Electronic and magnetic properties of small RhnCa (n = 1–9) clusters: A DFT study

The equilibrium geometries, relative stabilities, electronic and magnetic properties of small Rh_nCa (n = 1–9) clusters have been investigated by DFT calculations. The obtained results show that the three‐dimensional geometries are adopted for the lowest‐energy Rh_nCa clusters, and the doped Ca atom prefers locating on the surface of the cluster. Based on the analysis of the second‐order difference of energies, fragmentation energies and the HOMO‐LUMO energy gaps, we identify that the Rh₄Ca, Rh₆Ca, and Rh₈Ca clusters are relatively more stable than their neighboring clusters, and the doping of Ca enhances the chemical reactivity of the pure Rh_n clusters, suggesting that the Rh_nCa clusters can be used as nanocatalysts in many catalytic reactions. The magnetic moment for these clusters is mostly localized on the Rh atoms, and the doping Ca atom has no effect on the total magnetic moment of Rh_nCa clusters. The partial density of states, VIP, VEA, and η of these clusters in their ground‐state structures were also calculated and discussed. © 2015 Wiley Periodicals, Inc.     

Search for the global minimum structures of AlB3H2n (n = 0 − 6) clusters

The global minimum structures of AlB₃H_2n (n = 0–6) clusters are determined using the stochastic search method at the B3LYP/6–31G level of theory. These initially specified geometries are recalculated using B3LYP and CCSD(T) methods using the 6–311++G^** basis set. The structural and electronic properties of the two lowest‐lying isomers are presented. The structural parameters obtained for aluminum borohydride are compared with the experimental and theoretical results. The H₂ fragmentation energies of the most stable isomers are investigated. Chemical bonding analyses for the global minimum of AlB₃H_2n (n = 0–6) clusters are performed using the adaptive natural density partitioning method. © 2014 Wiley Periodicals, Inc.     

Electronic,bonding, and optical properties of 1d [CuCN]n (n = 1–10) chains, 2d [CuCN]n (n = 2–10) nanorings,and 3d [Cun(CN)n]m (n = 4, m = 2, 3; n = 10, m = 2) tubes studied by DFT/TD‐DFT methods

The electronic, bonding, and photophysical properties of one‐dimensional [CuCN]_n (n = 1–10) chains, 2‐D [CuCN]_n (n = 2–10) nanorings, and 3‐D [Cu_n(CN)_n]_m (n = 4, m = 2, 3; n = 10, m = 2) tubes are investigated by means of a multitude of computational methodologies using density functional theory (DFT) and time‐dependent‐density‐functional theory (TD‐DFT) methods. The calculations revealed that the 2‐D [CuCN]_n (n = 2–10) nanorings are more stable than the respective 1‐D [CuCN]_n (n = 2–10) linear chains. The 2‐D [CuCN]_n (n = 2–10) nanorings are predicted to form 3‐D [Cu_n(CN)_n]_m (n = 4, m = 2, 3; n = 10, m = 2) tubes supported by weak stacking interactions, which are clearly visualized as broad regions in real space by the 3D plots of the reduced density gradient. The bonding mechanism in the 1‐D [CuCN]_n (n = 1–10) chains, 2‐D [CuCN]_n (n = 2–10) nanorings, and 3‐D [Cu_n(CN)_n]_m (n = 4, m = 2, 3; n = 10, m = 2) tubes are easily recognized by a multitude of electronic structure calculation approaches. Particular emphasis was given on the photophysical properties (absorption and emission spectra) of the [CuCN]_n chains, nanorings, and tubes which were simulated by TD‐DFT calculations. The absorption and emission bands in the simulated TD‐DFT absorption and emission spectra have thoroughly been analyzed and assignments of the contributing principal electronic transitions associated to individual excitations have been made. © 2015 Wiley Periodicals, Inc.     

