Ground-state Structure Research Articles

Density functional study on highly energetic organic azides with empirical formula Cn(N3)m

AbstractThe structural, electronic, and thermodynamical properties of Cn(N3)m (n = 1–7) (m = 4, 6) organic azides have been investigated using Density Functional Calculations. The ground state structures of organic azides were compared with CnHm (n = 1–7) (m = 4, 6) cumulenes which shows their higher relative stability. The stability and reactivity of organic azides were analyzed by calculating the HOMO‐LUMO gap, binding energies, and harmonic frequencies of the azides. The binding energy and formation energy of Cn(N3)m (n = 1–7) (m = 4, 6) organic azides suggest their energetic stability. The structural analysis of the azide group in Cn(N3)m (n = 1–7) (m = 4, 6) organic azide shows a tendency to stabilize at a maximum separation between functional azide groups. Ionization potential, electron affinities, and global hardness have been computed for Cn(N3)m (n = 1–7) (m = 4, 6) organic azides and the odd–even alternation rule was observed. The molecular dynamic simulation performed at 300 K for 1 fs confirms organic azide's structural stability at room temperature, except for C4(N3)4, and the members of their family can be synthesized.

A computational investigation of twelve phenylurea herbicides including photoexcitation and structural relaxation

Phenylurea herbicides are widely used to control unwanted plant growth, but can linger in the environment. Photodegradation is a key mechanism by which these compounds can be transformed. This paper investigates the direct photoabsorption and relaxation of twelve phenylurea compounds (chlorbromuron, chlortoluron, diuron, fenuron, fluometuron, isoproturon, linuron, methiuron, metobromuron, metoxuron, monolinuron, monuron) using density functional theory. Ground state structures are optimized at the B3LYP-D3/def2-SVP level of theory and excited states are computed using CAM-B3LYP-D3/def2-SVPD. These molecules are found to be mostly planar and structurally similar in the ground state, with the exception of methiuron which has a significant distortion. The vertical excitation energies are affected by the presence of halogen substituents, and trends in the relaxation of these states are observed. Specifically, halogenated compounds generally have a local excited state minimum corresponding to a stretched carbon-halogen bond, phenylureas containing a methoxy group on the nitrogen have a local minimum corresponding to a twisted urea group and/or a minimum corresponding to the breaking of the nitrogen–oxygen bond between the urea and the methoxy group. The results are discussed in the context of known photodegradation mechanisms for this class of compounds.

First principles investigation on optoelectronic and thermoelectric response of nitrides cadmium novel zintl compounds AB2C2 (A=Mg, Ca, Sr, Ba; B = Cd and C= N)

Novel materials for high efficiency advance devices are critical to investigate. Zintl compounds are widely explored in the recent years because of their direct narrow band gaps, higher optical conductivity and figure of merit required for optimal-optoelectronic and thermoelectric response respectively. Thus, in the current study, the structural, electronic, optical and thermoelectric properties of nitrides cadmium novel Zintl compounds AB2C2 (A=Mg, Ca, Sr, Ba; B=Cd and C= N) having trigonal structure are studied by full potential linearized augmented plane wave method based on density functional and Boltzmann transport theory. The main objective of this project is to provide novel thermo electrical data on Cd-based Zintl compounds, such as nitride cadmium-based compounds. To get the desire results, the exchange correlations with generalized gradient approximation were used to obtain the ground state structure parameters in these compounds. The computed lattice parameters and c/a -ratio increase from the top to down while the bulk-modulus B(GPa) decreases from top to bottom. The modified versions of the Beck-Johnson potential (TB-mBJ) predict that CaCd2N2, SrCd2N2, BaCd2N2 and MgCd2N2 compounds are semiconductors with narrow band gap of 0.18 eV, 0.21 eV, 0.84 eV and 0.07 eV respectively. Based on the optical properties a deep analysis of dielectric constant, refractive index, reflectivity and optical conductivity were carried. Across the entire temperature range, all the compounds exhibit a positive Seebeck coefficient, indicating P-type conduction. The direct energy band gap nature of these compounds with high conductivity in the visible region shows their suitability for optical applications. Also, the figure of merit of these compounds is close to unity which also speaks about the high efficiency for thermoelectric applications.

