Structural properties of amorphous aluminum and aluminum-nitrogen alloys. Computer simulations
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Structural properties of amorphous aluminum and aluminum-nitrogen alloys. Computer simulations Ariel A. Valladares* Instituto de Investigaciones en Materiales, UNAM, Apartado Postal 70-360, México, D. F. 04510, MEXICO Alexander Valladares, R. M. Valladares and A. Calles Departamento de Física, Facultad de Ciencias, UNAM, Apartado Postal 70-542, México, D. F. 04510, MEXICO _____________________________________________________________________________ Abstract Liquid and amorphous metallic systems have proven difficult to model. Some efforts have relied on the use of parameterized classical potentials of the Lennard-Jones type or geometric hard sphere simulations, but first principles approaches have been rarely used. Clearly a knowledge of atomic structures is paramount for calculating physical properties. In this work we apply our recently developed ab initio DFT approach (A. A. Valladares et al., Eur. Phys. J. 22 (2001) 443) for the generation of amorphous semiconducting materials, to amorphize aluminum and an aluminum-nitrogen alloy. We report radial distribution functions (RDFs) and specific atomic structures of periodic amorphous/liquid cubic supercells of 108 atoms with a volume of (12.1485 Å)3, generated using the Harris functional. Keywords: Amorphous metallic systems; Liquid metallic systems; a-AlN; l-AlN; metallic glasses, Radial Distribution Functions _____________________________________________________________________________
1. Antecedents We recently developed a new approach for the generation of amorphous semiconducting structures that has led to very good results in the simulational studies of these technologically important materials [1]. Now we want to explore the applicability of these techniques to the study of metallic glasses. Liquid and amorphous metallic systems have proven difficult to model and the simulacional study of their structures is an ongoing task where the application of first principles methods has been largely overlooked. Most of the approaches used for metals are along the lines of classical molecular dynamics using Lennard-Jones type interatomic potentials and classical pseudopotentials [2], and the ideal hard-sphere dense random-packing model [3].
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Contacting author. E-mail: [email protected]
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Concepts like the fundamental structure-forming principle of high packing efficiency, random packing, and quasi-crystallinity are frequently invoked in the study of metals [4, 5]. A densitymatrix approach reports that the electronic structure of liquid aluminum is similar to a nearlyfree-electron-like behavior [6], a result intuitively appealing. However, we have found no simulations of liquid or amorphous aluminum using an ab initio approach. Amorphous aluminum-nitrogen was studied to compare it with recent results obtained by our group for SiN, which are in very good agreement with experiment [7], and for C-N [8].
Experimental studies of amorphous pure aluminum are non-existent or very difficult to obtain [9] and this makes comparisons practically impos
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