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Calcium-sensing receptor (CaSR), which was initially found in the parathyroid gland, is ubiquitously expressed and exerts specific functions in multiple cells, including immune cells. CaSR is functionally expressed on neutrophils, monocytes/macrophages, and T lymphocytes, but not B lymphocytes, and regulates cell functions, such as cytokine secretion, chemotaxis, phenotype switching, and ligand delivery. In these immune cells, CaSR is involved in the development of many diseases, such as sepsis, cryopyrin-associated periodic syndromes, rheumatism, myocardial infarction, diabetes, and peripheral artery disease. Since its discovery, it has been controversial whether CaSR is expressed and plays a role in immune cells. This article reviews current knowledge of the role of CaSR in immune cells.

The electroreduction of CO (COER) to valuable carbon-based chemicals is an attractive alternative to the traditional Fischer–Tropsch process, in which the development of electrocatalysts with high activity and high selectivity still remains a huge challenge. Herein, by means of density functional theory (DFT) computations, we systematically explored the potential of defective MoS2 monolayers with sulfur vacancies, including mono-sulfur (VS), di-sulfur (VS2 and V2S), and tri-sulfur (V3S), as COER electrocatalysts. Our results revealed that these defective MoS2-based candidates exhibit low formation energies and high stability, holding great promise for experimental synthesis and practical applications. In particular, according to the computed free energy changes, we found that the catalytic activity of these considered defective MoS2 monolayers for COER is highly dependent on the size of sulfur vacancies in MoS2 monolayers, among which V3S exhibits the best COER catalytic performance, and CH4 is identified as the main product. Interestingly, the difference between the adsorption strength of *CH2 and *CH3 species can be used as a rational descriptor to evaluate the COER catalytic activity of these defective MoS2 monolayers. Thus, controlling the size of S-vacancies can make MoS2 monolayers a promising electrocatalyst for COER, which not only further widens the potential of MoS2 monolayers in electrocatalysis, but also opens a new door for CO reduction for renewable energy supply.

The electrochemical reduction of nitrobenzene (NBER) holds great promise for not only removing toxic pollutants, but also producing valuable aniline, in which the development of catalysts with high-efficiency still remains a huge challenge. In this work, by means of density functional theory (DFT) computations, we proposed several single transition metal (TM) atoms embedded into the single vacancy of graphene with nitrogen-doping (TMN3/G, TM = Ni, Cu, Pd, and Pt) as the catalysts for NBER. Our results revealed that, among these candidates, PtN3/G is the most active catalyst for the NBER due to its smallest limiting potential (-0.21 V), in which the hydrogenation of Ph-NO2* to Ph-NOOH* is identified as the potential-determining step. Compared with other catalysts, the strongest binding strength of Ph-NOOH* with PtN3/G is responsible for its superior catalytic activity towards NBER, which can be deeply understood on the basis of the corresponding electronic structure analysis. Thus, PtN3/G is a quite promising single-atom-catalyst with high efficiency for nitrobenzene reduction, which provides a rational paradigm for converting harmful nitrobenzene to valuable aniline under ambient conditions.

Developing highly efficient electrocatalysts for multiple electrode reactions is of great importance for the large-scale applications of some energy conversion and storage devices. In this work, by means of spin-polarized density functional theory (DFT) computations, we have systematically explored the catalytic performance of several palladium (Pdn, n = 1–6, and 13) nanoclusters anchored on the experimentally available defective MoS2 monolayer with S monovacancy (Pdn/MoS2) for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Our results revealed that these studied Pdn/MoS2 materials have high stability due to the strong interaction of Pd clusters with the dangling Mo atoms and the S atoms around the vacancy with the binding energy per Pd atom ranging from −3.12 to −4.36 eV. Interestingly, the ORR/OER catalytic activity of these Pdn/MoS2 catalysts was greatly dependent on the sizes of the anchored Pd clusters: Pd6/MoS2 is predicted to exhibit the highest ORR catalytic activity due to its lowest overpotential of 0.59 V among all the studied catalysts, while Pd2/MoS2 is identified as the best OER catalyst due to its ultra-low overpotential of 0.32 V. Thus, our DFT results suggested that the ORR/OER catalytic performance could be effectively tuned by precisely controlling the sizes of the anchored Pd clusters on the MoS2 monolayer, which provides an important insight to further design novel and efficient ORR/OER catalysts.