Substrate Doping and Defect Influence on P-Rich InP(001):H Surface Properties

Density-functional theory calculations on P-rich InP(001):H surfaces are presented. Depending on temperature, pressure and substrate doping, hydrogen desorption or adsorption will occur and influence the surface electronic properties. For p-doped samples, the charge transition levels of the P dangling bond defects resulting from H desorption will lead to Fermi level pinning in the lower half of the band gap. This explains recent experimental data. For n-doped substrates, H-deficient surfaces are the ground-state structure. This will lead to Fermi level pinning below the bulk conduction band minimum. Surface defects resulting from the adsorption of additional hydrogen can be expected as well, but affect the surface electronic properties less than H desorption.

Analogies between photochemical reactions and ground-state post-transition-state bifurcations shed light on dynamical origins of selectivity.

Revealing the origins of kinetic selectivity is one of the premier tasks of applied theoretical organic chemistry, and for many reactions, doing so involves comparing competing transition states. For some reactions, however, a single transition state leads directly to multiple products, in which case non-statistical dynamic effects influence selectivity control. The selectivity of photochemical reactions-where crossing between excited-state and ground-state surfaces occurs near ground-state transition structures that interconvert competing products-also should be controlled by the momentum of the reacting molecules as they return to the ground state in addition to the shape of the potential energy surfaces involved. Now, using machine-learning-assisted non-adiabatic molecular dynamics and multiconfiguration pair-density functional theory, these factors are examined for a classic photochemical reaction-the deazetization of 2,3-diazabicyclo[2.2.2]oct-2-ene-for which we demonstrate that momentum dominates the selectivity for hexadiene versus [2.2.2] bicyclohexane products.

Determination of Ground State Structures of Snx - (x=21-35) Clusters.

In this work, an unbiased global search with a homemade genetic algorithm was performed to investigate the structural evolution and electronic properties of Snx - (x=21-35) clusters with density functional theory (DFT) calculations. All the ground-state structures for all these Snx - (x=21-35) clusters have been confirmed by the comparison of the experimental and simulated photoelectron spectra (PESs). It has been revealed that all Snx - (x=21-35) clusters are tricapped trigonal prism (TTP)-based structures consisting of two (for sizes x=21-28) or three (for x=29-35) TTP units, with the remaining atoms adsorbed on the surface or inserted between TTP units. The gradually decreasing HOMO-LUMO gaps indicate that these clusters are undergoing semiconductor-to-metal transformation. The average binding energies show that the structural stabilities of Snx - clusters are not as good as that of silicon and germanium clusters. It found that sizes x=23, 25, 29, 33 show high relative stability.

Mechanistic insights into the AIE properties of BF2 complexes of N-acetyl 2-aminobenzothiazoles as rotorless polyheteroaromatics

A series of four novel BF2 complexes of N-acetyl 2-aminobenzothiazoles featuring rigid rotorless polyheteroaromatic structures have been designed and synthesized. All of these compounds exhibited AIE properties with excellent solid-state fluorescence quantum yields up to 81.7%. Theoretical calculations revealed the characteristics of their ground-state structures and excitation processes. Their seemingly abnormal nonradiative decay in solutions was investigated from both direct vibrational relaxation and S0/S1 surface crossing perspectives by the two-channel model. The minimum energy conical intersection (MECI) located by SF-TDDFT method indicated that the CI is mainly induced by the deformation of the BF2 complex ring, leads to elevated energy level, and thus is not responsible for the fluorescence quenching. The potential energy curve (PEC) constructed along the distortion angle θ of BF2 complex ring showed that when θ reaches 50° (the dark-state region approaching MECI), the energy barrier is only 0.11 eV, suggesting that the deformed dark state could serve as an effective deactivation channel via ultrafast internal conversion (IC). Crystallographic analysis illustrated that the F atoms perpendicular to the polyheterocycle could effectively prohibit detrimental π-π stacking and enhance intermolecular interactions, thereby resulting in efficient solid-state emission.

Perovskite-based two-dimensional ferromagnet Sr<sub>2</sub>RuO<sub>4</sub> monolayer

