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Defect-engineering of few-layer graphene, by modulating local electronic structure and forming highly-active reaction sites, benefits the charge storage and electrochemical reactions. To control defect morphology of graphene, herein, we devise a CH4- chemical vapor deposition (CVD) approach to directly synthesize graphene film with extremely high defect density of 5.9 × 1011 cm−2 and relatively high crystallinity at a low temperature of 700 °C. The C atoms involved in Cu bulk are induced to segregate onto the Cu surface to establish synergetic C–Cu complex catalyst. Theoretical evidence verifies that the interaction between the Cu and C atoms in form of C cluster atop the Cu plane lowers energy barriers for stepwise decomposition of CH4. The 13CH4 isotope data demonstrate that the C clusters are integrated sequentially into the graphene lattice, unraveling the dual roles of carbon impurities. The defective graphene film exhibits a specific capacitance of 10.6 μF/cm2 and excellent electro-catalytic performance. Such a self-induced synergetic catalyst can innovate the methodology of catalysis engineering for controllable synthesis of graphene and other 2D materials.

This work presents a theoretical investigation on the electronic properties of double atomic carbon chains bridging graphene electrodes with density functional theory in combination with non-equilibrium Green's function. The influence of strain on the conductance of atomic carbon chains is significant. However, the coupling effect between adjacent chains dominates the intrinsic transport of double atomic carbon chains. For the coupled double atomic chains, the electron conductance of even-numbered atomic chains is significantly enhanced, while the electron conductance of odd-numbered atomic chains decreases to a certain degree, and the dependence of the conductance of double atomic chains on electrode configuration is stronger than the corresponding single atomic chain. More intriguingly, the coupled double atomic chains exhibit excellent spin-filtering properties with antiparallel spins on two electrodes. The current spin polarization stems from the coupling-induced changes of electron density and band offset reaches 100%. The coupled double atomic carbon chains have great potential application in spintronic devices and carbon-based field-effect transistors.

In this work, a systematical investigation on the transformation of tetrachloro-p-benzoquinone (TCBQ) under UV irradiation (at 253.7 nm) in aqueous solution has been conducted through quantum chemical calculations. The UV irradiation at 253.7 nm could induce the excitation of TCBQ to its first excited singlet state, followed by the intersystem crossing to its first triplet state. In aqueous solution, the first triplet state of TCBQ was thermodynamically and kinetically feasible to react with H2O via 1,4-addition, where the addition of OH− to the α–β conjugated system was the dominant step. Interestingly, with the addition of hydroxyl to TCBQ, the dechlorination of TCBQ occurred with the formation of the monohydroxylated product of TCBQ (OH-TriCBQ). The UV photolysis pathway of OH-TriCBQ was similar to that of TCBQ, and the 1,4-addition of OH− to the ortho-position of the hydroxyl was the most efficient pathway. The dechlorination by 1,4-addition of OH− was also observed for OH-TriCBQ. With much larger forward energy barriers, the nucleophilic addition of carbonyl by OH− (i.e., 1,2-addition) might be less important for the UV photolysis of TCBQ and OH-TriCBQ. The findings in the present study may help to understand the transformation of TCBQ in aqueous solution.

The hydrogen adsorption capacity of dual-Ti-doped (7, 7) single-walled carbon nanotube (Ti-SWCNTs) has been studied by the first principles calculations. Ti atoms show different characters at different locations due to local doping environment and patterns. The dual-Ti-doped SWCNTs can stably adsorb up to six H2 molecules through Kubas interaction at the Ti2 active center. The intrinsic curvature and the different doping pattern of Ti-SWCNTs induce charge discrepancy between these two Ti atoms, and result in different hydrogen adsorption capacity. Particularly, eight H2 molecules can be adsorbed on both sides of the dual-Ti decorated SWCNT with ideal adsorption energy of 0.198 eV/H2, and the physisorption H2 on the inside Ti atom has desirable adsorption energy of 0.107 eV/H2, ideal for efficient reversible storage of hydrogen. The synergistic effect of Ti atoms with different doping patterns enhances the hydrogen adsorption capacity 4.5H2s/Ti of the Ti-doped SWCNT (VIII), and this awaits experimental trial.

