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Cyclo[18]carbon has received considerable attention thanks to its novel geometric configuration and special electronic structure. Superalkalis have low ionization energy. Doping a superalkali in cyclo[18]carbon is an effective method to improve the optical properties of the system because considerable electron transfer occurs. In this paper, the geometry, bonding properties, electronic structure, absorption spectrum, and nonlinear optical (NLO) properties of superalkaline M 3O (M = Li, Na)-doped cyclo[18]carbon were studied by using density functional theory. M 3O and the C18 rings are not coplanar. The C18 ring still exhibits alternating long and short bonds. The charge transfer between M 3O and C18 forms stable [ M 3O]+[C18]− ionic complexes. C18 M 3O (M = Li, Na) shows striking optical nonlinearity, i.e., their first- and second-order hyperpolarizability (β vec and γ ||) increase considerably at λ = 1907 nm and 1460 nm. [ABSTRACT FROM AUTHOR]

The study of stable neutral metal endohedral cyclo[n]carbon is helpful for discovering single-molecule devices. Extensive structural search and density functional theory calculations performed here indicate that the perfect planar alkaline metal-doped complexes Sr@C 14 possess the well-defined global minima of the system with the metal atom located exactly at the center of the carbon ring. The configuration and bonding properties of C 14 are different from those of pristine cyclo [14]carbon. The significant stabilization when forming Sr@C 14 predominantly originates from the electrostatic interaction between Sr2+ and C 14 2−. The detailed molecular orbital, nucleus-independent chemical shift (NICS), and ring current analyses indicate that Sr@C 14 is aromatic in nature. The NICS values of Sr@C 14 are considerably larger than those of benzene. Ab initio molecular dynamics simulations at different temperatures reveal that this system exhibits certain stability at low or moderate temperatures. The findings of this study effectively enrich the chemical structures and bonding patterns of metal-doped cyclo[n]carbon and provide the knowledge required to obtain novel structures of Sr@C 14 in future experiments. The ground state of neutral Sr@C 14 compounds are metal-centered monocyclic carbon ring structures. Charge transfer between strontium and C 14 forms stable [Sr]2+[C 14 ]2− ionic complexes. Sr@C 14 exhibits significant aromaticity and thermodynamic stability. [Display omitted] • The ground state of neutral Sr@C 14 compounds are metal-centered monocyclic carbon ring structures. • Charge transfer between strontium and C 14 forms stable [Sr]2+[C 14 ]2− ionic complexes. • Sr@C 14 exhibits significant aromaticity and thermodynamic stability. [ABSTRACT FROM AUTHOR]

An intriguing solid-state all-carboatomic ring, cyclo[18]carbon was observed recently in experiment. In this paper, the structures, bonding characters and electronic properties of Be- and Mg-doped cyclo[18]carbon ( BeC 18 and MgC 18 ) were studied using density functional theory. The most stable structures of BeC 18 and MgC 18 are still ring-like configurations. Bond order analysis shows the characteristic of alternative bond length for the doped C 18 . Compared with primitive C 18 ring, the long C–C bond length of doped C 18 became longer and the bond order became smaller on the whole. However, the short C–C bond gets shorter and the bond order gets larger. The features of frontier molecular orbital of BeC 18 and MgC 18 were different from that of primitive C 18 . The results of bond order, electron difference density, localized orbital locator, binding energies and metal–carbon bonding interactions revealed that the structure of BeC 18 is more stable than MgC 18 . Both BeC 18 and MgC 18 are weak aromaticity. [ABSTRACT FROM AUTHOR]

