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

The structural, electronic, and thermodynamical properties of C_n(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 C_nH_m (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 C_n(N₃)_m (n = 1–7) (m = 4, 6) organic azides suggest their energetic stability. The structural analysis of the azide group in C_n(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 C_n(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.     

Ab initio characterization of size dependence of electronic spectra for linear anionic carbon clusters C(n) (-) (n = 4-17)

In this article, we determine the ground‐state equilibrium geometries of the linear anionic carbon clusters C (n = 4–17) by means of the density functional theory B3LYP, CAM‐B3LYP, and coupled cluster CCSD(T) calculations, as well as their electronic spectra obtained by the multireference second‐order perturbation theory CASPT2 method. These studies indicate that these linear anions possess doublet ²∏_g or ²∏_u ground state, and the even‐numbered clusters are generally acetylenic, whereas the odd‐numbered ones are essentially cumulenic. The energy differences, electron affinities, and incremental binding energies of C chains all exhibit a notable tread of parity alternation, with n‐even chains being more stable than n‐odd ones. In addition, the predicted vertical excitation energies from the ground state to four low‐lying excited states are in reasonably good agreement with the available experimental observations, and the calculations for the higher excited electronic transitions can provide accurate information for the experimentalists and spectroscopists. Interestingly, the absorption wavelengths of the 1²∏_u/g ← X²∏_g/u transitions of the n‐even clusters show a nonlinear trend of exponential growth, whereas those of the n‐odd counterparts are found to obey a linear relationship as a function of the chain size, as shown experimentally. Moreover, the absorption wavelengths of the transitions to the higher excited states of C series have the similar linear size dependence as well. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Polynitrogen clusters containing five-membered rings

Possible structures of N₁₅ cluster were examined by ab initio (MP2) and density functional theory (DFT) methods with the 6-31G* basis set. Their stabilities were compared together with other polynitrogen clusters N_n (n = 8, 10–14) reported in the literature. The order of stability was made respectively according to even or odd numbers of the total nitrogen atoms in clusters. It is found that both for even-numbered clusters N_2n (n = 4–7) and odd-numbered clusters N_{2n + 1} (n = 5–7) the thermodynamically most stable isomers are all based on pentazole units; for each one of N_n (n = 8, 10–15) clusters, the more conjugated the five-membered ring the more stable is the isomer; and, the more side-chains the N₅ ring links the less stable is the isomer. Another finding is that the larger the cluster the less stable is the cluster for every series of clusters of (a) containing two five-membered rings with an even number of total nitrogen atoms [N₁₀ (D_2d), N₁₂ (C_2h), N₁₄ (C_2h)], (c) containing one five-membered ring and a side-chain with an even number of total nitrogen atoms [N₈ (C_S), N₁₀ (C_S), N₁₂ (C_S), N₁₄ (C_S)], (d) containing one five-membered ring and a side-chain with an odd number of total nitrogen atoms [N₁₁ (C_S), N₁₃ (C_S), N₁₅ (C_S)], (e) chain clusters with an even number of total nitrogen atoms [N₈ (C_2h), N₁₀ (C_2h), N₁₂ (C_2h), N₁₄ (C_2h)], and (f) chain clusters with an odd number of total nitrogen atoms [N₁₁ (C_2v), N₁₃ (C_2v), N₁₅ (C_2v)]. For another series of clusters with two five-membered ring units [N₁₁ (C₂), N₁₃ (C_2v), and N₁₅ (C_2v)] (series b) the N₁₃ (C_2v) shows the best stability. It is also found that the even-numbered nitrogen clusters are more stable than the odd-numbered ones in comparison of series (a) with (b), (c) with (d), and (e) with (f). © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Structures and energies of CnS (1 ≤ n ≤ 20) sulphur carbide clusters

C_nS (1 ≤ n ≤ 20) clusters have been investigated by means of the density functional theory. As a general rule, when 1 ≤ n ≤ 17 the energetically most favorable isomers are found to be the linear arrangement of nuclei (C_∞v) with the sulphur atom at the very end of the carbon chain. The electronic ground state is alternately predicted to be ¹∑⁺ for odd n or ³∑⁻ for even n with a conspicuous odd–even effect in the stability of these clusters. The C₁₈S cluster is predicted to have a S-capped monocyclic structure (¹A₁), but with a low barrier to linearity. On the other hand, C₁₉S and C₂₀S are unambiguously linear in the ¹∑⁺ and ³∑⁻ electronic ground states, respectively.     