Recent successful syntheses of azulene-defect graphene nanosheets (GNSs) pave a path for the applications of those GNSs in nonlinear optics , since azulene-defect GNSs maintains the thermal stability of carbon-based nanomaterials and possesses potential large nonlinear optical (NLO) responses. In the present work, azulene-defect GNSs with different relative position and orientation are designed for applications in optoelectronics and nonlinear optics. The all-carbon azulene-defect GNS Paral-2 with parallel orientated azulenes has good electronic kinetic stability as well as a large static first hyperpolarizability ( 0>) of 1032.28 × 10−30 esu (18.43 × 10−30 esu per heavy atom). The Paral-0-4N, formed by replacing four edge C atoms with N atoms in the GNS Paral-0, has the largest (1247.68 × 10−30 esu, 22.28 × 10−30 esu per heavy atom) due to the charge transfer based electron excitations and the polar structure while with enhanced electronic kinetic stability. The two-dimensional second order NLO spectra of those azulene-defect GNSs provide vital information for further experimental exploration and applications. The introduction of polar azulene in GNSs to improve the NLO responses and doping of nitrogen atoms to enhance the electronic kinetic stability of GNSs provide a practical strategy and useful information for future NLO materials design.

Metallo-β-lactamase (MβL) is a eubacterial zinc metallo-hydrolase superfamily. Despite their well-known lactamase activities, MβL family members also have the ability to catalyze phosphotriester hydrolysis with different phosphotriesterase activities. In the present study, based on crystal structure comparisons of the related MβL members, a series of models was constructed and calculated using the density functional theory (DFT) method to explore the relationship between active-site changes and phosphotriesterase activities. These calculations show that the energetic barriers for phosphotriesterase activity are considerably reduced due to active-site differences, which describes an evolutionary trend for the development of phosphotriesterase activity in the MβL superfamily. The key event is the appearance of a specialized and negatively charged residue bridging both zinc ions, which plays the two important roles of maintaining charge balance and stabilizing the binuclear active-site structure. This pathway is also consistent with the evolutionary relationships determined by phylogenetic tree analysis using complete residue sequences. Our studies provide the first methodology to explore the development of a new enzyme activity within a superfamily, and to shed new light on understanding the catalytic mechanism from an evolutionary perspective.

In this work, the effect of alcohols as hydrogen donors on hydrated electron (e aq − ) generation from p -benzoquinone ( p -BQ) photolysis was investigated by quantum chemical calculations and experiments to further understand the underlying mechanisms associated within the p -BQ/UV process. Theoretically, the UV photolysis of p -BQ at 253.7 nm in the presence of H 2 O could induce the formation of p -HOC 6 H 4 OH and hydroxy- p -benzoquinone, which was almost independent of the addition of CH 3 OH. While, the first triplet state of hydroxy- p -benzoquinone preferred to react with CH 3 OH (rather than H 2 O) to release the corresponding semiquinone radical and hydroxymethyl radical ( CH 2 OH). These two radicals could induce the reduction of p -BQ to p -benzosemiquinone radical and thus enhanced the formation of p -HOC 6 H 4 OH as the precursor of e aq − . Experimentally, the detection of e aq − generated in the process was accomplished by the degradation of monochloroacetic acid (MCAA) (the probe of e aq − ). With the addition of CH 3 OH, the degradation of MCAA was accelerated in the p -BQ/UV process. A similar acceleration was also observed by the addition of ethanol or 2-propanol with the α-H. However, tert -butanol, which is without the α-H in the structure, didn’t induce the acceleration. Since the quinone-like and alcoholic groups are widely distributed in the environment, these findings may improve the understanding of the photochemistry of quinones in the presence of alcohols with the α-H.

Phase-change memory (PCM) material is the promising material system for nonvolatile-memory technology. Performance optimization of PCM device urgently requires the deeper clarification of its material “Gene”. In this study, through first-principles calculations, p-orbital-aligned atom chains are identified to play important roles in governing optoelectronic reflectivity in amorphous Ge2Sb2Te5. These atom chains make the electronic state of the amorphous Ge2Sb2Te5 hold strong electron-polarized components, thereby governing the optical property. The present study offers a new understanding of “Gene” for PCM materials which benefit the material design and the performance improvement of PCM devices.