Real-time monitoring of SF6 status is of exceptional importance to ensure stable operation of the power system, to promptly diagnose whether an insulation failure has occurred and to assess the severity. Considering the excellent physicochemical properties and insulation defects of hexagonal boron nitride, the strategy of surface modification, namely, hydrogenation, fluorination, and combinations of the two ways, is proposed to improve its chemical activity, and the gas-sensing potential of the most effective one is investigated using density functional theory. The typical adsorption models of SF6 decomposition component gases on the surface of F-BN-H are constructed, and the most stable adsorption structures with their density of states, molecular orbitals, and sensing responses are analyzed. The results show that F-BN-H has good sensitivity to decomposition components of SF6. To be specific, SO2 and SOF2 have good adsorption properties, prominent charge transfer, and distinct change in electronic properties. The response of gas adsorption can be detected timely by the change in conductivity, and, additionally, the adsorbent has fast desorption capacity at room temperature. These results indicate that the F-BN-H-based gas sensor is a qualified potential candidate with dependable application and recoverability for detecting SF6 decomposition in high-voltage insulated equipment. [ABSTRACT FROM AUTHOR]

[Display omitted] • The optimal adsorption configurations of deoxyribonucleic acid nucleobases and hydrogen-bonded base pairs on monolayer bismuthene are obtained according to the principle of lowest energy. • Key parameters and electronic properties of different adsorption systems are presented to get further insights of interaction mechanism for exploring potential biosensing applications. • Theoretical desorption time of single bases on bismuthene and stability of hydrogen bonds within base pairs on bismuthene are investigated. In this article, we conduct a density functional theory (DFT) investigation to reveal the adsorption characteristics of single deoxyribonucleic acid (DNA) nucleobases and hydrogen-bonded base pairs on monolayer bismuthene. The calculation results show that adenine (A), cytosine (C), guanine (G), thymine (T) interact with bismuthene in the following strength order: G > C > A > T. The magnitude of the adsorption energy is found to be 0.83 eV, 0.69 eV, 0.65 eV, 0.59 eV, respectively. These distinguishable energy levels make bismuthene a potential surface for selective detection of the four bases. During the adsorption processes, A, G, and T take charge from the adsorbent, whereas C provides charge to the adsorbent. Through electronic properties analyses, we demonstrate their physisorption essence. The key role of single oxygen atom in stronger interactions between bismuthene and C/G is also concluded. The theoretical desorption time of adsorbed G and T at 398 K are 3.21 × 10−2 s and 2.94 × 10−5 s. In addition, A-T and C-G pairs can be adsorbed on bismuthene with an adsorption energy of − 1.20 eV and − 1.26 eV. According to the detailed parameters of the pairs before and after adsorption, the hydrogen bonds between complementary bases can remain stable under the effect of bismuthene. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • B 19 Al is a nearly perfect planar, which is remarkably different from that of tubular neutral B 20 cluster. • The doped planar boron clusters can be created by doping with Al atom. • The doped planar boron clusters are essential for doped borophenes with tunable physical and chemical properties. Abstract An optimization strategy combining global semi-empirical quantum chemistry search with all-electron density functional theory was adopted to determine the lowest energy structure of B 19 Al clusters. B 19 Al is a nearly perfect planar, which is remarkably different from that of tubular neutral B 20 cluster. The Al atom occupies a peripheral position of the planar, which results from the difference in atomic size and cohesive energy between aluminum and boron atoms. Meanwhile, the planarity of B 19 Al cluster is attributed to s-p 2 hybridization. Some properties, including chemical bonding, HOMO–LUMO gaps, molecular orbital distribution, electric dipole moments, and charge transfer and distribution, are discussed. The doped planar boron clusters can be created by doping with Al atom. [ABSTRACT FROM AUTHOR]