At present, the research on two-dimensional (2D) ferromagnets is mainly concentrated in the field of van der Waals materials, while the successful preparation of strain-free freestanding 2D perovskite films provides a great opportunity for the design of 2D ferromagnets beyond van der Waals materials. Perovskite oxide SrRuO<sub>3</sub>, as a typical perovskite itinerant ferromagnet, has broad application prospects in many fields. In this paper, the lattice dynamics, ground-state structure, electronic and magnetic properties of its perovskite monolayer with formula Sr<sub>2</sub>RuO<sub>4</sub>, as well as the effect of external electric field, are studied by combining first-principles calculation, symmetry analysis and Monte Carlo simulation. The influence of the Hubbard parameter <i>U</i> is also revealed. The results indicate that the ground-state structure under all <i>U</i> values is the structural phase (space group <inline-formula><tex-math id="M2">\begin{document}$P4/mbm$\end{document}</tex-math></inline-formula>) generated by octahedral rotation distortion. Similar to the SrRuO<sub>3</sub> bulk, the ground-state phase of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer exhibits ferromagnetism, which is independent of the <i>U</i> value and thus robust. Density functional theory calculation with Hubbard parameter <i>U</i> predicts the ground-state phase of the monolayer to be a ferromagnetic half metal with out-of-plane easy-magnetization axis, while excluding the <i>U</i> parameter predicts the ground-state phase to be a ferromagnetic metallic state. The ferromagnetism mainly originates from the strong ferromagnetic exchange interaction between the nearest neighbor spin pairs. The simulated Curie temperature of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer is 177 K, which is close to the value (150 K) of its bulk phase. The out-of-plane electric field does not change the ground-state structure and ferromagnetism of the Sr<sub>2</sub>RuO<sub>4</sub> monolayer, but can significantly modulate its electronic and magnetic properties. When an external electric field exceeding 0.3 V/Å is applied, the system undergoes a transition from a ferromagnetic half-metal state to a ferromagnetic metallic state. This work indicates the potential application of Sr<sub>2</sub>RuO<sub>4</sub> monolayer in low-dimensional spintrnic devices, and provides a reference for the development of perovskite-based 2D ferromagnets and the realization of controlling 2D magnetism by electric field.

Structure of small yttrium monoxide clusters, chemical bonding, and photoionization: threshold photoionization and density functional theory investigations.

The photoionization (PI) spectra of small gas-phase yttrium monoxide clusters, YnO (n = 1-8), are investigated, and the adiabatic ionization energies are determined. The stable structures are obtained from density functional theory (DFT) calculations. The ground state structures are further confirmed by the CCSD(T) method. The PI spectra are calculated for these stable structures and are compared with the experimental PI spectra. The ground-state structures of the neutral and cation clusters are experimentally assigned with confidence on the basis of a favourable agreement between the experimental and calculated PI spectra. New structures are proposed for Y2O, Y6O, and Y8O compared to the previous literature. Y2O is a linear molecule in the ground state that was previously proposed as a C2v bent molecule. The YnO clusters become 3-dimensional from n ≥ 3. The O atom stays outside, bridging a triangular face of yttrium clusters. Chemical bonding between the yttrium and oxygen atoms is mostly ionic. The excess charge on the oxygen atom is around 1.4e-, transferred from the yttrium atoms bonded with it. Yttrium atoms are mostly covalently bonded. However, for the bigger clusters, free charges of both polarities appear on yttrium atoms that are not bonded with oxygen, indicating ionic interactions. Frontier orbitals consist of mainly delocalized 4d electrons with some 5s contributions, forming Y-Y bonding interactions, but with little contribution and zero contribution from the oxygen orbitals, regardless of the cluster size. The lost electron of YnO+ mostly comes from the 5s orbitals of all Y atoms in the cluster up to size n = 4, and then from 4d-5s hybrid orbitals from n ≥ 5, with the d contribution increasing with size. This is contrary to the previous view in the literature that photoionization occurs from a localized 4d orbital.

Ca n neutral clusters: a two-step G 0 W 0 and DFT benchmark.

Electronic and structural properties of calcium clusters with a varying size range of 2-20 atoms are studied using a two-step scheme within the GW and density functional theory (DFT) with generalized gradient approximation (GGA). The GGA overestimates the binding energies, optimized geometries, electron affinities, and ionization potentials reported in the benchmark. The ground-state structure geometry and binding energy were obtained from the DFT for the ground-state structure of each cluster. The binding energy of the neutral clusters of the calcium series follows an increasing trend, except for a few stable even and odd clusters. The electronic properties of the calcium cluster were studied with an all-electron FHI-aims code. In the G 0 W 0 calculation, the magic cluster Ca10 has relatively high ionization potential and low electron affinity. The obtained ionization potentials from the G 0 W 0 @PBE calculation showed that the larger cluster has less variation, whereas the electron affinities of the series have an increasing trend. The ionization potentials from the G 0 W 0 benchmark for the calcium cluster series have not yet been described in the literature.