Laser ablation synthesis of new gold phosphides using red phosphorus and nanogold as precursors. Laser desorption ionisation time‐of‐flight mass spectrometry

Gold phosphides show unique optical or semiconductor properties and there are extensive high technology applications, e.g. in laser diodes, etc. In spite of the various AuP structures known, the search for new materials is wide. Laser ablation synthesis is a promising screening and synthetic method. Generation of gold phosphides via laser ablation of red phosphorus and nanogold mixtures was studied using laser desorption ionisation time‐of‐flight mass spectrometry (LDI TOFMS). Gold clusters Au_m⁺ (m = 1 to ~35) were observed with a difference of one gold atom and their intensities were in decreasing order with respect to m. For P_n⁺ (n = 2 to ~111) clusters, the intensities of odd‐numbered phosphorus clusters are much higher than those for even‐numbered phosphorus clusters. During ablation of P‐nanogold mixtures, clusters Au_m⁺ (m = 1‐12), P_n⁺ (n = 2‐7, 9, 11, 13–33, 35–95 (odd numbers)), AuP_n⁺ (n = 1, 2–88 (even numbers)), Au₂P_n⁺ (n = 1‐7, 14–16, 21–51 (odd numbers)), Au₃P_n⁺ (n = 1‐6, 8, 9, 14), Au₄P_n⁺ (n = 1‐9, 14–16), Au₅P_n⁺ (n = 1‐6, 14, 16), Au₆P_n⁺ (n = 1‐6), Au₇P_n⁺ (n = 1‐7), Au₈P_n⁺ (n = 1‐6, 8), Au₉P_n⁺ (n = 1‐10), Au₁₀P_n⁺ (n = 1‐8, 15), Au₁₁P_n⁺ (n = 1‐6), and Au₁₂P_n⁺ (n = 1, 2, 4) were detected in positive ion mode. In negative ion mode, Au_m^– (m = 1–5), P_n^– (n = 2, 3, 5–11, 13–19, 21–35, 39, 41, 47, 49, 55 (odd numbers)), AuP_n^– (n = 4–6, 8–26, 30–36 (even numbers), 48), Au₂P_n^– (n = 2–5, 8, 11, 13, 15, 17), Au₃P_n^– (n = 6–11, 32), Au₄P_n^– (n = 1, 2, 4, 6, 10), Au₆P₅^–, and Au₇P₈^– clusters were observed. In both modes, phosphorus‐rich Au_mP_n clusters prevailed. The first experimental evidence for formation of AuP₆₀ and gold‐covered phosphorus Au₁₂P_n (n = 1, 2, 4) clusters is given. The new gold phosphides generated might inspire synthesis of new Au‐P materials with specific properties. Copyright © 2012 John Wiley & Sons, Ltd.     

Density functional study of carbon monoxide adsorption on small cationic,neutral, and anionic aluminum nitride clusters

CO adsorption on small cationic, neutral, and anionic (AlN)_n (n = 1–6) clusters has been investigated using density functional theory in the generalized gradient approximation. Among various possible CO adsorption sites, an N on‐top (onefold coordinated) site is found to be the most favorable one, irrespective of the charge state of the clusters. The adsorption energies of CO on the anionic (AlN)_nCO (n = 2–4) clusters are greater than those on the neutral and cationic complexes. The adsorption energies on the cationic and neutral complexes reflect the odd–even oscillations, and the adsorption energies of CO on the cationic (AlN)_nCO (n = 5, 6) clusters are greater than those on the neutral and anionic complexes. The adsorption energies for the different charge states decrease with increasing cluster size. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1−5)

