Reactions and Interfacial Behaviors of the Water–Amorphous Silica System from Classical and Ab Initio Molecular Dynamics Simulations Page: 38
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2.3 Classical Molecular Dynamics (MD)
Classical MD is one of the most commonly implemented atomistic simulation
methods to investigate the changing properties of materials with time, pressure,
temperature and composition. They were first performed by Alder and Wainwright in the
late 1950s to simulate the force between two hard spheres [208,209]. Since then,
improvements in both the algorithms and the tools used to perform calculations have
occurred. With current computational efficiency, MD simulations can be performed with
as many as a tens of millions of atoms [210] for microseconds. This is far beyond what
can be done using more accurate electronic structure methods such as DFT. The
efficiency of classical MD methods relies on the use of forcefields to describe
interatomic interactions, rather than calculating the forces from the electronic structure
of the individual atoms. Each atom is then treated as one unit, without differentiating
between electrons and the nuclei. Therefore, the accuracy of the results are heavily
dependent on the development and parameterization of a forcefield, and each atomic
interaction needs to be explicitly included in the potential. Forcefields are often fitted
with a mixture of experimental and ab initio data depending on what is available. For
instance, experiments can provide macroscopic properties (density, mechanical
properties) for a variety of crystal polymorphs while highly accurate DFT methods can
provide bond distance and bond angle information.
The development of classical MD potentials for glassy structures can be
complicated by its non-equilibrium nature, and that perhaps using crystalline
polymorphs for fitting amorphous potential parameters will result in unrealistic structures
in the model. Previous studies have found that, even if a forcefield is fitted almost38
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Rimsza, Jessica M. Reactions and Interfacial Behaviors of the Water–Amorphous Silica System from Classical and Ab Initio Molecular Dynamics Simulations, dissertation, May 2016; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc849660/m1/49/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .