Recently, two-dimensional materials have received significant attention due to their superior transport and optical properties and their potential roles in future nanoscale devices. Compared to three-dimensional materials, there is still a lack of variety of 2D materials, especially with desired band gap. The number of wide gap 2D materials is quite limited. A good candidate is the well-known h-BN. However, this material has a gap of 5.56 eV, which is too high for a semiconductor, and its fabrication involves boron and nitrogen precursors, which are usually hard to process. In this study, using first principles calculations, we proposed a new 2D material (α-CNH) consisting of C, N, and H. It consists of array of polyethylene chains connected by N atoms in the perpendicular direction. Because of its framework formed by C–C and C–N bonds, α-CNH shows excellent stability and mechanical properties. It is a direct gap semiconductor with a band gap of 3.03 eV, as calculated by the hybrid functional, and exhibits interesting electronic and optical properties that are very anisotropic, as determined via its structure. The mobilities of both electrons and holes in this material are very anisotropic. The mobility along easy direction is 3 to 5 times higher than that along the hard direction. Interestingly, the high mobility directions of electrons and holes are different; this allows to design novel devices in which the high conducting directions can be altered by changing the carriers by applying gate voltage.

The reaction mechanism of Ni(COD)2 catalyzed hydrodesulfurization of aryl sulfide PhSMe with HSiMe3 as the reducing agent has been studied by using density functional theory methods. Both PhSMe-coordinated pathway and “ligandless” pathway have been identified and compared. It is found that these two reaction pathways are kinetically competitive and the σ-complex assisted metathesis (σ-CAM) transition state is the highest point on each energy profile for both pathways. Moreover, both the singlet and triplet reaction pathways of ligand substitutions have been compared and found that both singlet and triplet reaction mechanisms are competitive for the ligand substitution of COD with PhSMe on PhSMe-coordinated pathway while the triplet mechanism holds a distinct advantage over singlet one for that of COD with HSiMe3 on “ligandless” pathway.

Zigzag graphene nanoribbons (ZGNRs) are known to carry interesting properties beyond graphene, such as finite and variable band gaps. More interestingly, the edges of ZGNRs are magnetic due to single occupation of carbon dangling bonds (DB). However, the magnetic moments at two different edge sides couple antiferromagnetically, leading to a zero global moment for ZGNRs. Furthermore, the application of ZGNRs is limited by the high chemical activity of their edges that can be easily oxidized while exposed in air. It has been proposed and intensively studied to protect the edges by passivating them by hydrogenation or adsorption of other molecules such as CO2. In this work, we systematically studied the stability, the structures and the effect of CO2 adsorption at the edges of ZGNRs. Our calculations confirm the experimental observation that the CO2 molecules can be easily absorbed by the ZGNR edges. More interestingly, our calculations show that the asymmetric CO2 adsorption at two edges of ZGNR yields a ferrimagnetic state of ZGNRs that presents a finite global moment. Furthermore, considering the strong bonding between CO2 groups and ZGNRs, we propose that it can be utilized to stitch arrays of ZGNRs together to form new types of 2D materials that inherit the advantageous properties of the nanoribbons, such as finite gaps and novel magnetic properties.

Palladium catalyzed arylthiolation of benzene with 1-(phenylthio) pyrrolidine-2,5-dione to form diaryl sulfide has been studied with the aid of density functional theory (DFT) calculations. Two catalytic cycles (I and II) were considered. In catalytic cycle I, the active species reacts first with benzene, while in catalytic cycle II, the active species reacts first with 1-(phenylthio) pyrrolidine-2,5-dione. The calculations show that catalytic cycle I is more favorable than catalytic cycle II. The reaction proceeds through C–H bond activation, concerted σ-bond metathesis, isomerization, ligand exchange, N–H protonation, and ligand exchange steps, where the concerted σ-bond metathesis is found to be the rate-determining step. The present mechanism slightly differs from the mechanism proposed by experiment, in which an oxidative addition step rather than metathesis is involved. The frontier molecular orbitals were analyzed to understand the nature of the different reaction mechanisms between concerted σ-bond metathesis and oxidative addition. It was found that the HOMO–LUMO interaction results in concerted σ-bond metathesis, while the interaction between HOMO−1 and LUMO gives oxidative addition, and thus, the concerted σ-bond metathesis is more preferred in the arylthiolation reaction.