Two-dimensional (2D) semiconductors have attracted considerable attentions from electronic-engineering community due to their unique electronic properties. Especially, the inherent advantage of scaling semiconductor into atomic thickness has raised the prospect of possible extension of the Moore’s law. To achieve 2D electronics, a full comprehension of semiconductor defect physics and chemistry is indispensable due to its controlling electrical performance of 2D materials and functionalizing their devices. In this review, first we explain why 2D semiconductors is important for nanoelectronics and optoelectronics. Second, we elucidate how native defects or intentional impurities affect and control electrical characteristic in 2D semiconductors, such as carrier concentration and their conductive type. In this section, experimental pictures of defects and several updated theoretical methods to evaluate carrier ionization energies of defects and their conductive type are introduced in detail. Third, typical device experiments are shown to demonstrate a direct role of defects to functionalize 2D electronic device. Furthermore, a database of popular defects and their electrical properties in current popular 2D semiconductors is summarized for references. Last, we discuss the challenges and potential prospects of defect engineering for 2D devices. The present paper offers important viewpoints from semiconductor defects to design the emerging 2D electronics.

A p -benzoquinone ( p -BQ)/UV process to induce hydrated electron (e aq − ) generation was predicted by quantum chemical calculations and validated by experiment in this work. Theoretically, the photolysis of p -BQ under UV irradiation at 253.7 nm could induce water to generate e aq − with a molar ratio of 1:2 via the direct triplet mechanism, in which 1,4-addition reaction of the first triplet state of p -BQ with water was the key step. Experimentally, monochloroacetic acid (MCAA) (the probe of e aq − ) was used to detect e aq − generated in the p -BQ/UV process. The generation efficiency showed a positive linear dependence on the p -BQ concentration, which illustrated the crucial role of p -BQ on the generation of e aq − . During the photolysis, p -hydroquinone was the primary intermediate for the generation of e aq − . Kinetically, the energy barriers of the e aq − generation from p -HOC 6 H 4 OH, p -HOC 6 H 4 O − and p - − OC 6 H 4 O − were 100.8 kcal mol −1 , 46.5 kcal mol −1 and 5.6 kcal mol −1 , respectively. Both the experimental and theoretical results show that the generation of e aq − was much more efficient from the anions than that from p -HOC 6 H 4 OH. The findings in the present study may help to understand the mechanism of e aq − generation from natural organic matters (NOM), since quinone-like groups are usually contained in NOM.

A new carbon-based morphology, graphene spirals (GSs), possesses interesting electronic features with inter-layer interaction and intra-layer interaction, ascribed to its unique intra-system electronic coupling states. The spin-polarization and the tunneling patterns of GSs manipulated by the periphery structural modification were investigated in detail with first principle calculations. The spin-polarized edge-states and transport properties can be enhanced and modulated by the constructed trigonal corners efficiently. Governed by the position and the number of the introduced carbon-hexagons, diverse spin-polarized tunneling states and various edge-state couplings between central spiral structure and electrodes can be achieved. More significantly, the contribution of inter-layer tunneling and intra-layer tunneling can be dominated by the topological signatures of GSs. For all spiral conformations, inter-layer tunneling always contributes to the net spin-dependent current. Remarkably, when carbon-hexagons are introduced at some typical positions, the complete spiral current along spiral construction is induced by intra-layer tunneling. Those features provide a good tunability of spin-polarized couplings and tunneling patterns in GSs for spintronic applications.

A phenol/UV (253.7 nm) process to generate hydrated electron (eaq−) was experimentally and theoretically studied in the present work, where monochloroacetic acid (MCAA) was selected as the probe of eaq−. It was demonstrated that the eaq− generation efficiency was dependent on the phenol concentration and pH. To interpret the dependence, a mechanism for the generation of eaq− from phenol was proposed and confirmed by the quantum chemical calculations. Theoretically, phenol could eject eaq− and phenoxyl radical (C6H5O ), followed by the addition of hydroxyl ion (OH−) to C6H5O , and the simultaneous formation of phenol and p-hydroquinone was accomplished by hydrogen abstraction of the adduct with C6H5O as hydrogen acceptor (period I). The generated p-hydroquinone could also release eaq− with p-benzoquinone as the product (period II). Totally, one mole of phenol could generate four moles of eaq− via two periods, and two moles were generated in period I and two moles were in period II. Experimentally, eaq− could be ejected from phenol and phenolate, and the molar ratios of the species were determined by pH. Kinetically, the energy barriers of the electron release from phenol and phenolate were 63.7 kcal mol−1 and 62.3 kcal mol−1, respectively, which confirmed that the generation of eaq− from phenolate was much more efficient than that from phenol. These results may promote the development of novel eaq− reduction processes based on the phenolic compounds, since they are abundant in the environment.