Prediction of novel ground-state structures and analysis of phonon transport in two-dimensional GexSy compounds.

We conducted this study to explore the ground-state structures of two-dimensional (2D) variable-composition GexSy compounds, driven by the polymorphic characteristics of bulk germanium sulfides and the promising thermoelectric performance of 2D GeS (Pmn21). To accomplish this, we utilized the highly successful evolutionary-algorithm-based code USPEX in conjunction with VASP for total energy calculations, leading to the discovery of three previously unexplored structures of Ge2S (P2/c), GeS (P3̄m1), and GeS2 (P21/c). These 2D materials exhibit significantly lower formation energies compared to their reported counterparts. We thoroughly scrutinized the structural stability and subsequently analyzed their electronic structures. Our analysis reveals a nearly direct band gap of 0.12/0.84 eV with the PBE/HSE06 functional for 2D Ge2S and an indirect band gap for 2D GeS and GeS2. Their semiconducting nature highlights the crucial importance of lattice thermal conductivity (κl), which we determined by solving the Boltzmann transport equation for phonons. Importantly, we predict a room temperature κl value of 6.82 W m-1 K-1 for GeS, lower than its 2D orthorhombic counterpart. In the case of GeS2, we observed an anisotropic κl value of 16.95/10.68 W m-1 K-1 along the zigzag/armchair directions at 300 K, with an in-plane anisotropy ratio of 1.59, surpassing that of 2D IV-VI compounds. We delve into detailed discussions regarding the role of lattice anharmonicity, group velocities, phonon lifetimes, and three-phonon weighted phase space in the overall thermal conductivity analysis.

Mechanistic insights into diversified photoluminescence behaviours of BF2 complexes of N-benzoyl 2-aminobenzothiazoles.

Many BF2 complexes of heteroaromatics are well known for their dual-state emission (DSE) properties. However, AIE and ACQ effects have also been observed in certain cases. To date, no rational explanations have been proposed for these uncommon photoluminescence (PL) behaviours. The current research prepared four BF2 complexes of N-benzoyl 2-aminobenzothiazoles with diversified photoluminescence (PL) properties as model compounds and utilized quantum chemical calculation tools to address this issue. Theoretical calculations revealed that the electron-donating groups (EDGs) at the para-position of the exocyclic phenyl ring exert significant influence on their ground-state electronic structures and vertical excitation features. Potential energy curve (PEC) analysis showed that the exocyclic phenyl ring and NMe2 could not function as effective rotors due to elevated energy barriers. Only the NPh2 of BFBB-3 could spontaneously rotate ∼60° to induce the formation of an emissive twisted intramolecular charge transfer (TICT) state. The two-channel model involving both vibronic relaxation and S0/S1 surface crossing revealed that the drastic narrowing of the S1/S0 energy gap in the region approaching minimun energy conical intersection (MECI) led to the generation of a dark state in BFBB-1. The small energy barrier to access the dark-state region makes the resulting fast internal conversion a competitive channel for excited-state deactivation. In contrast, the presence of EDGs in BFBB-2 and 4 inhibits this pathway, thereby resulting in intense fluorescence emissions in solution. In addition, crystallographic analysis illustrated that the F atoms perpendicular to the polyheterocycle promoted a slipped face-to-face packing mode and enhanced intermolecular interactions. The efficiencies of their solid-state emissions are mainly affected by the degree of π-π overlaps.

Towards reliable and efficient modeling of [Cu2O2]2+-based compound electronic structures with the partially fixed reference space protocols.

This work reports a computationally efficient approach for reliable modeling of complex electronic structures based on [Cu2O2]2+ moieties. Specifically, we explore the recently developed partially fixed reference space (PFRS) protocol to minimize the active space size, taking into account the double d-shell effects. We show that the ground-state electronic structure of the core [Cu2O2]2+ model system is dominated by the d9/d10 occupations. The PFRS-crafted active spaces are further used to generate the reference wave functions for the multi-reference coupled cluster, configuration interaction, and multi-reference perturbation theory calculations. Specifically, we demonstrate that the bare [Cu2O2]2+ core can be modeled qualitatively using active spaces as small as CAS(2,2)PFRS. To obtain quantitative agreement with the reference DMRG(32,62)CI calculations, the CAS(4,4) has to be used in conjunction with the MRCCSD correction on top of it. This reliable and computationally efficient protocol is further used to model the electronic structure and properties of ammonia coordinated [Cu2O2]2+ complexes. Finally, based on the large amount of available experimental data regarding the oxo-peroxo equilibrium of [Cu2O2]2+-based systems, it is possible to formulate educated guesses regarding the effect of each experimental variable over each d-occupancy-specific state. With a large sample size of d-occupancy-specific state dependence with ligands and solvents, it should be possible to propose new ligands with specific d-occupancy and, therefore, oxidative properties based on the d-occupancy energy gaps of relatively low-cost calculations.