•H2SO3 as auto-catalyst in the SO2 hydrolysis.•H2SO3 exhibits dramatic catalytic effect compared with H2O.•The nature of the catalytic effect is discussed.•The rate constants from kinetics calculations are performed.The hydrolysis reaction of sulfur dioxide (SO2) to form sulfurous acid involving additional sulfurous acid (H2SO3) was investigated using high-level computational methods. With H2SO3, the reaction takes place via a double proton transfer process with a cage-like structure, which is different from the planar ring structure involved in a corresponding process with an additional water molecule (served as a catalyst). Our results show that H2SO3 is a better catalyst than water, as the barrier height for the H2SO3-catalyzed reaction is only 5.5 kcal/mol, compared to over 25.0 and 15.0 kcal/mol for the reaction without a catalyst and the H2O-catalyzed reaction, respectively. In addition, the sulfurous acid dimer from the H2SO3-catalyzed reaction is more stable than hydrated H2SO3 from the H2O-catalyzed reaction. Considering the existence of sulfurous acid in the aqueous phase and acidic aerosols, as well as the importance of SO2 and H2O in the atmosphere, our results will have potentially significant implications on the homogeneous and heterogeneous nucleation processes.

Two-dimensional (2D) semiconductor materials and the fabrication of related devices have become a new focus of electronics and materials science recently. Compared with three-dimensional (3D) semiconductors, the choice of 2D materials is very limited. Recently, the emerging goal of fabricating functional heterojunctions of 2D semiconductors has spurred a strong need to search for 2D materials that have a large variety of band gaps and band edges. Here, we propose a single layer of B2S3 as a new potential 2D material, conceived directly from its existing layered 3D crystal. Using an advanced hybrid functional method, we demonstrated that 2D B2S3 has a gap of 3.75 eV, filling a missing energy range for 2D materials. Furthermore, by adding extra B atoms at the ‘vacancy’ sites of the B2S3 structure to give a 1:1 stoichiometry, we constructed new 2D BN and graphene allotropes that show large variation in the electronic structure. The BN allotrope exhibits a gap that is 0.99 eV lower than h-BN. Although the structure is significantly different to graphene, the new C allotrope contains a Dirac cone. However, the Dirac point is slightly lower than the Fermi level because of the electron transfer from an adjacent valence band to the Dirac cone states, resulting in a metallic state with both ‘massless’ electrons and massive holes.

The deposition and hydrolysis reaction of SO2 + H2O in small clusters of sulfuric acid and water are studied by theoretical calculations of the molecular clusters SO2–(H2SO4)n–(H2O)m (m = 1,2; n = 1,2). Sulfuric acid exhibits a dramatic catalytic effect on the hydrolysis reaction of SO2 as it lowers the energy barrier by over 20 kcal/mol. The reaction with monohydrated sulfuric acid (SO2 + H2O + H2SO4 – H2O) has the lowest energy barrier of 3.83 kcal/mol, in which the cluster H2SO4–(H2O)2 forms initially at the entrance channel. The energy barriers for the three hydrolysis reactions are in the order SO2 + (H2SO4)–H2O > SO2 + (H2SO4)2–H2O > SO2 + H2SO4–H2O. Furthermore, sulfurous acid is more strongly bonded to the hydrated sulfuric acid (or dimer) clusters than the corresponding reactant (monohydrated SO2). Consequently, sulfuric acid promotes the hydrolysis of SO2 both kinetically and thermodynamically. Kinetics simulations have been performed to study the importance of these reactions in the reduction of atmospheric SO2. The results will give a new insight on how the pre-existing aerosols catalyze the hydrolysis of SO2, leading to the formation and growth of new particles.

Graphenylene, a new form of two-dimensional (2D) carbon allotrope consisting of non-delocalized sp2-carbon atoms, has aroused considerable interest recently due to its thermodynamic stability and porous structure. In this work, density functional theory is used to investigate the hydrogenation and halogenation of graphenylene. The adsorption stability of hydrogen and halogen atoms on graphenylene is discussed at different concentrations of adsorbate atoms. The electronic structures of functionalized graphenylenes show that by controlling the concentration of adsorbate atoms, the band gap of graphenylene could be tuned over a wide range, from 0.075 to 4.98 eV by hydrogenation and 0.024 eV to 4.87 eV by halogenation.