The electrochemical reduction of nitrogen (NRR) at ambient conditions is an appealing alternative to the industrial method for ammonia synthesis that requires high temperature and pressure, but its efficiency is greatly dependent on stable and efficient electrocatalysts. Hence, by means of comprehensive density functional theory (DFT) computations, we investigated the potential of a new class of metal-organic frameworks (MOF)-based catalyst for the NRR, namely, the synthesized π-conjugated metal bis(dithiolene) nanosheet (MC4S4, M = Fe, Co, Ni, Ru, Rh, Pd, Pt, Os, and Ir). Our results demonstrated that the NRR catalytic activity of MC4S4 is highly dependent on the central metal atom. Due to the low overpotential (0.31 V), the OsC4S4 nanosheet is predicted to exhibit outstanding NRR catalytic activity through the distal mechanism, in which the hydrogenation of the activated N2 molecule to the N2H* species is identified as the potential-determining step. Our work is the first report of 2D MOF-based electrocatalyst for N2 reduction, opening a new avenue for advancing sustainable NH3 synthesis under ambient conditions.

OBJECTIVES This study aimed to determine ultrasonic image characteristics that enable differentiation between cholesterol and adenomatous polyps and to assess the diagnostic efficacy of combining conventional ultrasound (CUS) with contrast-enhanced ultrasound (CEUS). METHODS Eighty-nine patients with gallbladder polyps of 1-2 cm in diameter were enrolled and examined by CUS and CEUS before cholecystectomy. The appearances on CUS and CEUS were recorded and analyzed. The receiver operating characteristic (ROC) curve was used to calculate the optimal size threshold for distinguishing cholesterol from adenomatous polyps. A logistic regression analysis was performed to identify diagnostic variables. ROC analysis was performed to evaluate the diagnostic efficacy of the size, the independent variables, and the combined factors. RESULTS There were differences in size, number, vascularity on CUS and intralesional vascular shape, wash-out, and area under the curve on CEUS between the two groups (P

Introducing heteroatoms into two-dimensional nanosheets was revealed to be a quite promising strategy to tune their electronic and magnetic properties as well as chemical reactivity, thus greatly widening their application fields. Herein, by means of density functional theory (DFT) computations, we have systematically investigated the electronic and magnetic properties as well as chemical reactivity of MoS2 nanosheets doped with several common nonmetal dopants (B, C, N, O, and P). Our results revealed that these nonmetal atoms can be strongly captured by the S vacancy of the MoS2 nanosheet, ensuring their high stability. Compared with the pristine MoS2 nanosheet, these doped MoS2 systems exhibit decreased band gaps due to the introduction of impurity levels. In particular, the adsorption of gas molecules on the MoS2 monolayer can be enhanced to different degrees after nonmetal doping, suggesting great potential for developing gas sensors or catalysts. Thus, by carefully choosing the nonmetal atoms, the inert basal plane of a MoS2 nanosheet can be effectively activated for various applications.

Searching for effective anchoring material to capture and convert lithium polysulfides (Li2Sn ) for suppressing their shuttling effects has been a key scientific issue for the development of lithium sulfur (Li–S) batteries with high-efficiency. Herein, by means of density functional theory (DFT) computations, we have explored the potential of doped MoS 2 monolayers with a series of metal atoms in place of Mo or S atom as the anchoring materials for Li–S batteries. Our results revealed that Li2Sn species can be physisorbed on doped MoS2 monolayer by substituting Mo atom with metal dopant , inducing a limited enhancement for the immobilization of Li 2Sn species, as compared with pristine MoS2 monolayer. In contrast, due to the synergistic effects between metal dopant and its adjacent S atoms, the substitution in S atom with metal dopant greatly improves the binding strength of Li2Sn species on MoS2 monolayer, particularly saving the intact Li2Sn configuration. More interestingly, this kind of metal-doped MoS2 monolayer exhibits good catalytic activity for the formation and the decomposition of Li2S in discharge and charge processes. Thus, metal-doped MoS2 monolayers can be utilized as the multifunctional anchoring materials for Li–S batteries by carefully controlling the kinds and sites of dopants in MoS2 monolayer, which opens up a new strategy to further develop high-performance Li–S batteries.