An optimization strategy combining global semi-empirical quantum mechanical search with all-electron density functional theory was adopted to determine the lowest energy structure of (InSb) n clusters with n = 6–10. A new structural growth pattern of the clusters was observed. The lowest energy structures of (InSb) 6 and (InSb) 8 were different from that of previously reported results. Competition existed between core–shell and cage-like structures of (InSb) 8 . The structural transition of (InSb) n clusters occurred at size n = 8–9. For (InSb) 9 and (InSb) 10 clusters, core–shell structure were more energetically favorable than the cage. The corresponding electronic properties were investigated. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of alkali and alkaline-earth metal (Li, Na, K, Mg, and Ca) atom-decorated B 38 fullerene, as well as their potential for hydrogen storage, are studied using all-electron density functional theory. The metal atoms favor face-capping on top of the center of hexagonal holes of fullerene. Large binding energy prevents alkali and alkaline-earth atoms from clustering on the surface of B 38 . Large amounts of positive charges are found on Na, K, and Ca atoms. We find that calcium-coated B 38 is the best candidate for hydrogen storage, with moderate adsorption energy of H 2 . One Ca atom can adsorb up to five H 2 molecules, resulting in 20 H 2 molecules that can be stored in Ca 4 –B 38 with an average binding energy intermediate of 0.075 and 0.240 eV/H 2 . The hydrogen storage capacity reaches up to 6.47 wt.%. Charge-induced dipole interaction is responsible for the high hydrogen storage capacity of Ca 4 –B 38 . [ABSTRACT FROM AUTHOR]

[Display omitted] • The size makes cyclo[18]carbon a suitable candidate to accommodate Mg 2 molecules inside to form stable endohedral Mg 2 @C 18. • Charge transfer between Mg 2 and C 18 forms stable [Mg 2 ]2+[C 18 ]2– ionic complexes. • Large binding energy and aromaticity indicate that Mg 2 @C 18 is a remarkable stable system. The recent discovery of cyclo[18]carbon has attracted widespread attention. Density functional theory (DFT) study was carried out to evaluate the viability of the encapsulation of magnesium dimer inside the all-carboatomic ring, that is, Mg 2 @C 18. Results indicated that Mg 2 @C 18 possesses a perfect endohedral structure. Charge transfer resulted in forming typical [Mg 2 ]2+[C 18 ]2– ionic complexes. The high stability of the complex could be due to the strong electrostatic interaction between the guest Mg 2 and the host C 18 ring. The structure and bonding properties of the C 18 ring of the system is different from those of pristine cyclo[18]carbon. Mg 2 @C 18 shows remarkable aromatic character. [ABSTRACT FROM AUTHOR]

[Display omitted] • Firstly, TiO 2 -Doped GeSe Monolayer are studied. • The introduction of dopants improves the selectivity and sensitivity of GeSe. • Doped GeSe have suitable sensing traits to perfect adsorption and desorption. • The change of conductivity is critical to production of resistive gas sensors. The detection of SF 6 decomposition species has been a crucial method of fault diagnosis for insulation equipment. Faced with problems of poor selectivity, low sensitivity and non-recyclability of existing nano-gas sensors, TiO 2 -doped GeSe monolayer is proposed. The doping of TiO 2 nanoparticle greatly improves the conductivity of GeSe monolayer and the selective for SF 6 decomposition species, SO 2 > H 2 S > SOF 2 > SO 2 F 2. Moreover, electron transfer of SF 6 is further inhibited. When gases are adsorbed, the reduction of the difficulty of electron transition ensures the high sensitivity detection in practical application, especially SO 2. Ideal adsorption energies ensure that TiO 2 -GeSe monolayer has excellent response and recovery ability, which theoretically solves the industrial problem of recycling. In addition, compared with pure GeSe and other normal 2D materials, TiO 2 -GeSe exhibits excellent sensing detection advantages. This study provides a theoretical foundation for resistive chemical sensors used in industrial insulation equipment. [ABSTRACT FROM AUTHOR]

