Chemisorptions effect of oxygen on the geometries,electronic and magnetic properties of small size Nin (n = 1-6) clusters

The present study reports the effect of oxygen addition on small size Ni_n (n = 1-6) clusters in different spin states within the framework of linear combination of atomic orbital (LCAO) density functional theory (DFT) under spin polarized generalized gradient approximation (GGA) functional. Relative stabilities of the optimized clusters are discussed on the basis of the calculated parameters, such as, binding energy (BE), embedding energy (EE) and fragmentation energy (FE). Other parameters, like ionization potential (IP), electron affinity (EA), etc. show that though the additions of oxygen can affect the chemical properties of Ni_n clusters with an additional stability to Ni_nO. In most of the cases the magnetic moment of the stable isomers are geometry dependent for a particular size both in pure and oxidized clusters. Calculated magnetic moments of Ni_nO (n = 1-6) clusters reveal that the magnetic moment of ground state Ni₄O isomers in different geometries is same as in pure Ni₄ isomers. Present study also explains the cause of stable magnetic moment in Ni₄O cluster through the distribution of electrons in different orbitals.     

Energy gaps of graphene clusters: the first-principles calculations based on high-throughput screening

Abstract

With the enumeration of the triangular lattice fragments, we have systematically investigated the graphene clusters (C_nH_m, n = 14 – 24) with various sizes and shapes, whose structural stabilities and electronic properties are studied by the Hückel molecular orbital (HMO) method and the first-principles calculation. According to the formation energies, we show the structural stabilities of the clusters are closely related to the shape and size, as well as the chemical potential of hydrogen. The energy gaps obtained from the HMO method are in the same trend with the ones calculated by the first-principles calculations, indicating the effective screening of the gap minimum and maximum in a fast speed. There is a general decreasing of the energy gaps with the size increment due to the quantum confinement, meanwhile, the gaps are also highly dependent on the shape of the clusters for those with the same number of carbon atom.     

Ab initio investigations on planar (MgO)n clusters (n = 1–5) and their hydrogen adsorption behaviour

Ab initio calculations (B3LYP and PBE-D3) of the structures, stabilities, vibrational, electronic and hydrogen adsorption behaviour of (MgO)_n clusters are performed using 6-311+ + G(d,p) basis set. The planar (MgO)_n clusters are found to be global minima for n ≤ 3 and local minima for n = 4 and 5. In addition, we have also analysed global minimum structures of (MgO)₄ and (MgO)₅. The binding energies suggest that their stabilities increase successively. Vibrational frequencies and IR intensities further support the enhanced stability with an increase in the size of (MgO)_n clusters. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) surfaces are used to explain and discuss the electronic properties. Finally, we have demonstrated hydrogen storage capacity of (MgO)_n clusters, considering hydrogen adsorption on planar as well as global minimum (MgO)₄ and (MgO)₅ clusters. We have noticed that four and five H₂ molecules can be easily adsorbed by (MgO)₄ and (MgO)₅ clusters having adsorption energy of 0.13–0.14 eV with mass ratio of 4.76%. Thus, the present study is expected to motivate further the applications of small clusters for efficient hydrogen energy storage.     

Theoretical study on small clusters of BaTiO3 using DFT calculations

Using density functional theory with the generalised gradient approximation, the structural and electronic properties of small (BaTiO₃)_n (n = 1–4) clusters have been studied. All the analysed growth modes were observed to consist of the same unit block, which in turn is similar to the well-known (TiO₂)₂ cluster. The BaTiO₃ and (BaTiO₃)₂ systems were observed to adopt analogous geometries to the ground state of (TiO₂)_n clusters with C_s and D_2h symmetries, respectively. The calculated value of the energy gap for the studied (BaTiO₃)_n clusters tends to approach that observed for its tetragonal bulk BaTiO₃ counterpart when n ≥ 3 is considered; the same tendency is observed for the Ba–Ba, Ba–Ti, Ti–O and Ba–Ti interatomic distances. For all the (BaTiO₃)_n clusters, the structural characteristics of their respective isomers were explored.     