The mechanisms of NO reduction by H2 on the Pt(100) surface and the surface modified with subsurface oxygen atoms (Md-Pt(100)) are studied by first-principles calculations. Similar catalytic activity toward NO dissociation is found on both surfaces with barriers of 0.86 and 0.96 eV, respectively. The pathway of N + N → N2 rather than NO + N → N2 + O is the N2 formation pathway on the Pt(100) surface, while these two pathways are competitive on the Md-Pt(100) surface. The NH3 formation is almost negligible, and reductant hydrogen can effectively remove the surface oxygen on both surfaces. The microkinetic analysis further confirms that, compared to the high selectivity toward N2O (almost 100% at 300–500 K) on the clean surface, higher N2 low-temperature selectivity (larger than 90%) is achieved on the Md-Pt(100) surface under lower pressure. The present study shows that subsurface oxygen has an enhanced effect for improving the N2 selectivity of NO reduction on Pt catalysts.

The detailed reaction mechanism for the isomerization of 1,3-conjugated dienes catalyzed by the ruthenium hydride complex RuHCl(CO)(H2IMes)(PCy3) has been studied with the aid of density functional theory (DFT) calculations. Both cis and trans isomers of a 1,3-conjugated diene were considered as the reactants. For each isomer, two catalytic cycles were calculated, which (respectively) generate a 1,3-hydride shift product or a 1,5-hydride shift product. Both catalytic cycles proceed via alkene migratory insertion into the Ru–H bond, σ-allyl ruthenium isomerization, and β-H elimination steps. Our computational study shows that the cis isomer of the model reactant reacts preferentially via the pathway leading to the 1,5-hydride shift product, consistent with the experimental results. The σ-allyl ruthenium isomerization step is found to be crucial for reaction regioselectivity. Strong binding of the C═C bond to Ru is involved in the generation of the 1,5-hydride shift product. In addition, the steric effect of the bulky N-heterocyclic carbene ligand in ruthenium hydride RuHCl(CO)(H2IMes)(PCy3) was considered theoretically.

Effects of ammonia and water molecules on the hydrolysis of sulfur dioxide are investigated by theoretical calculations of two series of the molecular clusters SO2-(H2O)n (n = 1–5) and SO2-(H2O)n-NH3 (n = 1–3). The reaction in pure water clusters is thermodynamically unfavorable. The additional water in the clusters reduces the energy barrier for the reaction, and the effect of each water decreases with the increasing number of water molecules in the clusters. There is a considerable energy barrier for reaction in SO2-(H2O)5, 5.69 kcal/mol. With ammonia included in the cluster, SO2-(H2O)n-NH3, the energy barrier is dramatically reduced, to 1.89 kcal/mol with n = 3, and the corresponding product of hydrated ammonium bisulfate NH4HSO3-(H2O)2 is also stabilized thermodynamically. The present study shows that ammonia has larger kinetic and thermodynamic effects than water in promoting the hydrolysis reaction of SO2 in small clusters favorable in the atmosphere.

The detailed reaction mechanism for the Cu(I)-catalyzed cross-coupling of (diazomethyl)benzene with trimethylsilylethyne and tert-butylethyne was studied with the aid of density functional theory calculations. For both reactions, two catalytic cycles were considered. In one catalytic cycle, the active species reacts first with trimethylsilylethyne or tert-butylethyne, whereas, in the other one, the active species reacts first with (diazomethyl)benzene. In both catalytic cycles, the copper acetylide formation, copper carbene migratory insertion, and protonation steps are involved. The calculation results show that the protonation step is crucial for the product selectivity. In addition, the reaction of diazoethane with tert-butylethyne and the reaction of (diazomethyl)benzene with phenylacetylene were also considered theoretically.

