Second Energy Difference Research Articles

Ab initio diffusion quantum Monte Carlo study of the structural and electronic properties of small Lithium-Chloride LinCl (0,1+) (n = 1–7) clusters

Superalkali metal clusters as the potential building blocks of nanostructured materials have excellent nonlinear optical properties. In the present study, the structural and electronic properties of small LinCl (0,1+) (n = 1–7) clusters are investigated by the diffusion Monte Carlo method for the first time. We calculate the total ground state energy, ionization potential, binding energy, dissociation energy, and second difference in energy. We also analyze the contribution of electron correlation effects to the electron properties of the clusters. The DMC results of ionization potentials are more consistent with the experimental values. In addition, there is an odd–even alternation phenomenon that Li3Cl, Li5Cl, and Li7Cl are more stable, while Li2Cl+, Li4Cl+, and Li6Cl+ are more stable. The successful application of the quantum Monte Carlo (QMC) method on the small LinCl (0,1+) (n = 1–7) clusters implies that QMC may serve as a feasible tool to investigate the electronic properties of other superalkli metal clusters.

A systematic study of structures, stability, and electronic properties of alloy clusters AlBen (n = 1–12): Comparison with pure beryllium clusters

The geometric structures, energetic and electronic properties of the AlBen (n = 1–12) clusters have been systemically studied by using the hybrid density functional theory [B3LYP] and coupled cluster [CCSD(T)] method. It is found that the impurity Al atom is externally bound to the host Ben framework and its maximum coordination number is six. Besides, the geometries of AlBen bear close resemblance to the minimum structures of Ben+1. The AlBe3 and AlBe8 clusters exhibit high relative stability among the AlBen clusters, which is reflected by the evolutions of average atomic binding energy, dissociation energy, second difference in energy, adsorption energy of Al, and HOMO-LUMO gap with cluster size. In comparison to the pure Ben+1 clusters, AlBen exhibit larger binding energy values, whereas they are more polarizable.

Structural properties, magnetism and reactivity of [formula omitted] nanoalloys

Nickel-iron nanoparticles are magnetic and reactive. Both properties depend on the relative concentration of nickel and iron, which noticeably affects certain catalytic reactions among other applications. Density Functional Theory calculations, in the generalized gradient approximation to exchange and correlation, were conducted for neutral and charged Ni13-xFex nanoalloys with the aim of obtaining, from a first principles perspective, a better understanding of how the atomic structure, chemical order, magnetic properties, and reactivity depend on the composition and charge state. The atomic and electronic structures were determined without symmetry constraints for low-energy isomers with an exhaustive scan of the structural, homotopic, and spin degrees of freedom. The relative stability was analyzed in terms of the excess energy and the second difference in energy; the global reactivity was assessed by means of DFT indicators like the electronegativity and chemical hardness; local reactivity within each nanoalloy was characterized through the condensed Fukui functions. Finally, the first stage of oxidation is explored for the most and less reactive of the investigated nanoalloys.

A Systematic Study of Structures, Stability, and Electronic Properties of Alloy Clusters Alben (N = 1–12): Comparison with Pure Beryllium Clusters

The geometric structures, energetic and electronic properties of global minima of the AlBe n ( n = 1–12) clusters have been systemically studied by using the hybrid density functional theory [B3LYP] and coupled cluster [CCSD(T)] methods. It is found that the impurity Al atom is externally bound to the host Be n framework and its maximum coordination number is six. Besides, the geometries of AlBe n bear close resemblance to either local or global minimum structures of Be n +1 . The AlBe 3 and AlBe 8 clusters exhibit high relative stability among the AlBe n clusters, which is reflected by the evolutions of average atomic binding energy, dissociation energy, second difference in energy, adsorption energy of Al, and HOMO-LUMO gap with cluster size. In comparison to the pure Be n +1 clusters, AlBe n exhibit larger binding energy values, whereas they are more polarizable.