Because of the remarkable semi-metallicity and edge states, graphene-based nanoelectronics has become an intense arena in low-dimensional atomic device science and technology. Nowadays, various single atomic chains have been successfully fabricated, which can serve as multi-functional interconnects to bridge atomic devices. Using first principles approach, the spintronic applications of graphene-based carbon atomic chains and boron nitride atomic chains MTJs (magnetic tunnelling junctions) are systematically investigated in this work. The results show that the half-metallicity is only contact-dominated (sp and sp2 contacts), which cannot be switched by gate voltages, strain, the length of atomic chains, or the width of zigzag graphene nanoribbon leads. The intrinsic physics is that the electronic coupling in sp junctions provides partial transmission states for both spin currents, while one spin state is completely blocked by the electronic coupling in sp2 junctions. Therefore, the sp2 junctions present half-metallicity and remarkable tunnelling magneto-resistance (105%–106%), demonstrating the potential applications as spin-valve.

The development of carbon-based catalysts with excellent activity for hydrogen evolution reaction (HER) is highly desirable but still remains a significant challenge. Chemical doping and morphology engineering are paramount to enhance their catalytic performance toward HER. Herein, we present a novel and effective strategy to synthesize heteroatoms-doped three-dimensional (3D) carbon nanotubes/graphene hierarchical architecture (N,S-CNTs/N,S-G) on layered double oxide substrates, in which the N,S-doped CNTs are in-situ grown on both sides of N,S-doped graphene, by two differentiated chemical vapor deposition (CVD) processes. The high concentrations of N and S dopants (up to 6.5 at.%) provide sufficient catalytic active sites for HER, while the CNTs seamlessly grafted on graphene ensure the excellent electric conductivity of N,S-CNTs/N,S-G hybrids. Consequently, the 3D N,S-CNTs/N,S-G composites display superior electrocatalytic activity for HER with an onset potential of 62 mV vs. RHE (achieve current density of 1 mA cm−2) and a small overpotential of 126 mV at 10 mA cm−2, which outperforms most of reported chemical doped carbon-based composites. The synthetic strategy facilitates the fabrication of other heteroatoms-doped 3D electrochemical catalysts.

Electronic spectra, and the nonlinear optical (NLO) properties of five isomers of C96 were investigated using density functional theory and semi-empirical methods. The simulated electronic spectra of C2:181, C1:144, C1:145, and C2:176 have strong absorptions above 500 nm. The electronic spectra of C1:144, C1:145, and C2:176 are similar. The third-order NLO properties of the isomers were analyzed under an external field. Small structural differences between C1:144 and C1:145 result in NLO responses that occur at different external fields. Entropy effects on the NLO properties are significant. The NLO responses of the five most stable isomers differ in the concentration averaged sample.

Density functional theory based calculations have been employed to investigate structures and properties of coupled tetragonal pyramid (CTP) Pt 7 based Pt (7 − x ) Ni x ( x = 1, 2, 3) bimetallic clusters, and the reaction mechanism of methanol dehydrogenation to CO on Pt 7 and PtNi bimetallic clusters. The models chosen to catalyze the methanol are Pt 7 (CTP, quintet) cluster and Pt 5 Ni 2 (I) cluster (two Pt atoms in the bottom of Pt 7 (CTP) are replaced by Ni atoms) which is the most stable structure among all the isomers of Pt (7 − x ) Ni x ( x = 1, 2, 3). The methanol dehydrogenation on Pt 7 (CTP) cluster preferentially proceeds along the pathway of CH 3 OH → CH 2 OH → CH 2 O → CHO → CO, while on Pt 5 Ni 2 (І) the pathway of CH 3 OH → CH 3 O → CH 2 O → CHO → CO is more favorable. In addition, the complete dehydrogenation product of methanol, CO, can more easily dissociate from Pt 5 Ni 2 (I) than that on Pt 7 . Electronic configuration analysis shows that charge transfer from Ni to Pt and results in increase of the electron density in Pt 5d orbitals. Moreover, the density of states (DOS) at Fermi level of clusters reduces gradually as the increase of the doped Ni atoms and this improves the catalytic activity for methanol decomposition.