The density functional theory (DFT) and the complete active space self‐consistent‐field (CASSCF) method have been used for full geometry optimization of carbon chains C_2nH⁺ (n = 1–5) in their ground states and selected excited states, respectively. Calculations show that C_2nH⁺ (n = 1–5) have stable linear structures with the ground state of X³Π for C₂H⁺ or X³Σ^? for other species. The excited‐state properties of C_2nH⁺ have been investigated by the multiconfigurational second‐order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low‐lying states in C_2nH⁺ (n = 1–5). Present results indicate that the predicted vertical excitation and emission energies of C_2nH⁺ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Supersymmetry approaches to the radial bound states of the hydrogen‐like atoms

Various structural possibilities for Al_nN and Al_nN₂ (n = 1–7) neutral and cationic isomers are investigated, using the density functional method of Becke's three‐parameter hybrid exchange functional with the Lee–Yang–Parr nonlocal correlation. Structural optimization and frequency analyses are performed with the basis of 6‐311+G(d) for both the neutrals and cations. The calculations predicted the existence of a number of previously unknown isomers (i.e., Al₅N₂ and Al₆N₂). The resulting geometries show that the nitrogen atom prefers to be trapped and not to be on the periphery. Frequency analyses indicate that the 3‐D Al₅N, which was previous proposed as the ground‐state structure, is in fact a first‐order stationary point with an imaginary frequency at 45i (a₂). The optimized ground‐state structure of Al₅N obtained in this work is a planar configuration with the symmetry of C_2v. The calculated adiabatic ionization potentials in their ground states showed that AlN, Al₂N, Al₃N, and Al₄N₂ clusters are more stable than any others in Al_nN and Al_nN₂ (n = 1–7) species, being consistent with the observed time‐of‐flight (TOF) signal intensities. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

GamN (m＝1～9)团簇结构与稳定性的量子化学研究

用密度泛函理论(DFT)的B3LYP方法, 在6-31G*水平上对Ga_mN (m＝1～9)团簇的几何构型、电子结构、振动频率等性质进行了理论研究. 给出了将Ga_mN团簇中化学键键型和成键数目的多少与团簇的稳定性相结合, 可以较快找到Ga_mN团簇基态结构的一种方法. 通过对基态结构的能量二次差分讨论, 得到m为奇数的Ga_mN团簇比m为偶数的稳定.     

Comprehensive understanding of size‐, shape‐, and composition‐dependent polarizabilities of SimCn (m,n = 1–4) clusters

We performed a comprehensive study of the size‐, shape‐, and composition‐dependent polarizabilities of Si_mC_n (m, n = 1–4) clusters on the basis of the density‐functional‐based coupled perturbed Hartree–Fock calculations. We found better correlations between the polarizabilities and both the binding energies (E_b) and change in charge distribution (Δq) than the energy gaps. The α values exhibit overall decreasing and increasing trends with increases in the E_b and Δq values, respectively. For isomers with the same E_b values and different polarizabilities, Δq can well explain the difference in polarizabilities. The π‐electron delocalization effect is the best factor for understanding the shape‐dependence. For a given m/n value, the linear clusters have an obviously larger polarizability than both the prolate and compact clusters, irrespective of the cluster size. We fit a quantitative expression [α = A ? (A ? B) × exp(?k(m/n))] to describe the composition‐dependent polarizabilities. © 2012 Wiley Periodicals, Inc.     