Compared with MoS 2 monolayer, the SV-MoS 2 monolayer improves the absorbability toward SF 6 decomposition products and increases the selectivity of SO 2 F 2. [Display omitted] • The investigation about sulfuric vacancy in two-dimensional molybdenum disulfide monolayer. • The adsorption behavior of typical SF 6 decomposition components on SV-MoS 2 monolayer is shown. • The physical sensing properties and mechanism of adsorption system are fully analyzed. A long-running SF 6 insulating gas decomposes without being detected in time would cause incalculable consequences, therefore, real-time monitoring towards SF 6 status is of practical significance. Currently, the gas-sensitive properties of two-dimensional materials are the focus and hotspot of gas sensor research, however, in practical situations, material preparation and device fabrication will inevitably bring about defects. Therefore, the effects of sulfuric vacancy (SV) in molybdenum disulphide are proposed and explored, and a comparative study of gas-sensitive properties (pristine MoS 2 vs SV- MoS 2) is carried out using density functional theory based on the first principles. Constructing typical adsorption models for SF 6 decomposition components on monolayer, together with analyzing the optimum adsorption structures, adsorption energy, density of states, molecular orbitals, electrical conductivity and co-adsorption behaviors. The results show that the SV brings a defective state to MoS 2 monolayer, which contributes to an overall increase in the adsorption energy for the decomposition components (the increase > 0.15 eV), making the undifferentiated adsorption effect selective for SO 2 F 2. The physical interaction between the decomposition products and SV-MoS 2 monolayer is more favorable for desorption. These results indicate it is appropriate for detecting SF 6 status in high-voltage insulation environments, with pointers to practical applications for two-dimensional materials. [ABSTRACT FROM AUTHOR]

The C 3 N/h-BN is a narrow-gap semiconductor and has uniquely E-field/strain dependent and highly adjustable electronic properties. The band gap of C 3 N/h-BN heterostructure is sensitive to the strain, and keeps its semiconductor characteristics with a linear and highly controllable change rule. Electric fields can be effectively used to keep semiconductor or metal state steadily within a specified range of electric fields, suggesting a broad prospect in the area of electronic devices, such as switching devices, data storage devices. [Display omitted] • The C 3 N is bonded to the h-BN monolayer via weak vdW forces. • The band gap of the heterostructure is linearly positive-correlated with strain. • The E-field could make the heterostructure change from semiconductor to metal. • The semiconductor or metal state can be kept stable within a defined E-field range. Heterostructures are widely used in 2D material-based semiconductor industry because of their effective regulation toward certain materials for desirable performance. In this work, we have comprehensively investigated the structural and electronic properties of the C 3 N/h-BN heterostructure by means of density functional theory. Obtained results show that the proposed heterostructure is a narrow-gap semiconductor and it also has uniquely E-field/strain dependent relationship and highly adjustable peculiarity. More specifically, its band gap structure shows different trends under external E-field and strain, which shows up remarkable capability and favorable applicability in the field of semiconductor band gap engineering. [ABSTRACT FROM AUTHOR]

• The Rh-doping behavior on BN monolayer has a good doping effect. • Rh-BN monolayer exhibits ideal adsorption and sensing properties, selectivity for SF 6 decomposed gases. • The electronic behavior and sensitivity analysis help to understand mechanism and reflect the excellent applicability. The SF 6 decomposed gases sensor is crucial for detecting insulation condition of electrical equipment. To study applicability of metal-doped two-dimensional (2D) nanomaterials for gas sensors, density functional theory (DFT) calculations based on first-principle theory were used for investigating adsorption properties, sensitivity and electronic behavior. In this study, Rh-doped h-BN (Rh-BN) monolayer was first proposed to analyze adsorption of typical SF 6 decomposed gases, including H 2 S, SO 2 , SOF 2 , SO 2 F 2. The stable structure of Rh-BN monolayer was studied by four possible sites. The binding energy (E b) of stable structure is −1.204 eV. Meanwhile, the adsorption energy (E ad) and sensitivity of SF 6 decomposed gases show that Rh-BN monolayer has ideal adsorption and sensing properties than other materials. Moreover, the analysis of density of state (DOS) and band structure illustrate the sensing mechanism and further prove the applicability of Rh-BN monolayer for SF 6 decomposed gases. The above calculations and analysis would be significant to explore Rh-BN monolayer as a novel SF 6 decomposed gases sensor for electrical equipment insulation. [ABSTRACT FROM AUTHOR]