Theoretical study of the stability and properties of magic numbers (m = 5, n = 2) and (m = 6, n = 3) of bimetallic bismuth‐copper nanoclusters; Bim Cun

Inspired by the experimental discovery of magic numbers we present a first study using density functional theory for the structure and properties of neutral and cationic Bi₆Cu₃ and Bi₅Cu₂ clusters. Our results confirm predictions based on Wade's rules. The closed electron shells, characteristic of cationic clusters help impose enhanced stability, while also complying with Wade's rules. Charge distribution analysis, as well as electrostatic potential maps show that in almost all cases, Bi atoms donate charges to Cu atoms. According to the analysis of condensed Fukui indices, Cu atoms inside both clusters are not reactive. Contrastingly, Bi atoms are reactive and may be targeted by different types of attack. This study of the electronic properties may thus help to determine experimental strategies with the capacity to enhance the synthesis of catalysts.     

Theoretical investigation of LaC3n+ (n = 0, 1, 2) clusters by density functional theory

LaC₃ⁿ⁺ (n=0, 1, 2) clusters have been studied using B3LYP (Becke 3-parameter–Lee-Yang-Parr) density functional method. The basis set is Dunning/Huzinaga valence double zeta for carbon and [2s2p2d] for lanthanum, denoted LANL1DZ. Four isomers are presented for each cluster; two of them are edge binding isomers with C_2v symmetry, the other two are linear chains with C_∞v symmetry. Meanwhile, two spin states for each isomer, that is, singlet and triplet for LaC₃⁺, doublet and quartet for LaC₃ and LaC₃²⁺, respectively, are also considered. Geometries, vibrational frequencies, infrared intensities, and other quantities are reported and discussed. The results indicate that at some spin states; the C_2v symmetry isomers are the dominant structures, while for the other spin states, linear isomers are energetically favored. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 301–307, 1998     

Lanthanide metals in the boron cages: Computational prediction of M@Bn (M = Eu,Gd; n = 38, 40)

Endohedral metalloborofullerenes (EMBFs) are novel boron analogues of the famous endohedral metallofullerenes (EMFs). Many EMBFs have been proposed by theoretical calculations thus far. However, in sharp contrast to EMFs, which trap most of the lanthanides with f electrons inside the cages, the corresponding lanthanide‐based EMBFs have never been reported. In this work, the encapsulation of Eu and Gd in the B₃₈ and B₄₀ fullerenes was studied by means of density functional theory calculations. Our results revealed that Gd@B₃₈(⁹A), Eu@B₄₀(⁸B₂), and Gd@B₄₀(⁷A″) all favor the endohedral configuration, and the electronic structures can be described as Gd³⁺@ , Eu²⁺@ , and Gd³⁺@ with jailed f electron spins. The large binding energies and sizable HOMO–LUMO gaps suggest that they may be achieved experimentally. They feature σ and π double aromaticity, and their excellent stabilities were confirmed by the Born–Oppenheimer molecular dynamics simulations. Finally, the infrared and UV/vis spectra were simulated to assist experimental characterization.     

Quantum chemical exploration of formaldehyde clusters (H2CO)n (n = 2–4)

Global exploration of equilibrium structures and interconversion pathways on the quantum chemical potential energy surface (PES) is performed for (H₂CO)n (n = 2–4) by using the Scaled Hypersphere Search‐Anharmonic Downward Distortion Following (SHS‐ADDF) method. Density functional theoretical (DFT) calculations with empirical dispersion corrections (D3) yielded comparable results for formaldehyde dimer in comparison with recent detailed studies at CCSD(T) levels. Based on DFT‐D3 calculations, trimer and tetramer structures and their stabilities were studied. For tetramer, a highly symmetrical S₄ structure was found as the most stable form in good accordance with experimentally determined tetramer unit in the formaldehyde crystal. © 2018 Wiley Periodicals, Inc.     

