. We theoretically investigated Xe recovery performances of 43 biological MOFs (Bio-MOFs) formed by biocompatible metal cations and biological endogenous linkers. Xe uptakes and Xe permeabilities in its binary mixtures with CO2, O2, and N2 were investigated by applying Grand Canonical Monte Carlo and Molecular Dynamics simulations. Materials with metalloporphyrin, hexacarboxylate, triazine, or pyrazole ligands, dimetallic paddlewheel units, relatively large pore sizes (PLD > 5 Å and LCD > 10 Å), large void fractions (≈0.8), and large surface areas (>2900 m2 g-1) have been determined as top performing Bio-MOFs for Xe recovery. By applying Density Functional Theory simulations and generating electron density difference maps, we determined that Xe-host interactions in the top performing Bio-MOFs are maximized mainly due to noncovalent interactions of Xe, such as charge-induced dipole and aerogen-π interactions. Polarized Xe atoms in the vicinity of cations/anions as well as π systems are fingerprints of enhanced guest-host interactions. Our results show examples of rarely studied aerogen interactions that play a critical role in selective adsorption of Xe in nanoporous materials.

Outstanding performance of transition-metal decorated BC3 nanotubes for high capacity CH4 storage

In this study, dispersion-corrected density functional theory calculations are utilized to examine the possibility of storing CH4 on BC3 nanotubes (BC3NTs) decorated with Sc or Y atoms. To assess metal binding, electronic characteristics, and CH4 adsorption capability, the adsorption energies, electron density difference maps, and charge-transfer values are obtained. According to our calculations, the (8,0) BC3NT functionalized with Sc and Y atoms has a maximum gravimetric density of 21.6 and 18.9 wt% for storing CH4 molecules, respectively. The modified van't Hoff equation is used to evaluate the temperature and pressure stability of CH4 adsorbed structures. The curvature effects have been found to play an important role in the CH4 adsorption on the functionalized BC3NTs, and the BC3NTs with a large curvature are likely more suitable for storing CH4 molecules. The results suggest Sc or Y functionalized BC3NTs can be regarded as novel materials for capturing and storing of CH4 molecules at ambient temperature and pressure.

Alkaline earth metals (Be, Mg, Ca) doped hexamine complexant with enhanced electronic and nonlinear optical properties.

Organic complexant hexamine (hexamethylenetetramine, HMTA) is doped with alkaline earth (AE) metals, and new complexes are designed systematically to explore their nonlinear optical (NLO) properties by carrying out DFT calculations. Optimization of afresh designed geometries has shown their sufficient thermodynamic stability. Moreover, the energy band gap of pure HMTA is 10.62eV which is reduced up to 2.63eV for our doped complexes. This shows that alkaline earth metals are effective in enhancing the electronic properties of a system. Time-dependent DFT calculations are achieved, and results show that higher absorption maxima (λmax) along with small transition energies (ΔE) have significantly increased the hyperpolarizability (β0) values (21,338-220,585 au). This higher hyperpolarizability is an elementary prerequisite for improved NLO response of a material. Transition density matrix (TDM) analysis, density of states (DOS) analysis, and electron density difference map (EDDM) studies are executed to get information about electronic distribution, crucial transitions, and electron transfer properties. As a result of these findings, it can be concluded that alkaline earth metal-doped HMTA might be a competitor for NLO materials with remarkable optical and electronic properties and better future applications in the field of optoelectronics.

Be2C monolayer as an efficient adsorbent of toxic volatile organic compounds: theoretical investigation

In this study, the adsorption and sensing of four volatile organic compounds (VOCs) including CH2O, CH3CHO, CH2ClCHO, and C6H6 by a two-dimensional (2D) Be2C monolayer are investigated, theoretically. The adsorption of the VOCs in their isolated form and the co-adsorption of each VOC and a water molecule have also been studied, separately. The calculated adsorption energies (E ad) of the selected VOCs in the absence of the water molecule are −1.34, −0.84, −0.46, and −0.76 eV, respectively, indicating the good affinity of the Be2C monolayer for the adsorption of the VOCs. The calculated co-adsorption energies of the selected VOCs are −1.82, −0.99, −0.53, and (−0.67 and −0.82) eV, respectively. The quantum theory of atoms in molecules (QTAIM) is used to determine the interatomic interaction paths between the selected VOCs and the Be2C monolayer. The calculated natural bonding orbital (NBO) charges and the electron density difference maps of the complexes (monlayer + adsorbate) show the charge transfer from the adsorbed molecules to the Be2C monolayer except for CH2O. The potential of the Be2C monolayer for the sensing of the selected VOCs, is investigated by calculating the absorption spectra of the complexes and comparing them with the absorption spectrum of the bare Be2C monolayer.