A series of alkali metal doped carbon bowls have been designed to optimize the nonlinear optical (NLO) contrast and achieve rapid transformation between ON and OFF states in NLO switch. Transformation among metal doped conformations can be achieved by migration of alkali metal on the bowl surface and bowl-to-bowl inversion. The type of doping agent and doping site on the curved carbon surface significantly influences the amplitude of the first hyperpolarizability of those metal doped systems. Large difference in charge transfer and interaction between the metal and buckybowl is responsible for the large hyperpolarizability contrast among alkali metal doped isomers.

First-principles calculation identifies elementary processes in the thermal reduction of graphene oxide (GO) and reveals the effects of alkaline-earth metals (AEMs) in recovering the graphene. These metals are highly effective in removing residual oxygen groups resistive to thermal reduction, as well as healing the defects formed during the reduction, such as the carbonyl groups. In the AEM-assisted reduction, the AEMs serve as an electron reservoir of high chemical potential that forces electron transfer to the GO, whereas pristine carbon regions on the GO serve as a “bridge” to facilitate the electron transfer directly to oxidized carbon. This enables fast kinetics for the breaking of both C–O and C O bonds. Complete reduction is observed in our simulation at T ≤ 600 K within 32 ps for a 28%-oxygen-coverage GO model.

First-principles electronic structure calculations were undertaken to clarify the observed n-type behavior of the hydrazine (N2H4) adsorbed on zigzag carbon nanotubes (CNTs). It was found that, only in the presence of moisture, the adsorption of the hydrazine will introduce occupied impurity states near the bottom of the conduction band of the N2H4/CNT system, leading to the n-type behavior. To gain further insight into the role played by the moisture, an extension of this study to other gases adsorbed on CNTs was also performed. Our results suggest that humidity could affect experimental measurements of responses of CNTs to adsorbed gases.

Substitution of all 10 3 d transition metal (TM) atoms in a [8, 0] zigzag single walled boron nitride nanotube (BNNT) has been investigated with density functional theory based methods. The TM atoms protrude to the exterior of the wall and may facilitate this site to react with an approaching molecular or atomic species. The substitution is site selective when the number of d electrons is less than five with major product of B-substituted BNNT. The substitution produces mixture of B- and N-substituted BNNT when the number of d electrons is larger than five. The doping of TM atoms induces certain impurity states within the band gap of the pristine BNNT, thereby reducing the band gap and affecting the conductivity of metal-doped BNNTs.

As candidates for hydrogen storage materials, Ti-doped pyracylenes, with a carbon atom replaced with a Ti atom, have been studied with density functional theory based method. Ti-doped pyracylene III with the Ti atom lying on a pentagon is the most stable isomer with substitutional energy of 4.73 eV/mol. Up to three H 2 molecules can be adsorbed on to the Ti atom through charge transfer and partially chemisorptions due to the partially filled d orbitals and positive charges on Ti. Totally seven H 2 molecules can be adsorbed on Ti-doped pyracylenes with mixture of chemo- and physisorption. Charge polarization induced electrostatic attraction is one of the major driving forces for physisorption.

The electronic isomerization arising from the switch of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) has been investigated within density functional theory. The switch of the HOMO and LUMO changes the electronic structures, thus the physicochemical properties of isomers. The predicted geometry, infrared spectra, and electronic spectra of fullerenes investigated show significant change upon electronic isomerization.

The adsorption of a series of small gaseous molecules (O 2 , CO 2 , C 2 H 4 , C 2 H 2 , H 2 O, NH 3 ) on the metal center in Pt-doped (5, 5) armchair single-wall BN nanotubes (BNNTs) has been explored within density functional theory. For all these gases studied, the overall process of adsorption was found to be exothermic, where the affinity correlates with the nature of the molecule adsorbed. Charge transfer is an important factor in changing the conductivity of analyte–substrate system. The two kinds of Pt-doped BNNTs exhibit different sensitivity and selectivity to gas molecules. The electronic structure of these materials is strongly influenced by the presence of gases, hence, application of Pt-doped single-wall BNNTs as gas sensors was proposed to motivate experimental trial.

With respect to density functional predictions, TM–methylidynes (TM = Sc, Ti, V, and Cr) bind high-density hydrogen at ambient conditions. TM–methylidyne complexes can adsorb up to seven hydrogen molecules. The predicted maximal retrievable hydrogen storage density is 16.7 wt% for ScCH, a record high value so far, larger than the 16.0 wt% for TiCH, 13.2 wt% for VCH, and 13.0 wt% for CrCH. Dimerization and oligomerization of scandium–methylidyne lower the hydrogen storage capacity to 9.2 wt% for the dimer and to 7.9 wt% for the hexamer. These predictions provide useful guidance for designing novel hydrogen storage materials with optimal gravimetry and kinetics and for devising possible schemes by which the hydrogen/host material interactions can be manipulated.