Searching for metal-free catalysts for the carbon dioxide reduction reaction (CO2RR) has been a key challenge in the electrosynthesis of fuels for CO2 utilization. In this work, we investigated the potential of N-doped graphene as the electrocatalyst of CO2RR by means of comprehensive density functional theory (DFT) computations. The computations revealed that N-doping can modify the electronic properties of graphene for enhancing the electrochemical reduction of CO2 into CO and HCOOH, resulting in a low free energy barrier for the potential-limiting step to form the key intermediate COOH as well as the strong adsorption energy of adsorbed COOH and the weak adsorption energy of CO or HCOOH. The highest catalytic activity toward CO2RR is shown by pyrrolic N-doped graphene due to its lowest overpotential of 0.24 V among all N-doped graphenes, and leads exclusively to HCOOH as the product. Therefore, our results demonstrated that N-doped graphene holds great promise as an electrocatalyst for the CO2RR with high efficiency and selectivity by suitably tuning its N species.

Development of low-cost and highly efficient electrocatalysts for oxygen reduction reaction (ORR) is still a great challenge for the large-scale application of fuel cells and metal–air batteries. In this work, by means of density functional theory (DFT) computations, we have systemically explored the anchoring of Co(acac)2 (acac = acetylacetonate) on N-doped graphene nanoribbon and its potential as the ORR electrocatalyst. Our DFT computations revealed that N-doped graphene nanoribbon can be used as the anchoring material of the Co(acac)2 complex due to the formation of a Co–O4–N moiety, thus ensuring its high stability. Especially, an O2 molecule can be moderately activated on the surface of the anchored Co(acac)2 complex, and the subsequent ORR steps prefer to proceed though a more efficient 4e pathway with a small overpotential (0.67 V). Therefore, the hybridization of Co(acac)2 with N-doped graphene can give rise to outstanding catalytic performance for ORR in fuel cells.

Recent studies have suggested that chemical functionalization is a promising avenue to tailor the band gap of silicene, which plays an important role on widening its application. Here, we propose a new route to functionalize silicene, that is asymmetrically modification of silicene (Janus silicene or X –silicene– Y ), which is produced by co-grafting of two different groups ( X and Y ) on both sides of silicene. By performing density functional theory (DFT) calculations, we demonstrate the stability and electronic properties of X –silicene– Y sheets. The results indicate that chemical functionalization on one side can greatly enhance the chemical reactivity of the opposite side, suggesting the communication between the two adsorbed groups and enhancing the stability of the hybrids. Compared to the pristine silicene with a zero band gap, X –silicene– Y sheets exhibit semiconducting nature with a non-zero band gap, which is dependent on the coverage of X / Y . Our results provide a novel and effective method to engineer the band gap of silicene, which would be useful to design novel silicene-based devices with multiple functions.

We performed comprehensive density functional theory (DFT) calculations to explore the possibility of the Fe-embedded hexagonal boron nitride ( h -BN) sheet as a novel electrocatalyst for ORR. Our results show that Fe atom can strongly bind with defective BN sheet and thus ensure its high stability. Moreover, O 2 molecule is found to be strongly chemisorbed on Fe-embedded BN sheet with the adsorption energy of −1.76 eV, which can server as precursors for ORR, followed by its hydrogenation into OOH species rather than direct breakage of the O–O bond. Further, the HOOH species in the process of OOH reduction is shown to be unstable and dissociates into two OH group, suggesting that ORR catalyzed by Fe-embedded BN sheet is a direct four-electron pathway. Finally, on the basis of the calculations on the free energy change and activate energy of each step in ORR, we expect that Fe-embedded BN sheet exhibits good catalytic activity for ORR. Our results provide an useful guidance for the design and fabrication of novel and nonprecious BN sheet-based electrocatalyst for ORR as the alternative of expensive Pt catalysts.