Density functional study of structural and electronic properties of AlnN (1 ≤ n ≤ 12) clusters

Low‐lying equilibrium geometric structures of Al_nN (n = 1–12) clusters obtained by an all‐electron linear combination of atomic orbital approach, within spin‐polarized density functional theory, are reported. The binding energy, dissociation energy, and stability of these clusters are studied within the local spin density approximation (LSDA) and the three‐parameter hybrid generalized gradient approximation (GGA) due to Becke–Lee–Yang–Parr (B3LYP). Ionization potentials, electron affinities, hardness, and static dipole polarizabilities are calculated for the ground‐state structures within the GGA. It is observed that symmetric structures with the nitrogen atom occupying the internal position are lowest‐energy geometries. Generalized gradient approximation extends bond lengths as compared with the LSDA lengths. The odd–even oscillations in the dissociation energy, the second differences in energy, the highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps, the ionization potential, the electron affinity, and the hardness are more pronounced within the GGA. The stability analysis based on the energies clearly shows the Al₇N cluster to be endowed with special stability. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

High Magnetic Moments in Manganese‐Doped Silicon Clusters

We report on the structural, electronic, and magnetic properties of manganese‐doped silicon clusters cations, Si_nMn⁺ with n=6–10, 12–14, and 16, using mass spectrometry and infrared spectroscopy in combination with density functional theory computations. This combined experimental and theoretical study allows several structures to be identified. All the exohedral Si_nMn⁺ (n=6–10) clusters are found to be substitutive derivatives of the bare Si_n+1⁺ cations, while the endohedral Si_nMn⁺ (n=12–14 and 16) clusters adopt fullerene‐like structures. The hybrid B3P86 functional is shown to be appropriate in predicting the ground electronic states of the clusters and in reproducing their infrared spectra. The clusters turn out to have high magnetic moments localized on Mn. In particular the Mn atoms in the exohedral Si_nMn⁺ (n=6–10) clusters have local magnetic moments of 4 μ_B or 6 μ_B and can be considered as magnetic copies of the silicon atoms. Opposed to other 3d transition‐metal dopants, the local magnetic moment of the Mn atom is not completely quenched when encapsulated in a silicon cage.     

Comparative DFT study of N2 and no adsorption on vanadium clusters Vn (n = 2–13)

Using gradient‐corrected density functional theory, we have comparatively studied the adsorption properties of diatomic molecules N₂ and NO on vanadium clusters up to 13 atoms. Spontaneous dissociation is found for N₂ adsorbing on V_n with n = 4–6, 12, and for NO with n = 3–12, respectively, whereas for the rest of the clusters, N₂ (NO) molecularly adsorbs on the cluster for all the possible sites. The incoming N₂ retains the magnetism of V_n except for V₂ and V₆ whose moments are quenched from 2 μ_B to zero. Consequently, the moments of V_nN₂ (n = 2–13) show even/odd oscillation between 0 and 1 μ_B. On the adsorption of NO, the magnetic moments of V_n with closed electronic shell are raised to 1 μ_B at n = 4, 8, and 10, and 3 μ_B at n = 12, whereas for open shell clusters, their magnetic moments increase for n = 5 and 9 and decrease for n = 2, 3, 5–7, 11, and 13 by 1 μ_B. These findings are rationalized by combinatory analysis from several aspects, for example, the geometry and stability of bare clusters, charge transfer induced by the adsorption, feature of frontier orbitals, and spin density distribution. © 2012 Wiley Periodicals, Inc.     

Exploration on the structure,stability, and isomerization of planar CnB5 (n = 1−7) clusters

The structures, stabilities, nature of bonding, and potential energy surfaces of low‐energy isomers of planar C_nB₅ (n = 1?7) have been systematically explored at the CCSD(T)/6‐311+G(d)//B3LYP/6‐311+G(d) level. Incremental binding energy (IBE) and second order energy difference (Δ²E) analyses demonstrate that C_nB₅ clusters with even n have relatively higher stability. The nature of bonding in these clusters is discussed based on valence molecular orbital (VMO), and Mayer bond order (MBO). Hückel (4n + 2) rule and nucleus‐independent chemical shift (NICS) values suggest that the ground states of C₃B₅, C₄B₅, and C₇B₅ have π aromaticity. VMO, electron localization function (ELF), adaptive natural density partitioning (AdNDP), and NICS analyses reveal the double aromaticity of C₃B₅ cation. CB₅ and C₃B₅ are stable both thermodynamically and kinetically based on isomerization analysis. In addition, the simulated IR spectra are expected to be helpful for future experimental studies of these clusters.     