Novel Pt-doped armchair (5, 5) single-walled BN nanotubes (BNNTs) have been studied within density functional theory (DFT). The Pt atom protrudes to the exterior of the sidewall and favors attack from an approaching molecule. The smaller energy gap for the Pt-doped BNNTs implies that their conductivity is higher than that of the pristine BNNT. The DFT predictions suggest a strong affinity of the Pt atom in BNNT towards hydrogen molecules. The binding energies of H 2 with Pt-doped BNNTs are in the optimal range for hydrogen storage. Up to two H 2 can be partially dissociated with weak chemisorption, which improves the hydrogen storage capacity.

The Ni bis-dithiolene complexes with D2h symmetry were predicted to be stable at B3LYP/6-311++G(d) level. The analyses of nature bond orbital and nucleus-independent chemical shift (NICS) at B3LYP/6-31G(d) and GIAO-B3LYP/6-31G(d) level revealed the aromatic character of the Ni bis-dithiolene complexes. The total isotropic NICS (NICSiso) at the ring center [NICS(0)iso] has main contribution from the molecular orbitals (MOs) within the molecular plane according to the analysis of canonical MO (CMO) contributions to NICS. The π MOs have large contribution to the NICSiso at 1 A above the ring center [NICS(1)iso]. Both analyses of CMO and nature local MO (NLMO) predict that the Ni–S σ bonds weaken the aromaticity of the Ni(S2C2H2) and Ni(bdt)2 complexes. The three d atomic orbitals with lone pair electrons of the Ni atom and the delocalized π bond among S–C–C–S have large contribution to the NICS(0)iso and NICS(1)iso in Ni(S2C2H2) and Ni(bdt)2 according to the analyses of NLMO. The C–C π bond has large contribution to the NICS(n)iso (n = 0 or 1) in Ni(S2C2H2)2, while the delocalized S–C π bond has large contribution to the NICS(n)iso (n = 0 or 1) in Ni(bdt)2.

The phosphorus analogues (phosphanyl ketones) of pyridones are shown by theory to exhibit qualitatively different structures. Energy minimum of meta-phosphanyl ketone is planar while the planar conformations of the ortho- and para-isomers are transition state. Analysis of the electron density using the electron localization function (ELF) rationalizes the structural differences. In these molecules, there are competitive effects on geometry due to the octet rule, electron delocalization, and pyramidality of the tri-coordinated nitrogen or phosphorus. A delicate balance determines the molecular conformations.

Structures and magnetic properties [nucleus independent chemical shifts (NICS)] of [M2(η5–P5)2] and [M(η5–P5)2] (M = Be, Mg, and Ca) are studied with density functional theory at B3LYP level using the 6-311+G(d, p) basis sets. The M 2 2 + and M2+ sandwich complexes with D5 symmetry are minima. The D5h and D5d symmetry conformations are saddle points on the flat potential energy surface. Analyses of molecular orbital correlation and binding energy for the two series of complexes reveal that the M–M bond is a weak σ covalent bond. In addition to electrostatic interactions, there are also covalent bonds between the M and the P 5 - ring. The M–M bond plays a dominant role in the stability of both series of complexes. The M–M and M–P5 bond strength decreases as M varies from Be to Ca. The P–P bond length in these complexes is slightly elongated with respect to that in P 5 - . The NICS computed with GIAO-B3LYP/6-311+G(d,p) indicates that the P5 rings in both series of complexes are aromatic, and the aromaticity decreases as M varies from Be to Ca. In these complexes, the NICS at the P5 ring center slightly decreases and it increases at the outer side of the P5 ring, thus resulting in the elongation of P–P bond and the significant flow of π-electron from the ring towards the bonding of the P5 ring with the M 2 2 + unit or M and leading to the strengthening of the M–P5 bonding. The dissected NICS of the P 5 - ring of these complexes shows that the large total NICS is mainly due to the P–P π bond contribution of the P5 ring. The NICS of the P–P π bond decreases as the metal varies from Be to Ca.

