Binding and Diffusion of Al Adatoms and Dimers on the Si(100)-2 × 1 Reconstructed Surface: A Hybrid QM/MM Embedded Cluster Study (original) (raw)
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Journal of Physical Chemistry C, 2009
When group III metals are deposited onto the Si(100)-2 × 1 reconstructed surface they are observed to selfassemble into chains of atoms that are one atom high by one atom wide. To better understand this onedimensional island growth, ab initio electronic structure calculations on the structures of Al atoms on silicon clusters have been performed. Natural orbital occupation numbers show that these systems display significant diradical character, suggesting that a multireference method is needed. A multiconfiguration self-consistent field (MCSCF) calculation with a 6-31G(d) basis set and effective core potentials was used to optimize geometries. The surface integrated molecular orbital molecular mechanics embedded cluster method was used to take the surface chemistry into account, as well as the structure of an extended surface region. Potential energy surfaces for binding of Al adatoms and Al−Al dimers on the surface were determined, and the former was used to obtain a preliminary assessment of the surface diffusion of adatoms. Hessians were calculated to characterize stationary points, and improved treatment of dynamic electron correlation was accomplished using multireference second order perturbation theory (MRMP2) single-point energy calculations. Results from the MRMP2//MCSCF embedded cluster calculations are compared with those from QM-only cluster calculations, embedded cluster unrestricted density functional theory calculations, and previous Car−Parrinello DFT studies.
Chem Phys, 1995
The binding energies and configurations for single Si adatoms on the Si͑100͒ surface are investigated theoretically. Detailed comparisons between previously published and new calculations using classical potentials, semiempirical formulations, and density functional theory ͑DFT͒ are made. The DFT calculations used both the plane-wave-pseudopotential approach in a periodic slab geometry and the Gaussian-orbital based all-electron approach employing cluster geometries. In the local-density approximation excellent agreement between the cluster and slab results was obtained. Inclusion of gradient corrections to the exchange-correlation energy significantly improves absolute binding energies and changes relative energies by as much as 0.3-0.5 eV depending on the particular exchange-correlation functional used. Binding energies and relative energies obtained using the classical potentials disagree with the gradient corrected DFT energies at about the 0.6-0.9 eV level, and most find qualitatively different local minima from those found in the DFT calculations. The semiempirical approaches give results intermediate in quality between those of the classical potentials and the ab initio calculations. Analysis of the energies and binding site geometries provides insight into the shortcomings of some of the classical potentials.
International Journal of Nanotechnology, 2010
We report an extensive first-principles investigation of the structure and electronic properties of small Si n (n = 1, 2, 3, 4, and 6) clusters deposited on the Au(111) surface. The calculations were performed using a plane wave based pseudopotential method under the framework of density functional theory. The electron-ion interaction energy has been described using ultrasoft pseudopotentials (USPP) and the spin polarised GGA scheme was used for the exchange correlation energy. The results reveal that Si atom prefers to adsorb on the hcp site of the Au(111) surface with strong binding energy. For Si 3 , the closed triangle geometry of the bare cluster forms an open triangle by rupturing one of the three Si-Si bonds. Remarkable structural changes in the gas phase geometries were observed from Si 4 onwards. For example, while the adsorption of rhombus in parallel and perpendicular orientation to the surface plane remains almost unaltered, the tetrahedral conformation becomes almost flat by the interaction of Au surface. The nature of chemical
The Journal of Chemical Physics, 1995
The binding energies and configurations for single Si adatoms on the Si͑100͒ surface are investigated theoretically. Detailed comparisons between previously published and new calculations using classical potentials, semiempirical formulations, and density functional theory ͑DFT͒ are made. The DFT calculations used both the plane-wave-pseudopotential approach in a periodic slab geometry and the Gaussian-orbital based all-electron approach employing cluster geometries. In the local-density approximation excellent agreement between the cluster and slab results was obtained. Inclusion of gradient corrections to the exchange-correlation energy significantly improves absolute binding energies and changes relative energies by as much as 0.3-0.5 eV depending on the particular exchange-correlation functional used. Binding energies and relative energies obtained using the classical potentials disagree with the gradient corrected DFT energies at about the 0.6 -0.9 eV level, and most find qualitatively different local minima from those found in the DFT calculations. The semiempirical approaches give results intermediate in quality between those of the classical potentials and the ab initio calculations. Analysis of the energies and binding site geometries provides insight into the shortcomings of some of the classical potentials.