Recently, the Si/graphene hybrid composites have attracted considerable attention due to their potential application for Li-ion batteries. How to effectively anchor Si clusters to graphene substrates to ensure their stability is an important factor to determine their performance for Li-ion batteries. In the present work, we have performed comprehensive density functional theory (DFT) calculations to investigate the geometric structures, stability, and electronic properties of the deposited Si clusters on defective graphenes as well as their potential applications for Li-ion batteries. The results indicate that the interfacial bonding between these Si clusters with the pristine graphene is quietly weak with a small adsorption energy (

Recently, the encapsulation of various species inside boron nitride nanotubes (BNNTs) was identified as an effective method for modifying the physical and chemical properties of boron nitride nanotubes (BNNTs), thus greatly widening their potential applications. In the present work, we have performed comprehensive density functional theory (DFT) calculations to study the effects of the encapsulation of various numbers of Li atoms on the electronic and magnetic properties of a BNNT. The results show that two, three, and four Li atoms can be stably encapsulated inside a BNNT (Eint = −1.198, −2.081, and −2.378 eV, respectively), giving interaction energies that are much larger than that of one Li atom (Eint = −0.052). Because a certain number of electrons are transferred from these encapsulated Li atoms to the BNNT, some impurity levels are induced within the band structures of the BNNT, thus reducing its band gap. Encapsulation of three and four Li atoms renders the BNNT a metallic material, whereas 2Li@BNN...

The properties and reactivity of Si-doped hexagonal boron nitride (h-BN) sheets were studied using density functional theory (DFT) methods. We find that Si impurity is more likely to substitute the boron site (SiB) due to the low formation energy. Si-doping severely deforms h-BN sheet, resulting in the local curvature changes of h-BN sheet. Moreover, Si-doping introduces two spin localized states within the band gap of h-BN sheet, thus rendering the two doped systems exhibit acceptor properties. The band gap of h-BN sheet is reduced from ∼ 4.70 eV to 1.24 (for SiB) and 0.84 eV (for SiN), respectively. In addition, Si-doped one exhibits higher activity than pristine one, endowing them wider application potential.

The pristine boron nitride nanotube (BNNT) exhibits a poor chemical reactivity to some adsorbates, thus greatly limiting its application for the gas sensor. In the present work, using density functional theory (DFT) methods, we put forward a novel strategy to enhance the sensitivity of BNNT to nitrogen dioxide (NO2) by the encapsulation of a single Fe atom inside its cavity. The results suggest that the NO2 molecule can be only physically adsorbed on the pristine BNNT with a small adsorption energy (-0.10 eV). After the inclusion of the Fe atom inside BNNT (Fe@BNNT), the interaction of NO2 molecules with this tube is significantly enhanced, leading to a transformation from the physisorption of on pristine BNNT to the current chemisorption. Interestingly, up to five NO2 molecules can be adsorbed on this encapsulated BNNT along its circumference with the average adsorption energy of -0.52 eV, corresponding to a short recovery time (6 ms). Moreover, 0.38 electrons are transferred from the Fe@BNNT to the adsorbed NO2 molecules, which is enough to induce the obvious change of its electrical conductance. Thus, we predict that the encapsulation of Fe atom inside BNNT would greatly boosts its sensitivity to NO2 molecules, indicating its potential application as NO2 sensors.

—The main research contents in this paper are as following. Building a test bench for engine heat balance, and completed the test equipment and debug engine. Through test we can obtain the coolant pressure characteristic curve, temperature characteristic curve and flow rate characteristic curve in different working conditions. Researched the engine heat distribution laws and influencing factors based on the engine coolant temperature in the engine full-load characteristic conditions.