A theoretical study on H-bonding interactions in maleic acid: calculated 17O, 1H NMR parameters and QTAIM analysis

A theoretical study was carried out to examine intra- and intermolecular hydrogen bond (HB) properties in crystalline maleic acid (MA). We investigated geometries, ¹⁷O and ¹H nuclear magnetic resonance parameters of various MA clusters by means of M06 and B3LYP functionals using recently developed Jensen's polarisation-consistent basis sets, pcJ-n (n = 0, 1, 2, 3). Our results reveal that the calculated chemical shift isotropy, δ_iso, at the sites of ¹⁷O and ¹H nuclei depends markedly on the size of the basis set. Overall, convergence of the pcJ-n series is rather similar for both B3LYP and M06 functionals. An increase of δ_iso(¹⁷O) and δ_iso(¹H) in going from the pcJ-1 to the pcJ-3 basis set is a typical feature of the (MA)_1–3 clusters. The quantum theory of atoms in molecules (QTAIM) and energy decomposition analyses were also used to elucidate the interaction characteristics in the MA H-bonded network. According to QTAIM results obtained, it is concluded that strong HBs are more covalent in nature and weak HBs are mainly electrostatic interactions.     

A density functional study of chemical,magnetic and thermodynamic properties of small palladium clusters

Structural, chemical, magnetic and thermodynamic properties of palladium clusters Pd_n with n = 2–11 are studied using density functional methods. The average bond length, entropy, enthalpy and polarisability are observed to increase as the cluster grows in size. The binding energy per atom also increases with cluster size. Stability function and atom addition energy change predict that Pd₄, Pd₆ and Pd₉ are relatively more stable than their neighbouring clusters. Electron affinity, electronegativity and electrophilicity values suggest that larger clusters have stronger tendency to accept electrons, thereby supporting the relative stability of Pd₄ and Pd₆. Chemical hardness is also seen to decrease with cluster size, which suggests that large clusters are more prone to changes in their electronic structure. The magnetic properties of these clusters are reported.     

Electronic structure and stabilities of Ni-doped germanium nanoclusters: a density functional modeling study

The present study reports the geometry, electronic structure, growth behavior and stability of neutral and ionized nickel encapsulated germanium clusters containing 1–20 germanium atoms within the framework of a linear combination of atomic orbital density functional theory (DFT) under a spin polarized generalized gradient approximation. In the growth pattern, Ni-capped Ge_n and Ni-encapsulated Ge_n clusters appear mostly as theoretical ground state at a particular size. To explain the relative stability of the ground state clusters, variation of different parameters, such as average binding energy per atom (BE), embedding energy (EE) and fragmentation energy (FE) of the clusters, were studied together with the size of the cluster. To explain the chemical stability of the clusters, different parameters, e.g., energy gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO–LUMO gap), ionization energy (IP), electron affinity (EA), chemical potential (μ), chemical hardness (η), and polarizability etc. were calculated and are discussed. Finally, natural bond orbital (NBO) analysis was applied to understand the electron counting rule applied in the most stable Ge₁₀Ni cluster. The importance of the calculated results in the design of Ge-based superatoms is discussed.

Architecture, electronic structure and stability of TM@Ge(n) (TM = Ti, Zr and Hf; n = 1-20) clusters: a density functional modeling

The present study reports the geometry, electronic structure and properties of neutral and anionic transition metal (TM = Ti, Zr and Hf)) doped germanium clusters containing 1 to 20 germanium atoms within the framework of linear combination of atomic orbitals density functional theory under spin polarized generalized gradient approximation. Different parameters, like, binding energy (BE), embedding energy (EE), energy gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO), ionization energy (IP), electron affinity (EA), chemical potential etc. of the energetically stable clusters (ground state cluster) in each size are calculated. From the variation of these parameters with the size of the clusters the most stable cluster within the range of calculation is identified. It is found that the clusters having 20 valence electrons turn out to be relatively more stable in both the neutral and the anionic series. The sharp drop in IP as the valence electron count increases from 20 to 21 in neutral cluster is in agreement with predictions of shell models. To study the vibrational nature of the clusters, IR and Raman spectrum of some selected TM@Ge_n (n = 15,16,17) clusters are also calculated and compared. In the end, relevance of calculated results to the design of Ge-based super-atoms is discussed.     