The possible C2Hy (y = 2–6) formation reactions (CHx + CHz → C2Hy (y = x + z)) and activated second-order CHx+1 + CHz–1 reactions (CHx + CHz → CHx+1 + CHz–1) during CH4 dissociation on Cu(100) surface have been investigated by using the density functional theory. Our results show that C2Hy (y = 2, 4) formation reactions are favorable both kinetically and thermodynamically, compared with the direct dehydrogenation of CH4 (CHx → CHx–1 + H) and second-order CHx+1 + CHz–1 reactions. The second-order CHx+1 + CHz–1 reactions are less competitive compared with the direct dehydrogenation of CHx. Both DFT calculations and microkinetic model demonstrate that the reaction CH + CH → C2H2 is a major channel to produce C2Hy at a temperature of 860 °C, followed by CH3 + CH → C2H4. When the H2 influence is introduced, the major intermediate changes from CH to CH3 on Cu(100) surface with the increase of H2 partial pressure, while the coverage difference between CH and CH3 is not significant. This means that both species will have a large influence on the graphene growth mechanism.

The hydrogen abstraction reaction of CF3CH2CH2OH + OH has been studied theoretically by dual-level direct dynamics method. The required potential energy surface information for the kinetic calculation was obtained at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level. Five stable conformers of CF3CH2CH2OH have been located. For each conformer, there are three potential H-abstraction sites (Cα, Cβ and –OH), and some of the H atoms can be abstracted by more than one abstraction channel due to the different attack orientations of the incoming OH radical. As a result, 31 distinct Habstraction channels have been identified for the reaction. The individual rate constants for each Habstraction channel were calculated by the improved canonical transition-state theory with smallcurvature tunneling correction (ICVT/SCT), and the overall rate constant was evaluated by the Boltzmann distribution function. It is shown that the calculated rate constant is in good agreement with the available experimental data at 298 K, and exhibits negative temperature dependence with 200–350 K. H-abstraction from the α site dominates the reaction at low temperatures, while the contributions from the β and OH abstractions should be taken into account as temperature increases. The fitted four-parameter expressions within 200–1000 K for the overall rate constants as well as the rate constants from the α, β and OH abstractions were given to provide good estimation for future laboratory investigations. In addition, because of the lack of available experimental data for the product radicals involved in the reactions, their enthalpies of the formation (ΔHf,298°) were predicted via isodesmic reaction at the MCG3-MPWB//M06-2X/aug-cc-pVDZ level.Graphical abstractHighlights► The PES for the reaction of CF3CH2CH2OH + OH was explored. ► Five conformers of CF3CH2CH2OH were considered in the kinetic calculation. ► The individual ICVT/SCT rate constants for each H-abstraction channel were evaluated. ► The selectivity of reaction sites was determined.

The enzyme α-galactosidase (α-GAL), a member of glycoside hydrolase family 27, catalyzes the removal of a nonreducing terminal α-galactose residue from polysaccharides, glycolipids, and glycopeptides. α-GAL is believed to have the double displacement retaining reaction mechanism. In this work, the glycosylation step catalyzed by human α-GAL was computationally simulated with quantum mechanics/molecular mechanics metadynamics. Our simulations show that the overall catalytic mechanism follows a DN*AN-like mechanism, and the transition state has a oxocarbenium ion like character with a partially formed double bond between the ring oxygen and C5′ carbon atoms. In addition, the galactosyl ring of the substrate follows a conformational itinerary of 4C1 → [E3/4H3]⧧ → 1S3 along the reaction coordinate.

The adsorption, decomposition, and oxidation of methanol on Ir(111) were studied based on periodic density functional calculations. Each elementary step in the methanol decomposition reaction on clean Ir(111) via O–H, C–H, and C–O bond scissions was considered. The formation mechanisms of CO, CO2, H2O, and CHx(x = 1–3) were elucidated. The results show that the desorption and decomposition of methanol are competitive on a clean surface, and the presence of O or OH has a larger effect on some specific reaction steps. The surface-assisted decomposition of methanol mainly follows two competitive dehydrogenation pathways initialed with O–H and C–H bond scissions, respectively, i.e., CH3OH → CH3O → HCHO → CHO → CO and CH3OH → CH2OH → CHOH → CHO → CO. The predosed O enhances the dehydrogenation of CH3OH into CH3O, while the surface is slightly more active toward the C–H bond breaking of CH3O than O and OH. HCHO would like to dehydrogenate into CHO assisted by the surface or OH, followed by OH-assisted dehydrogenation into CO. CO combines with O to yield CO2. However, if the surface O coverage is higher, CO2 could be formed via the oxidation pathway of HCHO, i.e., HCHO H2CO2 HCO2 → CO2. The comparison between theoretical results and experimental observation was made.

