AlH3andAl2H6: Magic Clusters with Unmagical Properties (original) (raw)
Related papers
Molecular Orbital Interpretation of Magic Clusters with Non-Magic Numbers
Chemphyschem, 2009
Clusters with some particular numbers of valence electrons (VEs) show enhanced stability against dissociation. These clusters, termed "magic" clusters, could act as candidates for novel cluster-assembled materials. The spherical jellium model predicts that clusters with 2, 8, 20, 40, … VEs have higher stability due to the closure of electronic shells. A popular example is the magic I h Al 13 À cluster, which has 40 valence electrons, constituting a filled-shell configuration (1s) 2 (1p) 6 (1d) 10 (2s) 2 (1f) 6 (2p) 6 - Each electron shell is characterized by a radial quantum number N and an angular quantum number L. The valence electrons of the constituent atoms in simple pure metal clusters can be considered as itinerant. However, it is not clear if this behaviour can be extrapolated to heterogeneous clusters composed of two metals. The geometric and electronic properties of a binary metal cluster are different from those of a simple metal cluster because the valence electrons, atomic radii, and electronegativities of the two elements are different. Even for binary metal clusters, it is common that the more stable clusters correspond to systems where the total number of VEs equals one of the known spherical magic numbers. However, this is not the case for all stable binary clusters. Herein, we examine Al 12 Cs À (38 VEs) and Al 11 Cs 2
Al(He)3+N Clusters:A Theoretical Study
Current Science
The geometries and electronic structure of molecular ions containing helium (He) atoms complexed to sodium (Na), magnesium (Mg) and aluminium (Al) cations have been studied computationally using density functional and wavefunction-based methods. The complexation of He atoms depends on the charge on the metal centre. While complexation with Na + and Mg 2+ is very weak, that with Al 3+ is found to be strong. The highest coordination number (N) for AlHe 3 N + is found to be 11, which is a true minimum in the potential energy surface. Topological analysis within the realm of quantum theory of atoms in molecules reveals closed-shell interaction in these systems.
Structural and electronic properties of an [(Al2O3)4]+ cluster
Journal of Molecular Modeling, 2015
Density functional theory (DFT) has been applied to investigate the structural and electronic properties of an [(Al 2 O 3 ) 4 ] + cluster. Since there is no structural data available from experiment, the geometry of the cluster was obtained based on a model which produced the best agreement with vibrational IR-MPD data. A range of different exchangecorrelation functionals were tested, and it was concluded that the best spectral agreement was produced using the CAM-B3LYP and B3LYP functionals, respectively. To further characterize the properties of the cluster, natural bond order analysis was performed, and it was concluded that an appropriate description for the system is [Al 8 O 12 ] + . The frontier orbitals and spin densities of both cation and neutral systems were considered, and it was concluded that the unrestricted singlet and triplet spin densities of the neutral [Al 8 O 12 ] system were nearly degenerate, representing a di-radical, with the triplet state being lower in energy.
Structural and electronic properties of aluminum-based binary clusters
Physical review, 2001
We investigate the low-energy geometries and the electronic structure of several aluminum based clusters, viz. Al 4 X 4 , (XϭLi, Na, K, Be, Mg, B, and Si͒ by first principle Born-Oppenheimer molecular dynamics within the framework of density-functional theory. We present a systematic analysis of the bonding properties and discuss the validity of spherical jellium model. We find that the structure of eigenstates for clusters with metallic elements conform to the spherical jellium model. The 20 valence electron systems Al 4 Be 4 and Al 4 Mg 4 exhibit a large highest-occupied-lowest-unoccupied ͑HOMO-LUMO͒ gap due to shell closing effect. In clusters containing alkali-metal atom, Al 4 behaves as a superatom that is ionically bonded to them. The Al-Al bond in both Al 4 Si 4 and Al 4 B 4 clusters is found to be covalent.
The Journal of Chemical Physics, 2010
We have studied the interaction of CH 4 with Al 2 and Al 3 neutral and charged clusters in the two lowest lying spin states using density functional theory. These calculations, via extended search, are used to determine the stable positions of H and CH 3 near the cluster, and the transition state to break the H -CH 3 bond. In all cases, stable methyl-aluminum-hydrides are possible. The H desorption is studied by means of vibration analysis and application of transition state theory. A common observed trend is that, in breaking the H -CH 3 bond, the interacting H atom is attached to the "surface" of the clusters attracting some negative charge of Ϸ0.2e. The charge transfer is illustrated using the corresponding orbitals near the transition state in conjunction with the computed Mulliken population analysis. Thermal vibrations, generally, do not enhance the reaction. In all exothermic cases, the binding energy toward CH 3 + HAl n charge increases with increasing charge of the original Al n ͑q=−1,0,1͒ cluster. Although Al lacks occupied d-orbitals, the small Al clusters reduce the ͑free methane͒ CH 3 -H dissociation barrier except for Al 3 ͑q=−1,0͒ . The relevant reactions in desorption require ϳ400-700°C.
