Molecular dynamics simulations of spontaneous and seeded nucleation and theoretical calculations for zinc selenide

Abstract

Understanding and controlling the liquid to crystal transformation is a central topic for numerous natural phenomena and technological applications. However, the microscopic mechanism of crystal nucleation is still elusive, which leads to strong controversies regarding the ability of the most used model, the Classical Nucleation Theory (CNT), to describe nucleation rates in supercooled liquids. In this work, we were able to deeply supercool Zinc Selenide (ZnSe), and determine spontaneous homogeneous steady-state nucleation rates, JMD, by MD simulations using the mean lifetime method. At moderate supercoolings, where the nucleation rates are much smaller, we used the seeding method to compute the nucleation rates by the CNT formalism, JCNT, without any fitting parameter, using the physical properties obtained by MD simulations: the melting temperature, Tm, density, melting enthalpy, diffusion coefficient, D+, and the critical nucleus size, N∗, combined with two expressions for the thermodynamic driving force, Δμ. The values of interfacial free energy, γ, calculated by the CNT expression using the MD simulation data, via both the seeding method and the mean lifetime method at moderate and deep supercoolings show a weak temperature dependence, which is in line with the Diffuse Interface Theory. The extrapolated values of γ, from the spontaneous nucleation regime to the seeding nucleation region cover the range of values of γ calculated via the seeding method and the CNT formalism. Finally, the JCNT extrapolated from moderate supercoolings to deep supercoolings are in good agreement with the JMD. These results confirm the validity of the CNT.