Recent studies have shown that two-dimensional nanomaterials can serve as excellent candidates for the support of metal nanoparticles, thus rendering them to have potential applications for developing novel electrocatalysts in the oxygen reduction reaction (ORR). In this work, by performing density functional theory calculations, we investigate the structural and electronic properties of Pt clusters deposited on several defective hexagonal boron nitride (h-BN) sheets as well as their interaction with O that is closely related to the electrocatalytic activity of these composites in ORR. As compared with the pristine h-BN sheet, we find that the binding strength of Pt clusters on defective h-BN sheets is significantly enhanced, which is attributed to their strong hybridization with the sp2 dangling bonds at the vacancy site. Thus, the point defect on h-BN sheets plays a key role on anchoring Pt clusters, ensuring their high stability. More importantly, the interfacial interaction can effectively modify the ...

In the present work, we have investigated the stable configurations, electronic, and magnetic properties of the functionalized boron nitride (BN) nanosheets by NH x (x = 0, 1, and 2) groups by performing comprehensive density functional theory (DFT) calculations. The results indicate that these groups can be stably incorporated into BN nanosheet, resulting in the formation of covalent bonds between these adsorbates and BN sheet. The adsorption energies of the most stable configurations are − 2.80, − 2.42, and − 0.33 eV, respectively, for the adsorption of N, NH, and NH 2 groups on BN nanosheet. The electronic structures of BN nanosheets are found to be effectively modified by these groups due to the introduction of certain impurity states within the band gap of the pristine BN nanosheet, thereby reducing the band gaps in various ways. The relationship between the electronic structures and the configurations of these functionalized BN nanosheets is also addressed by exploring the projected density of states combined with charge transfer analysis. In particular, the attachment of the N and NH 2 groups renders BN nanosheet to exhibit magnetic nonzero magnetic moment, contributed mainly by the N atoms of adsorbates. The present results are expected to open a way to change the electronic and magnetic properties of BN nanosheet, which is helpful to design or develop novel nanodevices based on BN nanosheet.

It is well known that pristine hexagonal boron nitride sheet ( h -BN sheet) exhibits large insulating band gap, thus hindering its application to some extent. In this regard, surface chemisorption of certain groups on h -BN sheet is shown to be the most popular method to tune its band gap and thus modify its electronic properties. In the present work, we performed density functional theory (DFT) calculations to study the adsorption of CHO radicals with different coverages on h -BN sheet. Particular attention is paid to explore the effects of CHO adsorption on the geometrical structures and electronic properties of h -BN sheet. The results indicate that the adsorption of a single CHO radical on pristine h -BN sheet is very weak with a negligible adsorption energy (−0.09 eV). In contrast, upon adsorption of more CHO radicals on h -BN sheet, these adsorbates prefer to adsorb in pairs on the B and the nearest N atoms from both sides of h -BN sheet. An energy diagram of the average adsorption energy of CHO radicals on h -BN sheet as a function of its coverage indicates that up to 20 CHO radicals (40%) can be attached to h -BN sheet with the adsorption energy of −0.29 eV. More importantly, the adsorption of CHO radicals can induce certain impurity states within the band gap of h -BN sheet, thus reducing the band gap and enhancing its electrical conductivity.

Motivated by the great advance in graphene hydroxide--a versatile material with various applications--we performed density functional theory (DFT) calculations to study the functionalization of the two-dimensional hexagonal boron nitride (h-BN) sheet with hydroxyl (OH) radicals, which has been achieved experimentally recently. Particular attention was paid to searching for the most favorable site(s) for the adsorbed OH radicals on a h-BN sheet and addressing the roles of OH radical coverage on the stability and properties of functionalized h-BN sheet. The results indicate that, for an individual OH radica, the most stable configuration is that it is adsorbed on the B site of the h-BN surface with an adsorption energy of -0.88 eV and a magnetic moment of 1.00 μ(B). Upon adsorption of more than one OH radical on a h-BN sheet, however, these adsorbates prefer to adsorb in pairs on the B and its nearest N atoms from both sides of h-BN sheet without magnetic moment. An energy diagram of the average adsorption energy of OH radicals on h-BN sheet as a function of its coverage indicates that when the OH radical coverage reaches to 60 %, the functionalized h-BN sheet is the most stable among all studied configurations. More importantly, this configuration exhibits good thermal and dynamical stability at room temperature. Owing to the introduction of certain impurity levels, the band gap of h-BN sheet gradually decreases with increasing OH coverage, thereby enhancing its electrical conductivity.