Electronic and geometric stability of double titanium-doped silicon clusters

We performed the genetic algorithm (GA) incorporated with density functional theory (DFT) calculations to investigate the atomic and electronic properties of a series of Ti2Si n (n = 3 = –24) clusters. Comprehensive consideration on the formation energy, the second difference in cluster energy and the addition energy of Si to a Ti2Si n−1 cluster as well as the HOMO-LUMO gap, our results show that Ti2Si4 cluster is the most stable one in the series of clusters, followed by the Ti2Si13, Ti2Si21,Ti2Si15 and Ti2Si7 clusters, which can be understood by the combination of symmetry and electron shell filling rule. The silicon cage could be obviously enhanced by doping double Ti atoms making them promising nanoscale materials.

Theoretical Investigation on Molecular Structure and Electronic Properties of BxLiy Cluster for Lithium-Ion Batteries with Quantum ESPRESSO Program.

In this study, molecular structure and electronic properties of eleven BxLiy (x = 1–3, y = 1–3) clusters are examined using the Perdew, Burke and Ernezerhof (PBE) method in the Quantum ESPRESSO program. Three main groups, consisting of two atoms, three atoms and four atoms, are selected as the starting points. The stable configurations, their binding energies per atom (Eb), dissociation energy (ΔE), and the second difference in energy (Δ2E), HOMO-LUMO (HOMO: Highest Occupied Molecular Orbital LUMO: Lowest Occupied Molecular Orbital) gaps, total energy, frequency, force on atom, point group, bond length, density of state (DOS) and band structures are investigated for BxLiy (x = 1–3, y = 1–3) clusters. The results of binding energies (Eb), dissociation energy (ΔE) and the second difference in energy (Δ2E) show that BLi, BLi2 first isomer, BLi2 second isomer, B2Li2 first isomer, B2Li2 second isomer and BLi3 are the most stable among all 11 molecules of BxLiy (x = 1–3, y = 1–3). The stability of BxLiy (x = 1–3, y = 1–3) clusters depend on both the formation of geometrical structures on the number of Li atoms. As the number of Li atoms in the group increases, the stability of BxLiy clusters also increases. Within each group formation of geometrical structures, the stability of BxLiy clusters changes. It is observed that they may change the capability of chemical reactions in BxLiy clusters.

Structural and electronic properties of Gen and EuGen-1 nanoclusters: A full potential DFT study

In this work, the stability, structure and electronic properties of the nanoclusters of germanium (Gen) and europium atom doped germanium clusters (EuGen-1) with n=2 to 12, 15 and 20 were investigated. First, the stability of nanoclusters such as Gen and EuGen-1 was addressed using FHI-aims as a software package based on the density functional theory. Then the lowest-energy structures were selected for calculating the first vertical ionization with the symmetry adapted cluster-configuration interaction General-R (SAC-CI-General-R) method. The results of this research show that there is a good agreement between calculation and experiment ionization potential for Gen nanoclusters. Generally, the analyses of binding energies show that increasing the size of nanoclusters leads to more stability for nanoclusters. The most stable nanoclusters for EuGen can be created with exchanging the Eu atom in the most stable Gen+1 nanoclusters, but there is an exception for n=11 case. Here, the second difference in energy (∆2E) and gap energy are computed for the stable nanoclusters. The results of ionization energy and second difference in energy confirm that Ge7 and Ge10 also EuGe8 and EuGe10 have the most stability.

A quantum Monte Carlo study of the structural and electronic properties of small boron clusters [formula omitted][formula omitted

Using diffusion quantum Monte Carlo, density functional theory, and Hartree–Fock methods, we investigate the structural and electronic properties of small neutral boron clusters with up to 13 atoms. We determine the lowest-lying energy structures, total ground-state energy, binding energy, dissociation energy, resonance energy, and investigate the impact of electron correlation on the stability of the clusters. The obtained results show agreement with available experimental and theoretical results. Moreover, analysis of the dissociation energy, the second difference in energy, and the resonance energy indicates that the clusters B3, B4, B8, and B10 are relatively more stable.