Theoretical study of long-range ordered vacancy distribution in two-dimensional boron structures

<sec>In a two-dimensional boron structure, the ordered high-concentration vacancy distribution can enhance structural stability and significantly modulates material properties. Based on recent experimental progress, herein we particularly focus on the two-dimensional boron structures with a striped distribution of hexagonal vacancies, in order to explore the formation of long-period boron structures.</sec><sec>Utilizing the structures of alloy generation and recognition (SAGAR) program developed by our group, we eliminate duplicate structures according to the structural symmetry to reduce computational cost. An effective model system is proposed to investigate the effect of vacancy distribution on the stability of the system, where the interactions between vacancies are utilized for estimating the total energy. By selecting structures with appropriate concentrations and combining first-principles calculations, the parameters in the model are fitted for different vacancy neighbor interactions, which can be further used to predict stable structures at various vacancy concentrations. The feasibility of model analysis is emphasized for structural screening, showing the good agreement between the parameterized model and the first-principles calculations.</sec><sec>Interestingly, under the same vacancy concentration, stable boron structures with different cell sizes exhibit distinct vacancy distributions, indicating a trend of long-period distribution for ground state structures. To address this phenomenon, when the stable candidate structures from the 1/6 series are dominant in number within the computable range and the changes in neighbor statistics can be clearly seen, we select the structures from this concentration series for detailed calculations.</sec><sec>The calculation results indicate that the convergence of the average energy is primarily influenced by the interaction between the fourth nearest neighbor and the sixth nearest neighbor. When considering only these two neighbors, the system energy changes with the increase of cell size as follows: the average energy of structures with a cell size being an even multiple of the minimum cell size keeps unchanged, while the average energy of structure with a cell size being an odd multiple of the minimum cell size gradually decreases, eventually converging to a stable value. When including the interactions between the ninth nearest neighbor and the tenth nearest neighbor, the average energy of structures with a cell size being an even times the minimum cell size also decreases gradually. The average energy decreases with oscillations, with the magnitude gradually diminishing and eventually stabilizing. This discovery reveals that the enhanced stability of long-period structures is attributed to the competitive interactions among different neighboring vacancies.</sec>

Structural evolution and electronic properties of anionic carbon-nitrogen clusters.

Carbon-doped nitrogen clusters have represented a fascinating area of materials science in recent years. However, achieving precise control of the doping level and distribution of carbon within nitrogen clusters is challenging. Advanced techniques are required to elucidate their exact structures and electronic properties. Here, we perform systematic structure searches of anionic carbon-doped nitrogen clusters by the Crystal structure AnaLYsis by Particle Swarm Optimization method combined with density-functional theory calculations. The ground state structures of CNn- (n = 4-16) clusters for each cluster size are determined. The structural evolution, photoelectron energy spectra, electronic properties, and chemical bonding modes of anionic CNn- (n = 4-16) clusters are discussed. The calculated results indicate that the two-dimensional planar geometry of the anionic CN6- cluster with the C1 symmetry exhibits robust stability. The molecular orbitals and the adaptive natural density partitioning calculations show that the high stability of the anionic CN6- cluster is attributed to the localized σ-bonding formed by the 2p orbitals of carbon and nitrogen atoms. The four delocalized π chemical bonds contribute to the stability of the anionic CN6- cluster, resulting in a stable ring geometry. The present results enrich the database of geometric structures of carbon-nitrogen clusters and provide valuable insights for the experimental synthesis and characterization of nitrogen-based clusters.

Ground state of Rydberg-dressed Bose gas confined in a toroidal trap

The experimental realization of Rydberg dressing technology in ultracold atomic systems provides another superior platform for studying novel states of matter and macroscopic quantum phenomena. In this work, based on the mean-field theory, we have investigated the ground-state phases of a two-component Bose–Einstein condensate with Rydberg interaction and confined in a toroidal trap. The effects of the Rydberg interaction and external potential, especially the Rydberg blockade radius, on the ground-state structure of such a system have been investigated in full parameter space. Our results show that the Rydberg blockade radius, which can be regarded as another controllable parameter, can be used to obtain a variety of ground-state phases. More interestingly, it is found that for weak Rydberg interactions, the Rydberg blockade radius breaks the spontaneous rotational symmetry of the system, leading to the formation of a discrete unit cell structure. For strongly interacting cases, it can be used to realize different orders of discrete rotational symmetry breaking.