Surface Science, 2004
Icosahedral 55, 147 and 309 Al clusters were studied by means of tight binding zero temperature calculations and molecular dynamics simulations. We focus on the properties of the free and also of the deposited clusters on the low indexed Al surfaces. We found that the free Al clusters have lower melting temperatures and bulk moduli than the bulk material, while they exhibit enhanced low and high-energy phonon density of states. This behaviour is related mainly to the size of the clusters, while when deposited on the low index Al surfaces although they preserve their compactness, they reconstruct rapidly adopting the substrate's structure. In addition, the supported clusters do not alter significantly the surface vibrational behaviour, while when combining between them they recover a bulk like behaviour. In addition, the calculated electronic density of states revealed significant enhancement at energies around the Fermi level that was found to be due to charge transfer from the inner atoms towards the surface atoms.
The European Physical Journal B, 2012
We report a first-principle investigation of the structure and electronic properties of small Sin (n = 1−6, 9) clusters deposited on the Au(111) and Ag surfaces. The calculations were performed using a plane wave based pseudopotential method under the framework of density functional theory. The results reveal the preference of Si atom to be adsorbed on the h.c.p. site of the metal (111) surfaces with strong binding energy. We study monolayer (ML) deposition as well as the cluster deposition on both the surfaces. The clusters introduce interlayer forces in the adsorbate. Based on PDOS (projected density of states) analysis it is found that Si atoms acquire charges from the Au/Ag surface. The binding energies are consistent with the known cohesive energy of Ag and Au silicides. The planar Sin cluster deposition on metal surfaces show that Au provides an adjustable surface with relatively strong Au-Si interaction while Ag-Si relatively weak interaction leading to dimerization of Si. The strong bonding with the surface atoms is a result of p-d hybridization. Some of the 3-D clusters show shape distortions after deposition on metal surfaces. This leads to internal stresses after deposition. A statistical parameter is defined over PDOS. It helps to measure the state delocalization in energy. Implications of the Si-Metal interaction on the initial stages of growth are discussed.
1997
Differently sized cluster calculations are used to investigate theoretically the preferred adsorption site for an AI adatom on the Si(lll) surface. By performing partial geometry optimizations at the Hartree Fock level on A1Si, subclusters around the site of interest we find significant A1 adatom-induced surface relaxation effects distorting the Si atoms from their bulk lattice positions. The largest relaxation effects take place at the T 4 site resulting in AI adsorption at the T4 site to be 5 kcal/mol more stable than at the H 3 site and considerably more stable than adsorption at the T~ site. However, we only have confidence in this result after performing for the T4 site a partial geometry optimization on the AISi 5 subcluster in the AISiz6H24 cluster and by including appropriate correlation corrections. ~') 1997 Elsevier Science B.V.
2008
We present fully ab-initio calculations of van der Waals coefficients for two different situations: i) the interaction between hydrogenated silicon clusters; and ii) the interactions between these nanostructures and a non metallic surface (a silicon or a silicon carbide surface). The methods used are very efficient, and allow the calculation of systems containing hundreds of atoms. The results obtained are further analyzed and understood with the help of simple models. These models can be of interest for molecular dynamics simulations of silicon nanostructures on surfaces, where they can give a very fast yet sufficiently accurate determination of the van der Waals interaction at large separations.
Surface Science, 2006
Density functional theory (DFT) calculations have been used to characterize the bonding geometry in Si nanostructures, such as trimers (Si 3 ), tetramers (Si 4 ) and hexamers (Si 6 ) formed on a Si(1 1 1) surface. Trimers and tetramers were simulated by placing three respectively four Si adatoms in high symmetry adsorption sites on the Si(1 1 1) surface. For Si 6 clusters, a combination of these adsorption sites were used. We found that only trimer and tetramer formed by adsorbing Si adatoms in ontop position can be considered as clusters because of bonding interaction among their constituents. For hexamers, bonds are also formed between Si adatoms suggesting their existence as stable entity.