Density functional theory (DFT) calculations were performed on the NO reduction on the silicon (Si)-doped graphene. The results showed that monomeric NO dissociation is subject to a high barrier and large endothermicity and thus is unlikely to occur. In contrast, it was found that NO can easily be converted into N2O through a dimer mechanism. In this process, a two-step mechanism was identified: (i) the coupling of two NO molecules into a (NO)2 dimer, followed by (ii) the dissociation of (NO)2 dimer into N2O + O(ad). In the energetically most favorable pathway, the trans-(NO)2 dimer was shown to be a necessary intermediate with a total energy barrier of 0.464 eV. The catalytic reactivity of Si-doped graphene to NO reduction was interpreted on the basis of the projected density of states and charge transfer.

Recently, doping non-carbon atoms into graphene or carbon nanotube (CNT) has attracted considerable attention due to its effectiveness to change or tailor their electronic and magnetic properties as well as chemical reactivity. In this work, we present a density functional theory study of the recently synthesized phosphorus (P) doped graphene and CNT. Particular attention is paid to studying the effects of P-doping on the structural, electronic, and magnetic properties as well as chemical reactivity of graphene or CNT. The results show that P dopant drastically changes the geometrical structure of graphene or CNT, rendering P and its neighboring C atoms protrude from the sidewall of CNT and graphene. Moreover, P-doping induces localized electronic states into graphene and CNTs, thus modifying the electronic properties by producing n-type behavior. Meanwhile, due to P doping, the graphene and CNT exhibit magnetic nature with spin net moment of 1.02 and 0.99 μB, respectively. In order to evaluate the chemical reactivity of the two nanostructures, their interactions with several gas molecules, including NH3, H2O, O2, NO2, and NO, are further calculated. Our results may be useful not only for deeply understanding the properties of CNTs and graphenes, but also for developing various novel nanodevices.

Recently, the adsorption and dissociation of oxygen molecule on a metal-free catalyst has attracted considerable attention due to the fundamental and industrial importance. In the present work, we have investigated the adsorption and dissociation of O(2) molecule on pristine and silicon-doped graphene, using density functional theory calculations. We found that O(2) is firstly adsorbed on Si-doped graphene by [2+1] or [2+2] cycloaddition, with adsorption energies of -1.439 and -0.856eV, respectively. Following this, the molecularly adsorbed O(2) can be dissociated in different pathways. In the most favorable reaction path, the dissociation barrier of adsorbed O(2) is significantly reduced from 3.180 to 0.206eV due to the doping of silicon into graphene. Our results may be useful to further develop effective metal-free catalysts for the oxygen reduction reactions (ORRs), thus greatly widening the potential applications of graphene.

Chemical functionalization of the boron nitride nanotube (BNNT) allows a wider flexibility in engineering its electronic and magnetic properties as well as chemical reactivity, thus making it have potential applications in many fields. In the present work, the encapsulation of 13 different Pd(3)M (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Pt, and Au) clusters inside the (10, 0) BNNT has been studied by performing comprehensive density functional theory (DFT) calculations. Particular attention is paid to searching for the stable configurations, calculating the corresponding binding energies, and evaluating the effects of the encapsulation of Pd(3)M cluster on the electronic and magnetic properties of BNNT. The results indicate that all the studied Pd(3)M clusters can be stably encapsulated inside the (10, 0) BNNT, with binding energies ranging from -0.96 (for Pd(3)Sc) to -5.31 eV (for Pd(3)V). Moreover, due to a certain amount of charge transfer from Pd(3)M clusters to BNNT, certain impurity states are induced within the band gap of pristine BNNT, leading to the reduction of the band gap in various ways. Most Pd(3)M@BNNT nanocomposites exhibit nonzero magnetic moments, which mainly originate from the contribution of the Pd(3)M clusters. In particular, the adsorption of O(2) molecule on BNNT is greatly enhanced due to Pd(3)M encapsulation. The elongation of O-O bonds of the adsorbed O(2) molecules indicates that Pd(3)M@BNNT could be used to fabricate the oxidative catalysis.