The decomposition of formaldehyde (HCHO) and possible pathways for the formation of C2H4 and CH4 on clean and oxygen-predosed V(100) surfaces were studied by periodic density functional theory (DFT). It is shown that both C–H and C–O bond scissions of HCHO are thermodynamically and kinetically favorable on clean V(100). Three reaction pathways for the formation of C2H4 and two for the formation of CH4 were determined. Our results suggest that the preferred pathway for C2H4 formation at low temperature is the coupling of two methylenes (CH2) produced by an early C═O dissociation step at lower O coverage; while as the increase of the on-surface O coverage, this path is suppressed whereas the direct coupling of HCHO to form intermediate OCH2CH2O is favored at high temperature. For the formation of CH4, different mechanisms are also identified corresponding to the two reaction regions. The low-temperature reaction likely occurs via successive hydrogenation of CH2, while the high-temperature reaction may proceed via the CH3O intermediate formed by hydrogenation of HCHO first. The present calculations show that the oxygen deposited on the V(100) surface contributes to the shifting of the mechanisms in low- and high-temperature regions, in line with the experimental results [Shen, M.; Zaera, F. J. Am. Chem. Soc. 2009, 131, 8708].

Aliphatic aldoxime dehydratase (Oxd) catalyzes the dehydration of aliphatic aldoximes (R–CH═N–OH) to the corresponding nitriles (R–C≡N). Quantum mechanics/molecular mechanics (QM/MM) calculations are performed to elucidate the catalytic mechanism of the enzyme on the basis of the X-ray crystal structure of the Michaelis complex. On the basis of the calculations, we propose a complete catalytic cycle of Oxd in which the distal histidine (His320) acts as a general acid/base. In the Michaelis complex, the elimination of the hydroxyl group of aldoxime is facilitated by His320 donating a proton to the hydroxyl group in a concerted way, which is the rate-limiting step. The formed intermediate has a ferric heme iron and an unpaired electron on the nitrogen atom of the substrate coupled to a singlet state. The second step is the deprotonation of the β-hydrogen of the substrate by His320 after the substrate rotates about the Fe–N bond for ∼180° to yield the neutral product. In the meantime, the heme iron goes back to ferrous state by a one-electron transfer from the substrate to the ferric heme iron, and His320 goes back to the protonated state to proceed with the following reaction. The functions of the protein environment and the active site residues are also discussed.

The decomposition of CH3OH on clean and oxygen-predosed V(100) surfaces was studied on the basis of periodic density functional calculations and microkinetic modeling. The results indicate that the O–H bond scission of CH3OH is thermodynamically and kinetically favorable on clean V(100) while the C–H and C–O bond scissions are unlikely to occur at low temperature, and as a result, CH3O is the major intermediate in the decomposition process. The C–O bond scission of CH3O to form CH3 is much easier than the C–H bond scission to form HCHO. Hydrogenation of CH3 by the surface hydrogen from dissociating CH3OH and CH3O is responsible for the desorption of CH4 at low and high temperatures, respectively. HCHO further undergoes decomposition or/and coupling to form CO or/and C2H4. When oxygen is preadsorbed on the surface at low coverage, the O–H bond scission of CH3OH is virtually not affected, while the cleavages of the C–O and C–H bonds from CH3O are inhibited in different degrees, leading to the decrease in the ratio of CH4 produced at the low temperature relative to that at the high temperature. All products are delayed in temperature. The results are in good agreement with experimental observations.

Density functional theory (DFT) calculations combined with microkinetic analysis were performed to study the behavior of ammonia on clean, oxygen- and hydroxyl-predosed Ir(100). It is shown that the predosed oxygen or hydroxyl promotes NH3 and NH dehydrogenation steps, while NH2 dehydrogenation is slightly inhibited relative to clean Ir(100). In both cases, the hydrogen transfer from NHx species to predosed O or OH is favored over thermal decomposition of NHx. Furthermore, the predosed O exhibits higher activity on NH3 and NH dehydrogenation steps than OH, while the case is reversed for NH2. On clean Ir(100), N + N pathway is the major N2 formation pathway when TPD experiment starts from 200 K, and N + NH is also involved but less competitive; however, three pathways N + N, N + NH, and NH + NH are all possible with respect to TPD experiment starting from 410 K. On O- and OH-predosed Ir(100), N + N pathway is the predominant pathway and is enhanced by the predosed O or OH. The microkinetic analysis further confirms that N2 is the resulting product at different temperatures and ratios of NH3/O2, and the formation of NO is unfavorable.

Quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations were performed to investigate the methylation of 6-mercaptopurine catalyzed by thiopurine S-methyltransferase. Several setups with different tautomeric forms and orientations of the substrate were considered. It is found that, with the orientation in chain A of the X-ray structure, the substrate can form an ideal near-attack configuration for the methylation reaction, which may take place after the deprotonation of the substrate by the conserved residue Asp23 through a water chain. The potential of mean force (PMF) of the methyl-transfer step for the most favorable pathway is 19.6 kcal/mol, which is in good agreement with the available experimental rate constant data.

Density functional theory (DFT) calculations using the hybrid functional B3LYP have been performed to investigate the catalytic mechanism of hydroxynitrile lyase from Hevea brasiliensis (Hb-HNL). This enzyme catalyzes the cleavage of acetone cyanohydrin to hydrocyanic acid plus acetone. Two models (A and B) of the active site consisting of 105 and 155 atoms, respectively, were constructed on the basis of the crystal structure. Good consistency between the two models provides a verification of the proposed mechanism. Our calculations show that the catalytic reaction proceeds via three elementary steps: (1) deprotonation of the OH-Ser80 by His235 and concomitant abstraction of a proton from the substrate hydroxyl by Ser80; (2) the C−C bond cleavage of the acetone cyanohydrin; and (3) protonation of the cleaved cyanide by His235. The cleavage of the C−C bond is the rate-limiting step with the overall free energy barrier of 13.5 kcal/mol for relatively smaller model A (14.9 kcal/mol for a larger model B) in the protein environment, which is in good agreement with experimental rate. The present results give support to the previously proposed general acid/base catalytic mechanism, in which the catalytic triad acts as a general acid/base. Moreover, the calculated results for model C, with the positive charge of Lys236 removed from model A, show that Lys236 with the positive charge plays a vital role in lowering the reaction barrier of the rate-determining and helps in stabilizing the negatively charged CN− by forming a hydrogen bond with the substrate, consistent with the experimental analysis.

The mechanism and kinetics of the reaction CF3CH2OCHO + Cl are investigated theoretically by using a dual-level direct dynamics method. The geometries and frequencies are calculated at the B3LYP/6-311G(d,p), B3LYP/6-311+G(d,p), and MP2/6-31G(d,p) levels, and high-level single-point energy calculations are performed at the BMC-CCSD level. It is shown that the reaction proceeds exclusively via two hydrogen abstraction channels, while the Cl addition–elimination channel is unfavorable. Furthermore, the rate constants of the two H-abstraction channels are evaluated by means of canonical variational transition-state theory (CVT) with the small-curvature tunneling (SCT) correction over a temperature range of 200–1000 K. The overall rate constant at room temperature is in good agreement with the experimental value. This study show that the formyl-H-abstraction channel is the major reaction pathway at low temperatures, while as the temperature increases, methylene-H-abstraction channel becomes more important and competes with the former. The three parameter rate-temperature expression is fitted to be k = 0.17 × 10−20 T3.13exp(−23.9/T) cm3 molecule−1 s−1 (200–1000 K). The present study may assist in further laboratory work.

A dual-level direct dynamics method is employed to perform the dynamics calculations for the multi-channel reactions CH3CH2Br + O(3P) → products (R1) and CH3CH2Br + Cl → products (R2). Four reaction channels, i.e., one α-hydrogen, two β-hydrogen, and one bromine-abstractions, are identified for each reaction. The geometries and frequencies of all the stationary points are optimized at the BH&H-LYP/6-311G(d, p) level. The complexes with energies less than those of the reactants or products are found at entrance or exit of each reaction channel, which indicate that the reactions may proceed via an indirect mechanism. The energy profiles are further refined at the G3//BH&H-LYP level. Then, the rate constants are calculated by canonical variational transition-state (CVT) theory incorporating the small-curvature tunneling method (SCT) correction in the temperature range of 220–2000 K. The theoretical rate constants are in good agreement with the experimental ones. Theoretical calculations show that the Br-abstraction channel should be negligible due to its much higher barrier height than the others. As to the three hydrogen-abstraction channels, α-hydrogen abstraction is the major pathway and the contribution of β-hydrogen abstraction become important with the temperature increasing.