Structures and basicity of LiNOH (N = 1 − 5) species

LiOH is one of the strong bases among neutral molecules. What about hydroxides of small Li_n (n = 2 ? 5) clusters? The addition of a single atom to a cluster sometimes has dramatic effects on its reactivity. This fact motivated us to perform an ab initio MP2/6‐311++G(d, p) investigation on Li_nOH species (n = 1 ? 5). These Li_nOH species are stabilized by both ionic as well as covalent interactions, and are found to be stable against elimination of LiOH and OH. We have determined their gas and aqueous phase basicity by considering hypothetical protonation reactions. The calculated proton affinities of Li_nOH (n ≥ 2) suggest their reduced basicity as compared to LiOH by 50–100 kJ/mol. The NBO charges and the highest occupied molecular orbitals also reveal the electride and alkalide characteristics of Li₂OH and Li₃OH, respectively. © 2016 Wiley Periodicals, Inc.     

Structure and stability of Be6, Be,and Be clusters

The structure and stability of Be₆, Be, and Be clusters have been investigated at the B3LYP, B3PW91, and second‐order Møller–Plesset (MP2) levels of theory, along with the 6‐311G* basis set for neutral and cationic clusters and the 6‐311+G* basis set for anion clusters. CCSD(T)/6‐311+G* has also been used to calculate some neutral structure to find the most stable structure. Twelve Be₆, six Be, and eight Be isomers are identified. The distortion octahedron structure, pentagonal pyramids structure, and trapezoidal bipyramid structure are found to be the most stable structure on the neutral, cationic, and anionic surface, respectively. They are in agreement with the results reported previously. Natural bond orbital (NBO) analysis, molecular orbital (MO) pictures, and the nucleus independent chemical shift (NICS) values suggest aromatic of the neutral and cationic clusters and antiaromatic of the anionic cluster. The multi‐center σ bonds and delocalized π bonds play important role in the bonding of the beryllium clusters. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Synthesis,spectroscopic investigation,structural characterization and DFT calculation of the complexes [ReX2(N2COPh)(4-PhPyr)(PPh3)2] (X = Cl, Br)

The reactions of [ReX₂(η²-N₂COPh-N′,O)(PPh₃)₂] with 4-phenylpyrimidine have been performed. As a result, the two complexes [ReX₂(N₂COPh)(4-PhPyr)(PPh₃)₂] (X = Cl, Br) (4-PhPyr = 4-phenylpyrimidine), isostructural in the solid state, have been obtained. The crystal and molecular structures of ([ReCl₂(N₂COPh)(4-PhPyr)(PPh₃)₂])₂·CHCl₃ (1) and ([ReBr₂(N₂COPh)(4-PhPyr)(PPh₃)₂])₂·CHCl₃ (2) have been determined. The electronic structure of [ReCl₂(N₂COPh)(4-PhPyr)(PPh₃)₂] has been examined using the density functional theory (DFT) method. The spin-allowed electronic transitions of 1 have been calculated with the time-dependent DFT method, and the UV–Vis spectrum of [ReCl₂(N₂COPh)(4-PhPyr)(PPh₃)₂] has been discussed on this basis.     

Theoretical insight of nitric oxide adsorption on neutral and charged Pdn (n = 1–5) clusters

Density functional theory (DFT) calculations within the framework of generalized gradient approximation have been used to systematically investigate the adsorption of nitric oxide (NO) molecule on neutral, cationic, and anionic Pd_n (n = 1–5) clusters. NO coordinate to one Pd atom of the cluster by the end‐on mode, where the tilted end‐on structure is more favorable due to the additional electron in the π* orbital. On the contrary, in the neutral and cationic Pd₂ system, NO coordinates to the bridge site of cluster preferably by the side‐on mode. Charge transfer between Pd clusters and NO molecule and the corresponding weakening of N? O bond is an essential factor for the adsorption. The N? O stretching frequency follow the order of cationic > neutral > anionic. Binding energy of NO on anionic clusters is found to be greater than those of neutral and cationic clusters. © 2015 Wiley Periodicals, Inc.     

A Fukui function‐guided genetic algorithm. Assessment on structural prediction of Sin (n = 12–20) clusters

Theoretical studies are essential for the structural characterization of clusters, when it comes to rationalize their unique size‐dependent properties and composition. However, the rapid growth of local minima on the potential energy surface (PES), with respect to cluster size, makes the candidate identification a challenging undertaking. In this article, we introduce a hybrid strategy to explore the PES of clusters. This proposal involves the use of a biased initial population of a genetic algorithm procedure. Each individual in this population is built by assembling small fragments, according to the best matching of the Fukui function. The performance of a genetic algorithm procedure. The performance of the method is assessed on the PES exploration of medium‐sized Si_n clusters (n = 12–20). The most relevant results are: (a) the method converges at almost half of the time used by the canonical version of the GA and, (b) in all the studied cases, with the exception of Si₁₃ and Si₁₆, the method allowed to identify the global minimum (GM) and other important low‐lying structures. Additionally, the apparent deficiency of the proposal to identify the GM was corrected when a Si atom, or other low‐lying isomers, were considered to build the clusters. © 2017 Wiley Periodicals, Inc.     

Pentaatomic planar tetracoordinate silicon with 14 valence electrons: A large‐scale global search of (n + m = 4; q = 0, ±1, −2; X,Y = main group elements from H to Br)

Designing and characterizing the compounds with exotic structures and bonding that seemingly contrast the traditional chemical rules are a never‐ending goal. Although the silicon chemistry is dominated by the tetrahedral picture, many examples with the planar tetracoordinate‐Si skeletons have been discovered, among which simple species usually contain the 17/18 valence electrons. In this work, we report hitherto the most extensive structural search for the pentaatomic ptSi with 14 valence electrons, that is, (n + m = 4; q = 0, ±1, ?2; X, Y = main group elements from H to Br). For 129 studied systems, 50 systems have the ptSi structure as the local minimum. Promisingly, nine systems, that is, , HSiY₃ (Y = Al/Ga), Ca₃SiAl^?, Mg₄Si^2?, C₂LiSi, Si₃Y₂ (Y = Li/Na/K), each have the global minimum ptSi. The former six systems represent the first prediction. Interestingly, in HSiY₃ (Y = Al/Ga), the H‐atom is only bonded to the ptSi‐center via a localized 2c–2e σ bond. This sharply contradicts the known pentaatomic planar‐centered systems, in which the ligands are actively involved in the ligand–ligand bonding besides being bonded to the planar center. Therefore, we proposed here that to generalize the 14e‐ptSi, two strategies can be applied as (1) introducing the alkaline/alkaline‐earth elements and (2) breaking the peripheral bonding. In light of the very limited global ptSi examples, the presently designed six systems with 14e are expected to enrich the exotic ptSi chemistry and welcome future laboratory confirmation. © 2014 Wiley Periodicals, Inc.     

Structures and electronic properties of the small rubidium‐doped silicon RbSin (n = 1–12) clusters

The geometries, relative stabilities, and electronic properties of small rubidium‐doped silicon clusters RbSi_n (n = 1–12) have been systematically investigated using the density functional theory at the B3LYP/GENECP level. The optimized structures show that lowest‐energy isomers of RbSi_n are similar with the ground state isomers of pure Si_n clusters and prefer the three‐dimensional for n = 3–12. The relative stabilities of RbSi_n clusters have been analyzed on the averaged binding energy, fragmentation energy, second‐order energy difference, and highest occupied molecular orbital‐lowest unoccupied molecular orbital energy gap. The calculated results indicate that the doping of Rb atom enhances the chemical activity of Si_n frame and the magic number is RbSi₂. The Mulliken population analysis reveals that the charges in the corresponding RbSi_n clusters transfer from the Rb atom to Si atoms. The partial density of states and chemical hardness are also discussed. © 2014 Wiley Periodicals, Inc.     

