In this work we review our new methods to computer generate amorphous atomic topologies of several binary alloys: SiH, SiN, CN; binary systems based on group IV elements like SiC; the GeSe2 chalcogenide; aluminum-based systems: AlN and AlSi, and the CuZr amorphous alloy. We use an ab initio approach based on density functionals and computationally thermally-randomized periodically-continued cells with at least 108 atoms. The computational thermal process to generate the amorphous alloys is the undermelt-quench approach, or one of its variants, that consists in linearly heating the samples to just below their melting (or liquidus) temperatures, and then linearly cooling them afterwards. These processes are carried out from initial crystalline conditions using short and long time steps. We find that a step four-times the default time step is adequate for most of the simulations. Radial distribution functions (partial and total) are calculated and compared whenever possible with experimental results, and the agreement is very good. For some materials we report studies of the effect of the topological disorder on their electronic and vibrational densities of states and on their optical properties.
Much attention has been given to bulk metallic glasses (BMG) in recent years, particularly those based on binary alloys due to the simplicity of their atomic composition. Although efforts to understand the atomistic features that give rise to their exceptional properties have been made, the electronic and vibrational properties have been disregarded. We undertook the task of simulating the Cu 64 Zr 36 glassy metal using a supercell with 108 atoms and a different simulational approach: the undermelt-quench approach [1]. The structure was characterized by means of the radial (pair) distribution function and the bond-angle distribution and the electronic density of states was calculated. We find that our results agree well with experimental data.
We report ab initio-based processes to generate an amorphous nanoporous Cu64Zr36 metallic glass. Starting with two different initial configurations: an unstable crystalline sample (cCu64Zr36) and an amorphous sample (aCu64Zr36), the transferable expanding lattice methodpreviously used with semiconducting and pure metal systems-was applied in order to increase the volume of the cells (and atomic distances proportionally) so that the density was halved, thus obtaining 50% porosity. The initial samples were subjected to either constant room temperature ab initio molecular dynamics or geometry optimization only, which resulted in well-defined pores growing along specific spatial directions. Herewith we report partial and total pair distribution functions, as well as nearest neighbor distances and coordination numbers which let us discern differences in backbone and pore topology. Also we report the bond-angle distribution which let us track the presence of icosahedral-like short-range order which is often related to the glass forming ability in amorphous alloys. The so-called depletion of the pair distribution function at mid range order reported in the literature, along with an estimation of pore sizes are also reported.
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