Structure, stability, dipole polarizability and differential polarizability in small gallium arsenide clusters from all-electron ab initio and density-functional-theory calculations (original) (raw)
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The Journal of Chemical Physics, 2007
We report reliable ab initio finite field ͑hyper͒polarizability values at Hartree-Fock and second order Møller-Plesset perturbation theory ͑MP2͒ levels of theory for different geometrical configurations of small gallium arsenide clusters Ga n As n with n =2-5. We relied on all-electron basis sets and pseudopotentials suitable for ͑hyper͒polarizability calculations. In each case, we used structures that have been established in the literature after we optimized their geometries at B3LYP/cc-pVTZ-PP level of theory. Our results suggest that the first order hyperpolarizability ͑͒ is much more sensitive to the special geometric features than the second order hyperpolarizability ͑␥͒. For the most stable configurations up to ten atoms the second order hyperpolarizability at MP2 level of theory varies between 15ϫ 10 4 and 32ϫ 10 4 e 4 a 0 4 E h −3 . In addition, we examined the polarizability per atom evolution versus the cluster size for Ga n As n with n =2-9. Our work extends earlier theoretical studies which were limited to eight atoms and exposes that the polarizability/atom of the most stable stoichiometric configurations up to Ga 9 As 9 continues the monotonic downward trend with increasing size. Lastly, from the methodological point of view, our analysis shows that apart from polarizabilities, augmented pseudopotentials yield reliable first and second hyperpolarizability values as well.
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.
Physical Review A, 2009
A systematic investigation of the structures and the dependence of the dipole polarizabilities on the composition of closed and open shell gallium arsenic clusters is presented. Our investigation focuses on nine gallium arsenide ͑GaAs͒ clusters with five and six total number of atoms of systematically varying composition. These clusters are the smallest species of small GaAs clusters which have attracted substantial attention due to their strongly oscillating experimental polarizability values. The ground states of those clusters have been determined using a global approach which combines molecular dynamics and an automatic procedure of comparing and selecting cluster structures based on pattern recognition techniques. The polarizabilities have been studied by means of coupled cluster techniques complemented by a semi-empirical hybrid functional which includes corrections from perturbation theory. Our global structural investigation found two different structures for Ga 4 As 2 and Ga 1 As 5 which are lower in energy than the previously reported ones. The performed polarizability investigation suggests that open shell GaAs systems composed of five atoms are not more polarizable than closed-shell clusters built by six atoms as is indirectly implied by the reported experimental data. Also, the polarizabilities of those species increase as a function of the number of Ga in a monotonic but not systematic manner. The observed increase type is explained by the large atomic polarizabilities of Ga and in terms of the particular structural and bonding features of a given cluster. Furthermore, the comparison between our theoretical values and earlier experimental polarizability estimations clearly shows that for the five-atomic clusters, the reported experimental polarizability is not largely overestimated as was previously believed. Our results for the six-atomic cluster demonstrate that the polarizability per atom of a six atomic GaAs cluster of any composition is larger than the polarizability of the bulk material, contrary to what has been demonstrated by the experiment.
Computational study of GanAsm (m + n = 2–9) clusters using DFT calculations
Journal of Nanoparticle Research, 2019
Gallium arsenide is a semiconductor compound with well-known properties in its bulk phase. Theoretical works explain some of the properties of this material at a cluster scale; nevertheless, more research is required to fully understand these systems. In this work, we used the density functional theory (DFT) formalism, specifically the PBE functional and the TZ2P basis set for the study of structural, electronic, and chemical properties of Ga n As m (m + n = 2-9) clusters in the gas phase, for all possible compositions. Our study reveals that the structural and electronic properties in Ga n As m clusters present a size and composition dependence, with a size range within 3-10 Å. Even/odd behavior is observed in most electronic and chemical properties of the clusters. The even/odd behavior is related to the electronic close shell structure of the system. It is found that the predominance of arsenic atoms in the Ga n As m clusters generate comparatively more stable molecules, with lower binding energies per atom, higher hardness values, ionization potentials, and Gap HOMO-LUMO .
Structures and polarizabilities of medium-sized Ga n As m clusters
Density functional theory calculations on medium-sized Ga n As m clusters (n + m = 17-24, n À m = 0, ±1) are reported. The total polarizabilities of Ga n As m clusters exhibit a linear dependence on their volumes despite of different composition, giving a way to predict the polarizabilities of larger clusters. The polarizabilities are also strongly correlated to ionization potentials and composition. Isomerization may be the main reason why the even-odd oscillation of polarizabilities disappears in this size from experiment. Ultra stability of Ga 9 As 10 and unusual electronic properties of Ga 10 As 11 are found due to their special structures.
Structural Chemistry, 2013
The structural and electronic properties of the neutral gallium sulfide (GaS 2 , Ga 2 S 2 , GaS 4 , and Ga 2 S 4) clusters along with their anionic counterparts have been investigated systematically using the density functional theory, the second-order Møller-Plesset perturbation theory (MP2), and coupled cluster singles and doubles, including noniterative triples [CCSD(T)] with the 6-311?G(2df) basis set. At the CCSDT(T)//MP2 level, the lowest-energy configurations of the gallium sulfides prefer to be cyclic (GaS 2), linear (GaS 2-), kite shape with a thiozonide unit (GaS 4 and GaS 4-), rhombic (Ga 2 S 2 and Ga 2 S 2-), and planar with two sulfur atoms in a terminal position (Ga 2 S 4 and Ga 2 S 4-) geometries. In the gallium-sulfur binary clusters considered in this study, the neutral and anionic ground-state geometries prefer the planar structures with alternation of gallium and sulfur atoms. All the neutral clusters, with the exception of Ga 2 S 2 , possess high electron affinities, which range from 3.51 to 3.64 eV at the CCSDT(T)//MP2 level. A sequential addition of a sulfur atom to the Ga 2 S n (n = 1-3) system increases the charge transfer from gallium atoms to sulfur atoms, the adiabatic electron affinity, and the HOMO-LUMO gap. The sufficiently large HOMO-LUMO gaps ensure the stability of these gallium sulfide clusters. The Ga 2 S 4 ? Ga 2 S 2 ? S 2 process is the most thermodynamically favored toward dissociation.
Journal of Physical Chemistry A, 2007
Low-lying equilibrium geometric structures of Al n N (n ϭ 1-12) clusters obtained by an all-electron linear combination of atomic orbital approach, within spinpolarized 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 Al 7 N cluster to be endowed with special stability.
Theoretical Study of Neutral and Ionic States of Small Clusters of Ga
The structure, bonding, vibrational, and electronic properties of small clusters of gallium oxide, Ga m O n (m, n) 1, 2) are studied here with a focus on the changes induced by the addition or removal of an electron from the neutral species. It is found that the addition of an electron introduces relatively larger structural changes than the removal of an electron from the neutral cluster. The values of ionization potential and electron affinity of these clusters are calculated, for the first time, in this study. Analysis of the atomic charges and electronic properties predicts a kind of instability in Ga 2 O-. In Ga 2 O 2 , the linear Ga-O-Ga-O isomer forms the ground state of the neutral cluster. The cationic structure also prefers the linear configuration, since the ionized electron comes out of an antibonding molecular orbitals of the neutral Ga 2 O 2. The anionic Ga 2 O 2 , on the other hand, prefers the rhombus structure as a ground state since LUMO of the neutral Ga 2 O 2 consists of a Ga-O bonding orbital.
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.