Electronic and structural properties of Lin@Be2B8 (n = 1–14) and Lin@Be2B36 (n = 1–21) nanoflakes shed light on possible anode materials for Li‐based batteries

Systematic addition of Li atoms to the Be₂B₈ and Be₂B₃₆ backbones has been studied by density functional theory‐based calculations with the aim to investigate properties of interest on possible anode materials for Li‐based batteries. For the Be₂B₈Li_n (n = 1–8) and the Be₂B₃₆Li_n (n = 1–20) systems, lithium salts are dominant whereas a clear electride feature shows up for Be₂B₈Li_n (n = 9–14) and Be₂B₃₆Li₂₁. Addition of hydrogen radicals to these systems shows that the Be₂B₈Li₁₄ electride becomes a Be₂B₈Li₁₄H₂ hydride electride whereas Be₂B₃₆Li₂₁ leads to a Be₂B₃₆Li₂₁H salt. Moreover, for the addition of Li atoms to Be₂B₈ and the Be₂B₃₆ backbones, large values of the interaction and of the adsorption energy per Li atom, high specific capacity of Be₂B₈Li₁₄ and of Be₂B₃₆Li₂₁ (1860 and 1017 mAh g⁻¹, respectively) and low and flat voltage associated with lithiation have been found. Likewise, the considerable thermodynamic driving force (ΔG° = −29.66 kcal/mol) and the small energy barrier ( = 0.26 kcal/mol) associated with electron transfer in Be₂B₃₆Li₂₁ and Be₂B₃₆ species confirm that boron rich species have potential abilities to be used in the Li‐based battery. © 2018 Wiley Periodicals, Inc.     

Synthesis, characterisation of two hexa-iron clusters with {Fe2S2(CO)x} (x = 5 or 6) fragments and investigation into their inter-conversion

Reaction of a trithiol ligand, 2-(mercaptomethyl)-2-methylpropane-1,3-dithiol (H₃L), with tri-iron dodecacarbonyl in toluene produces two hexa-iron clusters (1 and 2). The two clusters are characterised crystallographically and spectroscopically. NMR spectroscopy reveals that the cluster 2 exists in two conformations in equilibrium 2_anti ⇔ 2_syn and the equilibrium constant K_eq = 0.55 under CO atmosphere. In the cluster 2, the central {Fe₂S₂(CO)₆} sub-unit is flanked by two identical {Fe₂S₂(CO)₆} satellite sub-units through thiolate linkages whereas one of the thiolate linkages can further form Fe-S bond with the proximal Fe atom in one of the two satellite sub-units to produce the cluster 1 by expelling one CO. This conversion can be entirely reversed by continuously purging CO through the solution of the cluster 1. As suggested by DFT calculations, the conversion features a key step, the rotation of the Fe_prox(CO)₃ to expose a vacant site for exogenic ligand binding (the S atom from the central sub-unit in this case) with concomitant switch for one of the three CO ligands in the unit of Fe_prox(CO)₃ from terminal to bridging orientation. The conversion from the clusters 1-2 involving one CO uptake is much faster than its reverse process since the latter is an endergonic process characterised by large reaction barriers, as revealed by the DFT calculations.     

Theoretical investigation of the structures and spectroscopic properties of (H2O4)n (n = 1–4) clusters

Density functional theory and ab initio calculations were performed to elucidate the hydrogen interactions in (H₂O₄)_n (n = 1–4) clusters. The optimized geometries, binding energies, and harmonic vibrational frequencies were predicted at various levels of theory. The trans conformer of the H₂O₄ monomer was predicted to be the most stable structure at the CCSD(T)/aug‐cc‐pVTZ level of theory. The binding energies per H₂O₄ monomer increased in absolute value by 9.0, 10.1, and 11.8 kcal/mol from n = 2 to n = 4 at the MP2/cc‐pVTZ level of theory (after the zero‐point vibrational energy and basis set superposition error corrections). This result implies that the intermolecular hydrogen bonds were stronger in the long‐chain clusters, that is, the formation of the longer chain in the (H₂O₄)_n clusters was more energetically favorable.