A theoretical study of cooperative and anticooperative effects on hydrogen-bonded clusters of water and the cyanuric acid

Ab initio and density functional calculations are used to analyse the interaction between a molecule of the cyanuric acid and one, two and three molecules of water at B3LYP/6-311++ G(d,p) and MP2/6-311++ G(d,p) computational levels. Also, the cooperative effect (CE) in terms of the stabilisation energy of clusters is calculated and discussed. Depending on the geometry of clusters under study, the cooperative, non- or anti-CE was found with an increasing cluster size. Red shifts of N–H and C = O stretching frequencies illustrate a good dependence on the CE. The atoms in molecules theory is used to analyse the CE on topological parameters.     

A semi-empirical conformational analysis of the interaction of n-alkanols with dipalmitoylphosphatidylcholine

The interaction of a homologous series of saturated aliphatic n-alkanols (containing 1–13 carbon atoms) with dipalmitoylphosphatidylcholine was studied by a semi-empirical conformational analysis. The minimal conformational energy of the isolated molecule at the hydrocarbon-water interface was calculated as the sum of the contributions resulting from the Van der Waals, torsional, electrostatic and transfer energies. From the conformers of minimal energies were calculated the hydrophilic-hydrophobic balance, the distance between hydrophilic and hydrophobic centres and the energies of interaction between homologous alkanols and between alkanols and lipids. Using these parameters, different modes of conformation, orientation and interaction of n-alkanols and dipalmitoylphosphatidylcholine were described. For methanol, ethanol and n-propanol, the gauche conformers were the most probable interacting only with the lipid polar heads. Only all-trans conformers were obtained for alkanols with longer acyl chains. n-Butanol to n-octanol form clusters in the lipid matrix. Longer n-alkanols are randomly distributed in the lipid layer. However, due to the increase in hydrocarbon chain-length, n-nonanol and higher alkanols have an interaction energy identical or superior to that found in a pure lipid monolayer, leading to a more ordered alkanol-lipid organization.     

New developments in first-principles excited-state dynamics simulations: unveiling the solvent specificity of excited anionic cluster relaxation and electron solvation

Charge-transfer-to-solvent excited iodide–polar solvent molecule clusters, [I^? (Solv)_n]^*, have attracted substantial interest over the past 20 years as they can undergo intriguing relaxation processes leading ultimately to the formation of gas-phase molecular analogues of the solvated electron. In this review article, we present a comprehensive overview of the development and application of state-of-the-art first-principles molecular dynamics simulation approaches to understand and interpret the results of femtosecond photoelectron spectroscopy experiments on [I^? (Solv)_n]^* relaxation, which point to a high degree of solvent specificity in the electron solvation dynamics. The intricate molecular details of the [I^? (Solv)_n]^* relaxation process are presented, and by contrasting the relaxation mechanisms of clusters with several different solvents (water, methanol and acetonitrile), the molecular basis of the solvent specificity of electron solvation in [I^? (Solv)_n]^* is uncovered, leading to a more refined view of the manifestation of electron solvation in small gas-phase clusters.     

Dielectric and electric properties of synthetic melanin: the effect of europium ions

Detailed studies on dielectric and electric properties of synthetic pirocatechol and indolederived melanin, pure and doped with Eu³⁺, have been performed, D.C. and a.c. electrical conductivity as well as dielectric permittivity and loss angle tg have been investigated. Activation energy of d.c. conductivity for the investigated temperature range (0°C3+ doped to the samples do not influence the values of activation energy, but the addition of Eu³⁺ ions decreases the conductivity values. On the basis of depolarization current curves the energy of trap level referred to Eu³⁺ has been calculated. It equals 0.58 eV for pirocatechol and 0.60 eV for indolemelanin.     

Carbon dioxide capture by planar (AlN)<Subscript>n</Subscript> clusters (<Emphasis Type="Italic">n</Emphasis>=3–5)

Searching for materials and technologies of efficient CO₂ capture is of the utmost importance to reduce the CO₂ impact on the environment. Therefore, the (AlN)_n clusters (n = 3–5) are researched using density functional theoretical calculations. The results of the optimization show that the most stable structures of (AlN)_n clusters all display planar configurations at B3LYP and G3B3 methods, which are consistent with the reported results. For these planar clusters, we further systematically studied their interactions with carbon dioxide molecules to understand their adsorption behavior at the B3LYP/6–311+G(d,p) level, including geometric optimization, binding energy, bond index, and electrostatic. We found that the planar structures of (AlN)_n (n = 3–5) can capture 3–5 CO₂ molecules. The result indicates that (AlN)_n (n = 3–5) clusters binding with CO₂ is an exothermic process (the capture of every CO₂ molecule on (AlN)_n clusters releases at least 30 kcal mol^-1 in relative free energy values). These analysis results are expected to further motivate the applications of clusters to be efficient CO₂ capture materials.     