COMPAS-3: a dataset of peri-condensed polybenzenoid hydrocarbons.

We introduce the third installment of the COMPAS Project - a COMputational database of Polycyclic Aromatic Systems, focused on peri-condensed polybenzenoid hydrocarbons. In this installment, we develop two datasets containing the optimized ground-state structures and a selection of molecular properties of ∼39k and ∼9k peri-condensed polybenzenoid hydrocarbons (at the GFN2-xTB and CAM-B3LYP-D3BJ/cc-pvdz//CAM-B3LYP-D3BJ/def2-SVP levels, respectively). The manuscript details the enumeration and data generation processes and describes the information available within the datasets. An in-depth comparison between the two types of computation is performed, and it is found that the geometrical disagreement is maximal for slightly-distorted molecules. In addition, a data-driven analysis of the structure-property trends of peri-condensed PBHs is performed, highlighting the effect of the size of peri-condensed islands and linearly annulated rings on the HOMO-LUMO gap. The insights described herein are important for rational design of novel functional aromatic molecules for use in, e.g., organic electronics. The generated datasets provide a basis for additional data-driven machine- and deep-learning studies in chemistry.

Transitional character of Nd-Dy (N=90) isotones in IBM model

The Interacting Boson Model is used to study the level structure of ground state, beta, and gamma bands in150Nd, 152Sm, 154Gd and 156Dy (N = 90) isotones. The energy ratios R_((I+2)⁄2) and R_(0_2⁄2_1 ) are compared to the predictions of U(5), SU(3), and X(5) symmetry. The calculated reduced transition probabilities as well as quadrupoles moments were compared to experimental data. IBM-1 investigates the properties of the potential energy surface to determine the nuclear shape of the Nd-Dy (N=90) isotones.

First principles study of the structure and properties of Nb-Sn alloys under high pressure

We conducted a systematic high-pressure study on the Nb-Sn system using first-principles calculations based on density functional theory. The USPEX software package was used to investigate the crystal structure of Nb-Sn alloys under pressures ranging from 0 to 30 GPa. As a result, five new ground-state structures for the Nb-Sn alloys were predicted: Pm-3_Nb7Sn, I4/mmm_Nb2Sn, P6422_NbSn2, P4/nmm_NbSn3 and Cmcm_NbSn3. Accordingtoourcalculatedresults, it is found that eight compounds are thermodynamically and dynamically stable in Nb-Sn system under different pressures. These compounds are: Pm-3_Nb7Sn, Pm-3n_Nb3Sn(A15), Fddd_NbSn2, I4/mmm_Nb2Sn, P6222_NbSn2, P6422_NbSn2, P4/nmm_NbSn3, and Cmcm_NbSn3. The calculations of electronic properties indicate that structures exhibit metallic behavior. In addition, the superconducting transition temperatures of Pm-3_Nb7Sn at atmospheric pressure is ∼5.15 K, and our results also suggest that the superconducting properties arises mainly from the coupling between Nb-4d electrons and phonons near the Fermi level.

Electronic structure of 1,3‐diphenyl‐2‐azaallenyl radical cation

AbstractQuantum chemical simulations were conducted to elucidate the electronic structure of the 2‐azaallenyl radical cation, a key intermediate in several [3 + 2]‐cycloadditions initiated by the oxidation of 2H‐azirine. We propose one additional Lewis structure in resonance with the commonly accepted two Lewis structures for the model system of 1,3‐diphenyl‐2‐azaallenyl radical cation, drawn from comprehensive theoretical data including molecular shape, bond order analysis, partial atomic charges, and spin densities. In addition to the ground state chemistry, the chemical structure of excited state species can be also understood with these three Lewis structures. Theoretical data imply that a newly suggested one mainly accounts for the ground state structure, and the excited state structure is better represented by the previously reported ones. Our claim is further bolstered by the prediction of the excited state geometries of the dicationic and neutral species. This research presents the extended set of Lewis structures for a better understanding electronic structure of 2‐azaallenyl radical cation.