Si_2C_(m-2)(m=4～15)团簇的结构与稳定性

用密度泛函理论(DFT)的B3LYP/6-31G*方法, 对Si2Cm-2(m = 4~15)团簇的几何构型、电子结构、振动频率等性质进行了研究, 讨论了化学键的特征和热力学稳定性, 比较了Si2Cm-2团中环状和线状结构的差异。结果表明, m = 4~13的团簇为线状结构, m=14~15的团簇为环状结构。在线状结构中, 随着m增大, 自旋多重度出现1、3交替变化, 并且Si原子倾向于在C链端部成键;环状结构中, C原子形成环状, 2个Si原子处于椭圆环状构型的两端。m 为奇数的Si2Cm-2团簇比m为偶数的更为稳定。     

A theoretical study of the dependence of the ASxSi6−x cluster structures and properties on composition

The effect of the composition ratio between arsenic and silicon atoms on the structures and properties of As_xSi_6?x (x = 0–6) have been systematically investigated using the density functional theory at the B3LYP/6‐311+G* level. The As_xSi_6?x clusters prefer substitutional rather than attaching structures; the Si‐rich clusters favor Si₆‐like structures, whereas the As‐rich clusters prefer As₆‐like structures. The As atoms locating at the framework may explain the difficulty of removal of arsenic impurities from polycrystalline silicon. In general, the average binding energies gradually decrease, implying the As_xSi_6?x clusters become increasingly unstable as x increases. Both the HOMO‐LUMO gaps and the As‐dissociation energies present a strong even–odd alternation, implying alternating chemical stability, with the even x members being more stable than the odd ones. The dissociation energies of an As atom from As_xSi_6?x are: 3.07, 2.84, 1.84, 2.52, 1.86, and 2.85 eV, for x = 1–6, respectively, and 3.80, 3.08, 2.64, 3.01, 2.93, 3.16 eV for Si (x = 0–5). These dissociation energy results should provide a useful reference for further experimental investigations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Stability,Infrared Spectra and Electronic Structures of (ZrO2)n(n=3-6)Clusters:DFT Study

The stability, infrared spectra and electronic structures of (ZrO₂)_n (n=3–6) clusters have been investigated by using density‐functional theory (DFT) at B3LYP/6‐31G* level. The lowest‐energy structures have been recognized by considering a number of structural isomers for each cluster size. It is found that the lowest‐energy (ZrO₂)₅ cluster is the most stable among the (ZrO₂)_n (n=3–6) clusters. The vibration spectra of Zr? O stretching motion from terminal oxygen atom locate between 900 and 1000 cm^?1, and the vibrational band of Zr? O? Zr? O four member ring is obtained at 600–700 cm^?1, which are in good agreement with the experimental results. Mulliken populations and NBO charges of (ZrO₂)_n clusters indicate that the charge transfers occur between 4d orbital of Zr atoms and 2p orbital of O atoms. HOMO‐LUMO gaps illustrate that chemical stabilities of the lowest‐energy (ZrO₂)_n (n=3–6) clusters display an even‐odd alternating pattern with increasing cluster size.     