Energetics,kinetics and dynamics of self-interstitial clusters in bcc tungsten

The configuration, slipping and rotation of self-interstitial atoms cluster along <111> crystal orientation with different sizes in a tungsten are investigated systematically with molecular dynamics. It is found that (I) the SIA clusters with high symmetry are always favoured; (II) the SIA clusters can undergo one-dimensional fast migration along <111> direction, and their migration barriers are no more than 0.07?eV, which is expected due to the strong interaction in the SIA clusters; (III) the rotation energy barriers of the SIA clusters are rather high and they are basically positively correlated with the size of the cluster. For example, the reorientation barrier is 0.66?eV for 1 SIA, 1.2–1.8?eV for SIA_n (2?≤?n?≤?5) clusters and over 2.7?eV for SIA_n (6?≤?n?≤?7) clusters. Compared with slipping of SIA clusters, is an infrequent event, especially for larger SIAs cluster, the vast majority SIAs cluster would have already recombination with vacancies or annihilates at surface and grain boundary through slipping before rotation, which explained that there are very low density of SIAs cluster found in the experiment.     

Global Potential Energy Minima of SPC/E Water Clusters without and with Induced Polarization Using a Genetic Algorithm

The global minimum potential energy structures of water clusters, (H₂O) _n , n = 2-14, have been calculated for the SPC/E (Simple Point Charge/Extended) model and a recent fluctuating charge version of the latter using a simple genetic algorithm. The SPC/E cluster geometries are in good agreement with previous TIP3P (Transferable Intermolecular Potential-3 Point) and TIP4P (Transferable Intermolecular Potential-4 Point) calculations as well as the interpretation of experimental measurements. In contrast to this, the polarizable version of the SPC/E model, which is based on the fluctuating charge approach, deviates rather strongly for n=6 with few exceptions. However, comparing the polarizable model to ab initio results for identical cluster geometries we find reasonable agreement for the magnitude of the average molecular dipole moment, the corresponding energy per molecule, and the average oxygen-oxygen distance as functions of n.Electronic Supplementary Material available.     

An insight into the structures,stabilities, and bond character of BnPt (n=1∼6) clusters

We perform a systematical investigation on the geometry, thermodynamic/kinetic stability, and bonding nature of low-lying isomers of B_nPt (n=1-6) at the CCSD(T)/[6-311+G(d)/LanL2DZ]//B3LYP/[6-311+G(d)/LanL2DZ] level. The most stable isomers of B_nPt (n=1-6) adopt planar or quasi-planar structure. B_nPt (n=2-5) clusters can be generated by capping a Pt atom on the B-B edge of pure boron clusters. However, For B₆Pt with non-planar structure, a single doped Pt atom significantly affects the shape of the host boron cluster. The dopant of the Pt atom can improve the stability of pure boron clusters. The valence molecular orbital (VMO), electron localization function (ELF), and Mayer bond order (MBO) are applied to gain insight into the bonding nature of B_nPt (n=2-6) isomers. The aromaticity for some isomers of B_nPt (n=2-6) is analyzed and discussed in terms of VMO, ELF, adaptive natural density partitioning (AdNDP), and nucleus-independent chemical shift (NICS) analyses. Results obtained from the energy and cluster decomposition analyses demonstrate that B₂Pt and B₄Pt exhibits as highly stable. Importantly, some isomers of B_nPt (n=2-5) are stable both thermodynamically and kinetically, which are observable in future experiment.     

Structure and vibrational frequencies of 6-chloro-8-thia-1,4-epoxybicyclo[4.3.0]non-2-ene: density functional theory study

The Fourier transform infrared (FT-IR) spectrum of 6-chloro-8-thia-1,4-epoxybicyclo[4.3.0]non-2-ene has been recorded in the region 4000–525 cm^? 1. The optimised geometry, frequency and intensity of the vibrational bands of the title compound have been calculated using the ab initio Hartree–Fock and the density functional theory method with 6-31G(d,p) and 6-311G(d,p) basis set levels. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FT-IR spectrum. The observed and the calculated frequencies are found to be in good agreement. The theoretical vibrational spectrum of the title compound were interpreted by means of potential energy distributions using VEDA 4 program.     