The hydrogen abstraction reactions of CF3CF2CFH2 and CF3CFHCF2H with OH radicals and Cl atoms have been studied theoretically by a dual-level direct dynamics method. Two stable conformers of CF3CF2CFH2 with Cs and C1 symmetries and all possible abstraction channels for each reaction are all taken into consideration. Optimized geometries and frequencies of all the stationary points and extra points along minimum-energy path (MEP) have been computed at the BB1K/6-31+G(d, p) level of theory. To refine the energy profile of each reaction channel, single point energy calculations have been performed by the BMC-CCSD method. The rate constants are evaluated by canonical variational transition state theory (CVT) with the small-curvature tunneling correction method (SCT) over a wide temperature range of 200–1,000 K. The detailed branching ratios of four reactions are discussed. The good agreement found between our theoretical rate constants and the available experimental data suggests that the present approach could provide a reliable prediction for the CF3CFHCF2H + Cl reaction about which there is little experimental information. The kinetic calculations show that the SCT effect plays an important role in all channels. In addition, in order to further reveal the thermodynamic properties, the enthalpies of formation of the reactants (CF3CF2CFH2 and CF3CFHCF2H) and the product radicals (CF3CF2CFH, CF3CFCF2H, and CF3CFHCF2) are evaluated by applying isodesmic reactions at both BMC-CCSD//BB1K/6-31+G(d, p) and MC-QCISD//BB1K/6-31+G(d, p) levels of theory.

The hydrogen abstraction reactions of the CF3CH2CF3 with the OH radicals (R1), F (R2), and Cl (R3) atoms have been studied theoretically over a wide temperature range 200–1000 K. In this study, the recently developed hybrid density functional theory BB1K is used to obtain reaction path information including the geometries and frequencies of the stationary points. To refine the energies, single-point energy calculations were performed at the BMC-CCSD level using the BB1K geometries. The rate constants are carried out by the canonical variational transition state theory (CVT) with the small-curvature tunneling correction method (SCT). It is found that the activation energies for the title reactions are on the order of R3 > R1 > R2 and the rate constants exhibit just the opposite order, i.e., k2 > k1 > k3. The calculated CVT/SCT rate constants are compared with the available experimental values in the temperature region 269–413 K. The temperature dependence of the rate constants can be expressed by three-parameter Arrhenius expressions (cm3 mol−1 s−1): k1 = 1.18 × 10−19T2.51 exp(−1761.16/T), k2 = 2.47 × 10−15T1.36 exp(−689.34/T), and k3 = 4.24 × 10−21T3.22 exp(−2819.55/T) cm3 mol−1 s−1, respectively. Furthermore, in order to further reveal the thermodynamics properties, the enthalpies of formation of CF3CH2CF3 and CF3CHCF3 are studied using isodesmic reactions.

Two-dimensional (2D) semiconductor materials and the fabrication of related devices have become a new focus of electronics and materials science recently. Compared with three-dimensional (3D) semiconductors, the choice of 2D materials is very limited. Recently, the emerging goal of fabricating functional heterojunctions of 2D semiconductors has spurred a strong need to search for 2D materials that have a large variety of band gaps and band edges. Here, we propose a single layer of B2S3 as a new potential 2D material, conceived directly from its existing layered 3D crystal. Using an advanced hybrid functional method, we demonstrated that 2D B2S3 has a gap of 3.75 eV, filling a missing energy range for 2D materials. Furthermore, by adding extra B atoms at the ‘vacancy’ sites of the B2S3 structure to give a 1:1 stoichiometry, we constructed new 2D BN and graphene allotropes that show large variation in the electronic structure. The BN allotrope exhibits a gap that is 0.99 eV lower than h-BN. Although the structure is significantly different to graphene, the new C allotrope contains a Dirac cone. However, the Dirac point is slightly lower than the Fermi level because of the electron transfer from an adjacent valence band to the Dirac cone states, resulting in a metallic state with both ‘massless’ electrons and massive holes.