Low‐dimensional hydrogen‐bonded structures in the 1:1 and 1:2 proton‐transfer compounds of 4,5‐dichlorophthalic acid with the aliphatic Lewis bases triethylamine,diethylamine, n‐butylamine and piperidine

The structures of the proton‐transfer compounds of 4,5‐dichlorophthalic acid (DCPA) with the aliphatic Lewis bases triethylamine, diethylamine, n‐butylamine and piperidine, namely triethylaminium 2‐carboxy‐4,5‐dichlorobenzoate, C₆H₁₆N⁺·C₈H₃Cl₂O₄⁻, (I), diethylaminium 2‐carboxy‐4,5‐dichlorobenzoate, C₄H₁₂N⁺·C₈H₃Cl₂O₄⁻, (II), bis(butanaminium) 4,5‐dichlorobenzene‐1,2‐dicarboxylate monohydrate, 2C₄H₁₂N⁺·C₈H₂Cl₂O₄²⁻·H₂O, (III), and bis(piperidinium) 4,5‐dichlorobenzene‐1,2‐dicarboxylate monohydrate, 2C₅H₁₂N⁺·C₈H₂Cl₂O₄²⁻·H₂O, (IV), have been determined at 200 K. All compounds have hydrogen‐bonding associations, giving discrete cation–anion units in (I) and linear chains in (II), while (III) and (IV) both have two‐dimensional structures. In (I), a discrete cation–anion unit is formed through an asymmetric R₁²(4) N⁺—H...O₂ hydrogen‐bonding association, whereas in (II), chains are formed through linear N—H...O associations involving both aminium H‐atom donors. In compounds (III) and (IV), the primary N—H...O‐linked cation–anion units are extended into a two‐dimensional sheet structure via amide–carboxyl N—H...O and amide–carbonyl N—H...O interactions. In the 1:1 salts (I) and (II), the hydrogen 4,5‐dichlorophthalate anions are essentially planar with short intramolecular carboxyl–carboxyl O—H...O hydrogen bonds [O...O = 2.4223 (14) and 2.388 (2) Å, respectively]. This work provides a further example of the uncommon zero‐dimensional hydrogen‐bonded DCPA–Lewis base salt and the one‐dimensional chain structure type, while even with the hydrate structures of the 1:2 salts with the primary and secondary amines, the low dimensionality generally associated with 1:1 DCPA salts is also found.     

Luminescence properties and optimized structural conformations of the S0, S1 and T1 states of a tetranuclear formamidinate complex based on AuI and AgI metal ions

N,N′‐Bis(pyridin‐4‐yl)formamidine (4‐pyfH) was reacted with Au^I and Ag^I metal salts to form a novel tetranuclear complex, tetrakis[μ‐N,N′‐bis(pyridin‐4‐yl)formamidinato]digold(I)disilver(I), [Ag₂Au₂(C₁₁H₉N₄)₂] or [Au_xAg_4–x(4‐pyf)₄] (x = 0–4), 1 , which is supported by its metallophilicity. Due to the potential permutation of the coordinated metal ions, six different canonical structures of 1 can be obtained. Complex 1 shows an emission at 501 nm upon excitation at 375 nm in the solid state and an emission at 438 nm upon excitation at 304 nm when dispersed in methanol. Time‐dependent density functional theory (TD‐DFT) calculations confirmed that these emissions can be ascribed to metal‐to‐ligand charge transfer (MLCT) processes. Moreover, the calculations of the optimized structural conformations of the S₀ ground state, and the S₁ and T₁ excited states are discussed and suggest a distorted planar conformation for the tetranuclear Au₂Ag₂ complex.     

Theoretical study of structure and vibrational properties of MgnOn (n = 3–10) clusters

The structure and harmonic vibrations of Mg_nO_n (n = 3–10) clusters have been investigated using density functional theory. All structures are found to be cumulenic D_nh rings (equal bonds, alternating angles), with one intense out‐of‐plane mode and three infrared (IR)‐active degenerate modes, of which the highest one is extremely intense and increases asymptotically to 1000 cm^?1 for n = 10 at the B3LYP/6‐311++G(2d,2p) level. Comparisons with C_2n clusters show that B_nN_n and Be_nO_n clusters, the structure and bonding type for the Mg_nO_n clusters are consistent with those of the C_2n (n = 3, 5, 7,…) clusters B_nN_n(n = 3–10) and Be_nO_n(n = 3–10) clusters. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007