Study on Atom Packing and Electrical Properties of Tin (n=2-10) Clusters with GA&DFTB Calculations

The researches of atom packing and electronic properties of titanium clusters are of great significance in producing highly pure Ti particles. The geometrical structures as well as electronic properties of Tin(n=2-10) clusters were obtained by using density functional tight binding (DFTB) simulations being combined with genetic algorithms (GA). The binding energy, the second differences in energy, HOMO-LUMO gap, and Mulliken populations were calculated and discussed. The results show that these Ti clusters containing three or less atoms have planar structures or a linear form, while those containing more than four atoms present three-dimensional geometries. There exist different packing structures including tetrahedron, octahedron, and decahedron. As the atom number increases in these clusters, the configures are formed by capping the atoms on the (111) facets of these clusters with octahedron and decahedron geometries. The binding for the electrons is stronger in the icosahedral cluster than that in those clusters having the other configurations. Mulliken populations present significant differences as the atom packing changes in these clusters.

A comparative study of structure, stabilities and electronic properties of neutral and cationic [AuSin]λ and [Sin+1]λ (λ = 0, +1; n = 1–12) nanoalloy clusters

Structure, stabilities and electronic properties of [AuSin]λ and [Sin+1]λ (λ = 0, +1; n=1-12) nanoalloy clusters are studied invoking Density Functional Theory methodology. To understand the chemical stability of the lowest energy structure of cluster, chemical parameters like, Binding Energy, Fragmentation Energy, Second Order Difference in Energy and HOMO-LUMO energy gap are studied with the variation of cluster size. The binding energy of neutral and cationic Sin+1 and AuSin clusters is gradually increasing along with the cluster size n. The second order difference in energy for pure Sin+1 and doped cluster AuSin shows an interesting odd-even alternation behavior. It is found that Si7, AuSi5, [Si5]+ and [AuSi7]+ are the most stable clusters. The HOMO-LUMO energy gap of neutral and cationic AuSin cluster is high as compare to their corresponding neutral and cationic Sin+1 cluster. It indicates that doping of Au atom enhances the energy gap of silicon clusters. The computed HOMO-LUMO gap of neutral and cationic AuSin clusters are in the range of 1.35–2.94 eV, which is suitable for microelectronics, optoelectronic devices and photovoltaics applications. Density Functional Theory based descriptors viz. Electronegativity, Hardness, Softness and Electrophilicity Index are also reported. The HOMO-LUMO energy gap of pure Si and doped cluster AuSin displays odd-even oscillation behavior as a function of cluster size, n. The close agreement between theoretical and experimental results supports and validates our computational analysis.

Quantum Monte Carlo study on the structures and energetics of cyclic and linear carbon clusters Cn ( n = 1,...,10)

Using fixed-node diffusion quantum Monte Carlo (DMC) simulation we investigate the structural properties and energetics of the linear and cyclic carbon clusters ${\mathrm{C}}_{n}$ for $n\ensuremath{\le}10$. We calculate the binding energy, the electron correlation energy, the dissociation energy, and the second difference in energy. We also present an analysis of the structural properties of the clusters. It is found that the bond lengths, binding energies, and dissociation energies obtained from the DMC calculations are in excellent agreement with the available experimental results. The electron-correlation contribution to the binding energy indicates that in the case of the linear isomers, the clusters of odd-number size are relatively more favored than their neighbors of even-number size, whereas for the cyclic isomers, we do not observe the oscillation pattern. In the range of cluster size under investigation, we find that the electron-correlation impact in the binding energy of the cyclic clusters is larger than that of the corresponding linear ones, varying from $30%$ to $40%$ of the binding energy values. The electron correlation is also essential to the stability of the clusters enhancing by up to $52%$ their dissociation energy. A comparative analysis of the dissociation energy and second difference in energy indicates that the linear isomers ${\mathrm{C}}_{3}$ and ${\mathrm{C}}_{5}$ are the most stable ones.

Theoretical investigation on the low-energy isomer identification, structural evolution, stability, and electronic properties of Al10–xBex (x = 1–9) nanoalloys

Numerous isomeric equilibrium structures have been identified for the Al10–xBex (x = 1–9) nanoalloy clusters by using the stochastic search procedure in combination with density functional theory calculations. The relative stability and various electronic properties of the lowest-energy Al10–xBex (x = 0–10) clusters have been systematically studied by using the B3LYP and CCSD(T) methods with the aug-cc-pVDZ basis set. The evolution of the binding energies, the second difference in energy, HOMO–LUMO gaps, vertical detachment energies, vertical ionization potentials, vertical electron affinities, and hardness with the increasing number of Be atoms in the most stable Al10–xBex (x = 0–10) clusters demonstrates that the global minimum of Al8Be2 cluster possesses a special stability. Thus, the electronic structure of the lowest-energy Al8Be2 cluster has been also detected in detail. In addition, it is found that the polarizabilities gradually decrease with increasing number of Be atoms, and the charges always transfer from Al to Be atoms in these nanoalloy clusters. We hope this work could provide helpful insight into the composition-dependent electronic properties of BeAl alloy at the nanoscale, serving as powerful guidelines for future experimental research.