The diazomethyl (HCNN) radical has attracted considerable attention due to its great interest in interstellar chemistry and combustion processes. In this article, we have systemically studied the low-lying electronic states of the HCNN radical and its ions through complete active space self-consistent field and multiconfigurational second-order perturbation theory. For the ground state of HCNN, the calculated CH stretch ν1, asymmetric NNC stretch ν2, and NCH bend ν4 are 3305, 1876, and 870 cm−1, respectively. The ν4 is close to the experimental value of 871 cm−1. The adiabatic excitation energies of 12A′ and 22A″ of HCNN are shown to be in agreement with the experimental reports. Moreover, the first adiabatic detachment energy of HCNN− is 1.628 eV, which accords with the experimental value of 1.685 ± 0.006 eV. Our work might not only be helpful for deeply understanding the character of the low-lying electronic states of the HCNN radical and its ions, but also provide a theoretical guidance for further studying the photoelectron spectrum of HCNN and HCNN−.

Electronic states of the CH(3)Se and its cation CH(3)Se(+) have been studied using the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the ANO-RCC(TZP) basis set. To investigate the Jahn-Teller effect on the CH(3)Se radical, C(s) symmetry was used for CH(3)Se in calculations. The results show that the Jahn-Teller effect is very small (69 cm(-1)) and the 1(2)A' state is slightly more stable than the 1(2)A'' state (8 cm(-1)). The CH(3)Se has been found to have a 1(2)A' ground state with a C-Se bond distance of 1.975 A. The computed C-Se stretching nu(6)(a') frequency is 554.1 cm(-1), which is in good agreement with the experimental values of 600 +/- 60 cm(-1). The calculations for CH(3)Se at 3.621 and 5.307 eV are attributed to 1(2)A' --2(2)A'(1(2)A(1)) and 1(2)A' --2(2)A'', respectively. The vertical and adiabatic ionization energies were obtained to compare with the PES data.

The AlCCH radical is a photolysis product of the aluminum-acetylene adducts and has been considered as a molecule with potential interest in astrophysics. In this study, the low-lying electronic states of the AlCCH radical, cation, and anion have been studied by using complete active space self-consistent field and multiconfigurational second-order perturbation theory. The geometrical parameters, electron configurations, excitation energies, oscillator strengths, and harmonic vibrational frequencies are calculated in C(S) symmetry. For the X(1)Sigma(+) state of AlCCH, the calculated C-C and C-Al stretching modes are in good agreement with experimental reports. Moreover, the vertical excitation energy (T(v)) of 1(1)Pi is 3.68 eV, which is close to the experimental value of 3.57 eV. The electron transitions of AlCCH(+), X(2)Sigma(+) --> 1(2)Pi, X(2)Sigma(+) --> 2(2)Sigma(+), and X(2)Sigma(+) --> 1(2)Sigma(-), are predicted at 2.57, 4.51, and 4.61 eV, respectively. For AlCCH(-), the transition X(2)Pi --> 1(2)Sigma(-) occurs at 3.02 eV. The ionization potentials of AlCCH are computed in order to provide a theoretical guidance to the photoelectron spectrum of the AlCCH radical.

The complete active space self-consistent field and multiconfigurational second-order perturbation theory methods have been used to investigate the low-lying electronic states of the HCCO radical and its anion. The calculated geometrical structure and harmonic vibrational frequencies for the X 2A″ state of HCCO are in good agreement with experimental values. The barrier to 12П (12A′) is estimated to be 0.069 eV (554 cm−1), which is also close to experimental result (540 cm−1). Moreover, we find that the 22A′ state is bent, while 22П (22A″) is linear. By comparing the oscillator strengths and adiabatic excitation energies, we show that the 22П (22A″) ← X 2A″ transition is the most intense among these transitions. The unpaired electrons mainly locate on the C atoms in the 22A′ and 22П (22A″) states according to the Mulliken spin populations. On the other hand, for HCCO−, the first adiabatic and vertical detachment energies are 2.210 and 2.362 eV, respectively, which reasonably agree with experimental value of 2.338 ± 0.008 eV. Remarkably, we explore several higher excited states of the HCCO radical (14A′, 24A″ and cis-14A′) and its anion (13A″, 11A″ and 13A′), which have not been reported in previous studies.

