A blended NPT/NVT scheme for simulating metallic glasses

作者：Hamilton Nicholas E^*; Mahjoub Reza; Laws Kevin J; Ferry Michael

来源：Computational Materials Science, 2017, 130: 130-137.

DOI：10.1016/j.commatsci.2017.01.006

• Ab initio molecular dynamics
• Zirconium based metallic glasses
• Simulation methods
• Canonical ensemble
• Isobaric-isothermal ensemble

We present details of a blended quantum molecular dynamics scheme, utilizing both the canonical and isobaric-isothermal ensembles, in order to not only circumvent the need for any experimental input data ordinarily required for simulations involving the strictly canonical ensemble, but also minimize the relatively high extra computational cost imposed by the increased cutoff energy necessary to avoid the so called Pulay stress error while performing isobaric-isothermal ab initio molecular dynamics simulations using plane-wave basis set. We compare the results of the blended and canonical schemes via the simulated quench of the damage-tolerant Zr61Ti2Cu25Al12 (ZT1) alloy to below its glass transition temperature. There were subtle differences in structural evolution between the two schemes. Notably, the blended scheme generates a more efficiently packed structure, which is feasibly permitted due to the volume changes that transpire as a result of incorporating a parallel NPT component. Further, while the blended scheme obviates the need for any experimental input data, it is shown that the starting volume is not particularly critical and the computed final density of the alloy is within 1% of the reported experimental value of 6.43-6.50 g/cm(3). Furthermore, the blended scheme demonstrated a greater degree of transformation in the coordination number compared with the canonical, which remains relatively static. The final value of 12.97 obtained from the blended scheme is closer to the ideal of 13.33 as per close packing theory, a feature that appears to be related to the evolution of a more complex family of Voronoi polyhedra relative to the icosahedral dominant motifs present in the canonical scheme. Furthermore, in both schemes, the partial coordination number in the Zr species, being the primary constituent, demonstrates a plateau in its evolution, but which commences in the blended scheme at a temperature approximately 300 K closer to the reported glass transition temperature. The findings suggest a more reliable and an Optimally efficient method for implementing ab initio molecular dynamics in the simulation of complex alloys.

• 出版日期2017-4-1