Modeling liquid-liquid phase transitions and quasicrystal formation
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Abstract
In this thesis, studies which concern two different subjects related to phase transitions
in fluids and crystalline solids are presented. Condensed matter formation,
structure, and phase transitions are modeled using molecular dynamics simulations
of simple discontinuous potentials with attractive and repulsive interactions. Novel
phase diagrams are proposed for quasicrystals, crystals, and liquids.
In the first part of the thesis, the formation of a quasicrystal in a two dimensional
monodisperse system is investigated using molecular dynamics simulations of
hard sphere particles interacting via a two-dimensional square-well potential. It is
found that for certain values of the square-well parameters more than one stable
crystalline phase can form. By quenching the liquid phase at a very low temperature,
an amorphous phase is obtained. When this the amorphous phase is heated,
a quasicrystalline structure with five-fold symmetry forms. From estimations of the
Helmholtz potentials of the stable crystalline phases and of the quasicrystal, it is
concluded that within a specific temperature range, the observed quasicrystal phase
can be the stable phase.
The second part of the thesis concerns a study of the liquid-liquid phase transition
for a single-component system in three dimensions, interacting via an isotropic
potential with a repulsive soft-core shoulder at short distance and an attractive well
at an intermediate distance. The potential is similar to potentials used to describe [TRUNCATED}
Description
Thesis (Ph. D.)--Boston University, 2003.
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