Seed and cone morphometric indicators: A new tool for the discrimination between the common Mediterranean pines Pinus halepensis Mill. and P. brutia Ten

Abstract

The two typical Mediterranean pines of Greece (Pinus halepensis Mill. and P. brutia Ten.) show a distinct, natural geographical distribution. However, in sites where they grow in sympatry (mainly due to extended reforestations), their morphological discrimination is not always easy. In the present study, three new morphometric indicators are introduced (at decreasing rank of reliability): (a) seed coat mass fraction, expressed as a percentage of the total seed mass (SM) (overall mean values 27.9 ± 0.5 (n = 160), and 58.0 ± 0.3 (n = 320) from 18 and 16 populations of Aleppo and East Mediterranean pine, respectively), (b) mean SM (16.70 ± 0.26 mg, n = 651, and 42.79 ± 0.61 mg, n = 425 from 18 and 16 populations of each of the two species, respectively) and (c) cone length/width ratio (2.20 ± 0.01, n = 651, and 1.77 ± 0.01, n = 606 from the same 18 and 16 populations, respectively). These three parameters are easily calculated, and constitute a reliable tool for the discrimination of the two pine species on the basis of their reproductive units (cones and seeds), provided that a minimal number of randomly collected samples is used for each indicator: 20 seeds for the measurement of seed coat mass fraction, about 1000 seeds for the estimation of mean SM, and 20 cones for the calculation of the cone length/width ratio. The functional implications of these adaptive traits are discussed.     

Valence orbital response to conformers of n-butane

Individual outer valence orbital responses to rotations of the C–C central bond of butane (C₄H₁₀) are explored on the torsional potential energy surface. Orbital ionization energies, topologies and momentum distributions for the four most significant butane conformation are presented, as snapshots of the conformational variations. The analysis is based on quantum mechanically generated information from coordinate space and momentum space, a technique called dual space analysis (DSA). By comparison with experimental measurements of photo-electron spectra (PES) for energies and of electron momentum spectra (EMS) for energies and Dyson orbitals, we demonstrate that the individual outer valence orbitals of these conformers response differently to the rotations of the central C–C bond of n-butane. Orbital signatures of other higher energy conformations, such as orbitals la ₂ and 5a ₁ of conformation D (C_2v ), are identified. This finding indicates a co-existence of butane conformations, although the global minimum structure of anti-butane, A (C_2h ), is dominant. Orbital topology and electron charges redistribution during the transformation provide useful information on the chemical bonding and related chemical reactions.     

Prediction of digestible and metabolisable energy in soybean meals produced from soybeans of different origins fed to growing pigs

The objective of this experiment was to determine the digestible energy (DE) and metabolisable energy (ME) in 22 sources of soybean meal (SBM) produced from soybeans from different countries and subsequently to establish equations for predicting the DE and ME in SBM based on their chemical composition. The 22 sources of SBM were all processed in Chinese crushing plants, but the soybeans used originated from China (n = 6), the US (n = 6), Brazil (n = 7) or Argentina (n = 3). The basal diet was a corn-based diet and 22 additional diets were formulated by mixing corn and 24.3% of each source of SBM. The average DE and ME in SBM from China, the US, Brazil and Argentina were 15.73, 15.93, 15.64 and 15.90 MJ/kg and 15.10, 15.31, 14.97 and 15.42 MJ/kg, respectively, and no differences among countries were observed. From a stepwise regression analysis, a series of DE and ME prediction equations were generated. The best-fit equations for SBM were DE = 38.44–0.43 crude fibre ?0.98 gross energy +0.11 acid detergent fibre (R² = 0.67, p < 0.01) and ME = 2.74 + 0.97 DE ?0.06 crude protein (R² = 0.79, p < 0.01). In conclusion, there were no differences in the DE and ME of SBM among the different soybean sources used in this experiment. The DE and ME of SBM of different origin can be predicted based on their chemical composition when fed to growing pigs.