Some η5-cyclopentadienyl cobalt dithiolene complexes CpCoS2C2R2 have been optimized at B3LYP/6-311++G(d) level. The optimized geometries agree well with experiment. The analyses of nature bond orbital and nucleus-independent chemical shift (NICS) at B3LYP/6-311++G(d) and GIAO-B3LYP/6-311++G(d) levels reveal the aromatic character of the η5-cyclopentadienyl cobalt dithiolene complexes. However, their aromaticity is weaker than that of the isolated CoS 2 C 2 + 1 . There are two reasons for the change of heterocyclic aromaticity of the metal dithiolene in the η5-cyclopentadienyl cobalt dithiolene complexes with respect to that of the isolated CoS 2 C 2 + 1 . The better equalization of bond lengths in the isolated cation CoS 2 C 2 + 1 is the first reason. The other reason is that the contribution to the NICS from the metallic cobalt atom is much larger in the isolated cation CoS 2 C 2 + 1 . The planar character of cyclopentadienyl is destroyed slightly in the complexes. At the same time, the size of cyclopentadienyl (Cp) becomes bigger than the isolated Cp−1 and this is caused by the cobalt atom in the pentagon. The π-electron delocalization causes stronger aromaticity of the Cp in the complexes than that of the isolated Cp−1.

The equilibrium geometries, energies, harmonic frequencies, and nucleus-independent chemical shifts of the zinc sandwich, the half-sandwich, and the zinc–zinc ( Zn 2 2 + ) sandwich complexes are computed by B3LYP/6-311++G(d,p) within the density functional theory. The staggered [(η5-C5H5)2Zn2] (1A1, D5d) is the most stable minimum with higher binding energy and slightly stronger aromaticity than those of the η5- C 5 H 5 − (1A1, D5h). The eclipsed [(η5-C5H5)2Zn2] (1A1, D5h) is a transition state with a small ring rotation barrier. The Zn-containing half-sandwich complexes are minima while with different stabilities and aromaticity. Particularly, the [(η5-C5H5)Zn] (2A1, C5v) has larger binding energy with aromaticity slightly weaker than η 5 − C 5 H 5 − , this compound features a simple while bona fide monovalent zinc molecular compound. The Zn2+ sandwich complex, [Zn(η5-C5H5)2] (1A1, D5h and D5d), with aromaticity weaker than that of the slip–sandwich complex, is a saddle point on potential energy surface. The slip–sandwich complex, (η1-C5H5)Zn(η5-C5H5) (1A1, C1), with aromaticity close to that of η 5 − C 5 H 5 − (1A1, D5h), is a local minimum. Both the eclipsed and the staggered [(C5(CH3)5)2Zn2](C1) are aromatic with aromaticity close to that of [(η5-C5H5)2Zn2] (D5d). According to the analysis of molecular orbitals, the Wiberg bond indices, the magnitude of charge transfer, the total nucleus-independent chemical shifts distributions, and the nucleus-independent chemical shifts contribution distributions of various bonds manifests, the stabilities of all the Zn-containing sandwich, the half-sandwich, and the Zn 2 2 + sandwich complexes are accredited to both ionic electrostatic interactions and covalent binding, especially the ionic electrostatic interactions, between the metal center and the η 5 − C 5 H 5 − building blocks.

Using density functional theory and the semiempirical ZINDO method, we have investigated the equilibrium geometries, electronic spectra, and the second and third hyperpolarizabilities of C 74 and the metallofullerene Ca@C 74 . Theory predicts that Ca@C 74 has greater stability than C 74 and that the UV–Vis spectrum of Ca@C 74 shifts to the blue. Both species possess relatively large β μ values and thus are promising as nonlinear optical materials.

Boron nitrosyl was examined with DFT, MP2, CCSD(T), and CASSCF. Poor overlap of the atomic orbitals on boron with the molecular orbitals of NO causes an accidental near degeneracy of the highest occupied σ- and π-orbitals. A near degeneracy of three electronic states results. DFT locates all three electronic states but finds unstable solutions for the 3 Σ − and 3 Π linear isomers. CASSCF/6-311+G(3df) and MP2/6-311+G(2df) predict 3 Σ − and 3 Π isomers but do not locate the 3 A ″ bent structure. CCSD(T)/6-311+G(d), predicts the 3 A ″ bent isomer to be 1.7 and 4.2 kcal/mol lower than the 3 Σ − and 3 Π linear isomers, respectively.