Encouraged by the great promise of metal–nitrogen–carbon (M–N–C) materials in replacing Pt for catalyzing the oxygen reduction reaction (ORR), metal–P species were successfully introduced into carbon matrices in experiments and have exhibited high catalytic activity for the ORR. Here, by means of comprehensive density functional theory (DFT) computations, we investigated the origin and the mechanism of the ORR occurring on Fe– and Co–P-embedded graphenes. Our computations have revealed that the Fe– and Co–P4 moiety-embedded graphenes possess good stability and high chemical reactivity for O2 activation, thus facilitating the subsequent ORR steps, and a more efficient 4e pathway in both acidic and alkaline media is more energetically favorable. Furthermore, by analyzing the computed free energy profiles, the Fe–P4 species-embedded graphene is a more efficient electrocatalyst for the ORR in an alkaline medium than the Co–P4 species-embedded graphene. Our DFT computations will be useful for gaining deeper insight into the high activity of metal–P species.

Healing defects in hexagonal boron nitride (h-BN sheet) or doping it with oxygen can modify or restore its physical properties, which would increase its range of potential applications. Thus, it is very important to find an efficient method of healing or a BN sheet or doping it with oxygen. In this work, using density functional theory (DFT) calculations, we identified a mechanism for healing h-BN sheets with nitrogen vacancies (VN) or doping BN sheets with oxygen using NO2 molecules. The results indicate that such reactions involve three steps: (1) the chemisorption of NO2, (2) the incorporation of the N or O atom of NO2 into the defective h-BN sheet, and (3) the removal of the adsorbed O atom or NO molecule. We found that the proposed mechanism is theoretically possible and has the following advantages. First, the barrier is about 0.60 eV for the formation of the O-doped h-BN sheet. For the healing process, because the energy released during NO2 chemisorption (-4.94 eV) completely offsets the subsequent barrier (1.17 eV), a perfect h-BN sheet can easily be achieved by using NO2 and an h-BN sheet with VB defects as reactants. Second, no catalyst is needed, and thus there is no need for a purification step to remove the catalyst. Third, NO2, a toxic gas, can be used as a reactant and will then be reduced to O2 or NO. Fourth, NO2 shows high selectivity for vacancy defect sites. Our findings show that this is an effective theoretical method of synthesizing O-doped h-BN sheets or of healing defective h-BN sheets, which should prove useful in the design of h-BN sheet-based devices.

Controllable carbon (C) doping in a boron nitride (BN) nanostructure can render it exciting magnetic and conductive properties, which would be very valuable for its potential applications in optoelectronics and spintronics. Thus, searching for an efficient method to achieve C-doped BN nanostructure is of vital importance. Here, using density functional theory (DFT) calculations, we propose a mechanism to obtain C-doping of BN nanosheet by the interactions of two CO molecules with three kinds of defective BN nanosheets, including B or N vacancy and BN divacancy. The results show that the proposed mechanism in the present work has the following advantages: (i) the activation energies are only 0.30 and 0.37 eV for BN sheet with B and N vacancy, respectively, suggesting that this reaction can easily occur. For BN sheet divacancy configuration, because the released energy of CO-coadsorption (−5.49 eV) can completely offset the subsequent barrier (1.72 eV), C-doped BN nanosheet can also be achieved using BN nanosheet with divacancy as a reactant. (ii) No catalyst is needed, thus no extra step is needed to remove the catalyst. (3) The harmful CO molecule can be used as a reactant and transformed into CO2 or O2 molecule. (4) The selectivity of CO for vacancy defect sites is high. The present results provide an effective theoretical method to synthesize C-doped BN nanosheets, which would be useful for the development of BN nanosheet-based devices.