Computational study of GanAsm (m + n = 2–9) clusters using DFT calculations (original) (raw)
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Physical Review A, 2008
We have employed conventional ab initio and density-functional-theory ͑DFT͒ methods to study the structure, stability and electric polarizability of small gallium arsenide clusters Ga n As n . We relied on purposeoriented, carefully optimized basis sets of Gaussian-type functions. We have calculated both the mean dipole polarizability ͑␣ ͒ and the anisotropy ͑⌬␣͒. Our results show that the differential-per-atom polarizability of the most stable isomers decreases rapidly with cluster size. Compared to the ab initio results, the widely used Becke's three-parameter exchange DFT functional with the Lee, Yang, and Parr correlation functional and Becke's three-parameter exchange DFT functional with Perdew and Wang's 1991 gradient-corrected correlation functional density-functional-theory methods follow clearly the trend of the differential-per-atom polarizability ␣ diff / atom for the most stable isomers and predict values closer to the self-consistent field method but distinctly lower than second-order Møller-Plesset perturbation theory. All methods predict a positive value for the dimer, ␣ diff / atom ͑Ga 2 As 2 ͒ Ͼ 0.
Journal of Structural Chemistry, 2018
Various structural possibilities for small gallium-indium Ga m In n-m (n = 4, 6, 8 and m < n) clusters are investigated using the density functional theory (DFT) method at the B3LYP/TZP level. The optimized structures tend to prefer compact structures, wherein the trigonal prism and rhombic prism configurations are favoured for n = 6 and 8, respectively. The bonding energy per atom is calculated according to the cluster size. The HOMO-LUMO gaps, ionization potentials, electron affinities, and chemical hardness (η) are also computed for the most stable isomers of each cluster and used to predict their relative stabilities. The obtained results indicate that the Ga-rich clusters are more stable than the In-rich ones with the same total number of atoms. The Ga-Ga bond is stronger than the GaIn bond and the latter is stronger than the In-In one. Therefore, the Ga 7 In cluster is relatively the most stable structure. The relative reactivity of Ga m In n-m (n = 4, 6, 8 and m < n) clusters could be predicted based on the chemical hardness. The computed large HOMO-LUMO gap energies could be used as an index of the kinetic stability for the studied clusters.
Molecular cluster model of the electronic structure of substitutional impurities in gallium arsenide
Chemistry of Materials, 1989
The embedded cluster LCAO-SCC method, within the DV-Xa local density formalism, has been used to investigate the electronic structure of the cation vacancy and of the substitutional Cu impurity in GaAs. The host gap has been found to be 0.8 eV. The pure GaAs and the point defects were represented by GaAs4Ga12, V*As4Ga12 (V* = vacancy), and CuAslGa12 tetrahedral embedded clusters, respectively. The main features of perturbations induced into the host bonding scheme by point defects are thoroughly discussed. Present calculations predict a Cu acceptor state 30 meV above the valence-band edge, in close agreement with experiments. (1) (a) Universita di Potenza: (b) CNR of Padova: (c) Universite di Padova.
The Journal of Physical Chemistry B, 2000
First principles calculations based on the nonlocal density approximation to the density functional theory were performed to study structures, stabilities, and vibrational properties of small (monomer, triatomic, and dimer) neutral and ionized clusters of AlN, GaN, and InN. As a general trend, triatomic isomers prefer doublet spin states, whereas triplets are predicted for the monomer and the linear dimer clusters. Both nitrogenexcess and metal-excess triatomic clusters show minimum energy configurations to be approximately linear. The most stable isomer of Al 2 N 2 and Ga 2 N 2 is a rhombus with a singlet spin state, though In 2 N 2 is predicted not to be stable against dissociation into In 2 and N 2 . A strong dominance of the N-N bond over the metalnitrogen and metal-metal bonds appears to control the structural skeletons and the chemistry of these clusters. This is manifested in the dissociation of neutral and singly-ionized clusters, where the loss of metal atoms is shown to be the most likely fragmentation channel, except in the case of the dimer, in which the formation of two homonuclear diatomics is favored. The vibrational modes and frequencies are also explained in terms of the different bond strengths found in the diatomic clusters.
Journal of Molecular Modeling, 2012
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.
Computational and Theoretical Chemistry, 2014
Density functional calculations using Wu and Cohen generalized gradient approximation functional are performed to investigate the structural properties and relative stability of silver doped gold clusters AgAu nÀ1 (n = 3-13). Low-lying energy structures include two dimensional and three dimensional geometries. Especially, for the lowest energy structures, the transition from planar to three dimensional structures is found to occur at n = 13 and the impurity Ag atom prefers to occupy higher coordination sites. The calculated binding energies, second-order differences in energies, dissociation energies and HOMO-LUMO energy gaps show pronounced odd-even oscillating behaviors, indicating that clusters with even number of atoms keep a higher relative stability than their neighboring odd-numbered ones. Particularly, the cluster AgAu 5 shows the strongest stability. Moreover, vertical ionization potential, vertical electronic affinity, and chemical hardness are discussed and compared in depth. The same odd-even oscillations are found.
Structure and Polarizability of Small (GaAs)n Clusters (n= 2, 3, 4, 5, 6, and 8)
Computing Letters, 2006
We studied the structure and polarizability of small stoichiometric gallium arsenide clusters (GaAs) n (n= 2, 3, 4, 5, 6 and 8) with conventional ab-initio and density functional methods relying on correlation consistent large-core relativistic pseudo potential basis set. Our results show that computations based on those basis sets yield reasonable results compared to all electron basis sets and the polarizability/atom of small gallium arsenide clusters up to the octamer, is predicted to be larger than the Clausius-Mosotti bulk value.
Journal of Materials Science, 2012
A study of the Ga 2 Te 3 and Ga 3 Te 2 clusters is presented using three different levels of theory, namely; DFT, MP2 and CCSD(T). We used the 6-311G(d) basis set for gallium atom and the LANL2DZdp ECP basis set for tellurium atom. The results include geometrical parameters, vibrational frequencies and energies of the low-lying structures. We report the vertical electron detachment energy (VEDE) and adiabatic electron detachment energy (AEDE) for the anionic species. The neutral Ga 2 Te 3 cluster adopts a V-shape configuration with 1 A 1 ground state whilst its anion is kite shaped with 2 A 1 ground state. On the other hand, the Ga 3 Te 2 and Ga 3 Te 2¯s pecies prefer a three dimensional 6-D 3h geometry with 2 A 2 00 and 1 A 1 0 electronic states, respectively. The adiabatic electron affinity (AEA) for Ga 2 Te 3 is 2.78 eV and that of Ga 3 Te 2 is 2.86 eV at the CCSD(T)//B3LYP level. We analyse, discuss and compare the findings of our research with the analogous gallium chalcogenides.
1995
Significant advances have been made recently toward understanding the properties of materials through theoretical approaches. These approaches are based either on first-principles quantum mechanical formulations or semiempirical formulations, and have benefitted from increases in computational power. The advent of parallel computing has propelled the theoretical approaches to a new level of realism in modelling physical systems of interest. The theoretical methods and simulation techniques that are currently under development are bound to become powerful tools in understanding, exploring and predicting the properties of existing and novel materials.
This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHI-AIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure , total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is −114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].