First-principles study of MoS2 and MoSe2 nanoclusters in the framework of evolutionary algorithm and density functional theory

Evolutionary algorithm is combined with full-potential ab initio calculations to investigate conformational space of (MoS2)n and (MoSe2)n (n = 1–10) nanoclusters and to identify the lowest energy structural isomers of these systems. It is argued that within both BLYP and PBE functionals, these nanoclusters favor sandwiched planar configurations, similar to their ideal planar sheets. The second order difference in total energy (Δ2E) of the lowest energy isomers is computed to estimate the abundance of the clusters at different sizes and to determine the magic sizes of (MoS2)n and (MoSe2)n nanoclusters. In order to investigate the electronic properties of nanoclusters, their energy gap is calculated by several methods, including hybrid functionals (B3LYP and PBE0), GW approach, and Δscf method. At the end, the vibrational modes of the lowest lying isomers are calculated by using the force constants method and the IR active modes of the systems are identified. The vibrational spectra are used to calculate the Helmholtz free energy of the systems and then to investigate abundance of the nanoclusters at finite temperatures.

Application of a parallel genetic algorithm to the global optimization of medium-sized Au\u2013Pd sub-nanometre clusters

To contribute to the discussion of the high activity and reactivity of Au–Pd system, we have adopted the BPGA-DFT approach to study the structural and energetic properties of medium-sized Au–Pd sub-nanometre clusters with 11–18 atoms. We have examined the structural behaviour and stability as a function of cluster size and composition. The study suggests 2D–3D crossover points for pure Au clusters at 14 and 16 atoms, whereas pure Pd clusters are all found to be 3D. For Au–Pd nanoalloys, the role of cluster size and the influence of doping were found to be extensive and non-monotonic in altering cluster structures. Various stability criteria (e.g. binding energies, second differences in energy, and mixing energies) are used to evaluate the energetics, structures, and tendency of segregation in sub-nanometre Au–Pd clusters. HOMO–LUMO gaps were calculated to give additional information on cluster stability and a systematic homotop search was used to evaluate the energies of the generated global minima of mono-substituted clusters and the preferred doping sites, as well as confirming the validity of the BPGA-DFT approach.

A quantum Monte Carlo study of the structural and electronic properties of small cationic and neutral lithium clusters.

Using the fixed-node diffusion quantum Monte Carlo method, we calculate the total energy of small cationic and neutral lithium clusters. We estimate the ionization potential, atomic binding energy, dissociation energy, and the second difference in energy. We present a critical analysis of the structural and electronic properties of the clusters. The bond lengths and binding and dissociation energies obtained from the calculations are in excellent agreement with the available experimental results. A comparative analysis of the dissociation energy and the second difference in energy indicates that the cationic clusters Li3+, Li5+, and Li7+ are the most stable ones. We have also studied the electron correlation effects in the lithium clusters. The cationic clusters of odd-number size are relatively more favored in terms of correlation energy than their neighbors of even-number size. In the range of cluster sizes under investigation, we find that the contribution of electron correlation to ionization potential is not larger than 28% of its total values, whereas it enhances significantly the dissociation energy of the clusters reaching up to 70% of its total values for the most stable ones.

Theoretical study of the structures and chemical ordering of CoPd nanoalloys supported on MgO(001)

Metal nanoalloys on oxide surface are a widely studied topic in surface science and technology. In this study, the structures of CoPd nanoalloys adsorbed on MgO(001) have been searched by basin-hopping global optimization method within an atomistic model. Two different sizes (34 and 38 atom) have been considered for all compositions of CoPd/MgO(001) nanoalloys. Co and Pd atoms, for all the compositions, have cube-on-cube (001) epitaxy with substrate at interface. For both sizes, we have found that Pd rich composition nanoalloys have three layers, Co rich composition nanoalloys have four layers in morphology. Excess energy and second difference in energy analyzes have been performed to investigate the relative stability of nanoalloys with respect to their size and composition.

Quantum monte carlo study of the energetics of small hydrogenated and fluoride lithium clusters.

An investigation of the energetics of small lithium clusters doped either with a hydrogen or with a fluorine atom as a function of the number of lithium atoms using fixed-node diffusion quantum Monte Carlo (DMC) simulation is reported. It is found that the binding energy (BE) for the doped clusters increases in absolute values leading to a more stable system than for the pure ones in excellent agreement with available experimental measurements. The BE increases for pure, remains almost constant for hydrogenated, and decreases rapidly toward the bulk lithium for the fluoride as a function of the number of lithium atoms in the clusters. The BE, dissociation energy as well as the second difference in energy display a pronounced odd-even oscillation with the number of lithium atoms. The electron correlation inverts the odd-even oscillation pattern for the doped in comparison with the pure clusters and has an impact of 29%-83% to the BE being higher in the pure cluster followed by the hydrogenated and then by the fluoride. The dissociation energy and the second difference in energy indicate that the doped cluster Li3 H is the most stable whereas among the pure ones the more stable are Li2 , Li4 , and Li6 . The electron correlation energy is crucial for the stabilization of Li3 H. © 2016 Wiley Periodicals, Inc.

DFT global optimisation of gas-phase and MgO-supported sub-nanometre AuPd clusters.

The Birmingham Parallel Genetic Algorithm (BPGA) has been adopted for the global optimization of free and MgO(100)-supported Pd, Au and AuPd nanocluster structures, over the size range N = 4-10. Structures were evaluated directly using density functional theory, which has allowed the identification of Pd, Au and AuPd global minima. The energetics, structures, and tendency of segregation have been evaluated by different stability criteria such as binding energy, excess energy, second difference in energy, and adsorption energy. The ability of the approach in searching for putative global minimum has been assessed against a systematic homotop search method, which shows a high degree of success.

Activation of Pt–O and Pt–H bonds: DFT studies on adsorption of [Gd(H2O)n]3+ (n = 8–9) with Ptn (n = 3–7) cluster

In this work, “first-principles” Born–Oppenheimer Molecular Dynamics (BOMD) simulations were carried out for the solvation of Gd3+ with water to yield solvated [Gd (H2O)n]3+ (n=1–9) complexes, and the optimized structures were identified by frequency analysis. The second difference in energy (Δ2E) show that [Gd(H2O)8]3+ is more stable than the other complexes, exhibiting a peak associated with the first solvation shell. The second energy difference for [Gd(H2O)n–Ptm]3+ was also carried and it yields relative high stability for[Gd(H2O)8–Pt5]3+. The interaction of [Gd(H2O)n]3+ (n=8–9) with Ptn (n=3–7) clusters shows that [Gd (H2O)8]3+ adsorbs strongly on the Pt cluster by activating the Pt–H bond (2.55Å).

A density functional theory study of small bimetallic PtnAl (n=18) clusters

The geometries, stabilities and electronic properties of PtnAl (n=18) clusters are calculated using density functional theory at BPW91/LANL2DZ level. The stabilities of the ground states of PtnAl (n=18) clusters are discussed by means of the binding energy, the second difference in energy and energy gaps, and the magnetic properties. Mulliken charges are studied. The growth patterns for different sized PtnAl (n=18) clusters are of Al-substituted Ptn+1 clusters and they keep a similar framework of the most stable Ptn+1 clusters except Pt2Al. Al atoms in the ground state PtnAl isomer tend to occupy the most highly coordinated positions. The analyses of stabilities show that PtAl and Pt4Al are more stable than other clusters. Mulliken population analysis shows that charges are transferred from Al atoms to Pt atoms, which indicates that Al atom acts as electron donor in all PtnAl clusters. The analysis of magnetic property shows that doping an Al atom reduces the average atomic magnetic moment of the host Pd cluster. Pt-rich clusters which have a strong nonlinear optical effect and are easy to polarize by external electromagnetic field.