Journal of Chemical Physics, 2019
The Diffusion Monte Carlo (DMC) method was applied to anionic hydrogen clusters H − (H 2 ) n (n = 1–16, 32) and their deuterated analogs using a polarizable all-atom potential energy surface (PES) developed by Calvo and Yurtsever. For the hydrogen clusters, the binding energy ∆E n appears to be a smooth function of the cluster size n, thus contradicting the previous claim that n = 12 is a “magic number” cluster. The structures of the low energy minima of the PES for these clusters belong to the icosahedral motif with the H 2 molecules aligned toward the central H − ion. However, their ground state wavefunctions are highly delocalized and resemble neither the structures of the global nor local minima. Moreover, the strong nuclear quantum effects result in a nearly complete orientational disordering of the H 2 molecules. For the deuterium clusters, the ground state wavefunctions are localized and the D 2 molecules are aligned toward the central D − ion. However, their structures are still characterized as disordered and, as such, do not display size sensitivity. In addition, DMC simulations were performed on the mixed H − (H 2 ) n (D 2 ) p clusters with (n, p) = (6, 6) and (16, 16). Again, in contradiction to the previous claim, we found that the “more quantum” H 2 molecules prefer to reside farther from the central H − ion than the D 2 molecules.
Journal of Physical Chemistry C, 2018
Results of photoelectron spectroscopy measurements and density functional theory complemented with correction scheme calculations on electron binding energy (EBE) spectra of anionic Al n Mo, n = 3−5 and 7, clusters are presented and analyzed. The analysis points to the important role of dynamical fluxionality and multiplicity of structural forms as contributing factors in the measured spectra. Using the example of Al 4 Mo − as a paradigmatic case, the separate roles of size, structure/symmetry, and composition in evolving the EBE spectra of precursor pure clusters (in this case, Al 4 − and Al 5 −) into those of bimetallic clusters are demonstrated utilizing a new methodology we developed recently (
The Journal of Physical Chemistry A, 2002
Structure and bonding in Al 3 O n and Al 3 O naluminum oxide clusters where n ) 1-3 are studied with electronic structure calculations and are compared with some experimental results. Geometry optimizations with the B3LYP/6-311+G(2d,p) density functional method produced minima which were verified with frequency calculations. Several initial geometries and distinct spin multiplicities were considered for each case. The most stable anionic structures from density functional calculations were confirmed with additional geometry optimizations at the QCISD level. Equilibrium geometries, harmonic frequencies, and atomic charges are presented. These results, in combination with previous assignments of anion photoelectron spectra, provide a consistent explanation for changes in isomerization energies between anionic and neutral species.
A theoretical investigation on the clusters by density functional theory methods
2005
The first systematic study of the CrðH 2 OÞ 0;1C n ðnZ 1K4Þ series of clusters is herein presented at the level of the unrestricted DFT B3LYP level in conjunction with electron core potential basis sets. The present structures are relevant for laser-induced and laser-ablation syntheses of chromium compounds, and also for fundamental spectroscopy studies of metal-bearing species in the gas phase. Calculated properties include optimal geometries, total energies, bond lengths, bond angles, natural orbital analysis charges, hydration dissociation energies, and HOMO-LUMO gaps inter alia. Present results reveal a strict correlation between the clusters total energy and their spin state. Except for CrðH 2 OÞ 0C 4 , the most stable clusters in each CrðH 2 OÞ 0;1C n ðnZ 1-4Þ series are high-spin states. Comparisons with a few available theoretical results show good agreement. q Journal of Molecular Structure: THEOCHEM 756 (2005) 55-61 www.elsevier.com/locate/theochem 0166-1280/$ -see front matter q
Theoretical study of structure and stability of h+x (h2)n clusters
Chemical Physics Letters, 1981
Structural parameters, energies, and spectroscopic characteristics of two series of layerwise hydrogenated aluminum clusters Al 44 H n (n = 27-44) and Al 89 H т (т = 15, 24, 39, and 63) have been calculated by the density functional theory method. It has been shown that increasing number of H atoms in both series entails rapid enhancement of structural distortions up to cooperative rearrangements accompanied by a change in the shape and composition of the surface layer and internal core of the cluster. At the end of the first series Al 44 H n , several surface atoms migrate to the outer sphere of the cage to form valence-unsaturated "outer-surface" AlH n and Al 2 H n moieties, which can be active sites at the stages of deeper hydrogenation. Simultaneously, the inner core [Al] 5 disintegrates, and its atoms are introduced into the surface layer. A family of "inverted" Al 42 H 42 isomers with the hollow [Al 42 ] cage has been localized; the isomers contain the endohedral AlH 4 group and "inner" Al−H bonds with their hydrogen end directed to the center of the inner cavity. At the end of the second series, five alanate groups AlH 4 and two Al 3 H 2 fragments bonded to the surface through hydrogen bridges are formed in the outer sphere of the cluster. The results are of interest for DFT modeling of hydrogenation of nanosized aluminum clusters at the molecular level.