Abstract: | In this article, we discuss the stability of soft quasicrystalline phases in a
coupled-mode Swift-Hohenberg model for three-component systems, where the characteristic
length scales are governed by the positive-definite gradient terms. Classic
two-mode approximation method and direct numerical minimization are applied to
the model. In the latter approach, we apply the projection method to deal with the potentially
quasiperiodic ground states. A variable cell method of optimizing the shape
and size of higher-dimensional periodic cell is developed to minimize the free energy
with respect to the order parameters. Based on the developed numerical methods,
we rediscover decagonal and dodecagonal quasicrystalline phases, and find diverse
periodic phases and complex modulated phases. Furthermore, phase diagrams are
obtained in various phase spaces by comparing the free energies of different candidate
structures. It does show not only the important roles of system parameters, but also
the effect of optimizing computational domain. In particular, the optimization of computational
cell allows us to capture the ground states and phase behavior with higher
fidelity. We also make some discussions on our results and show the potential of applying
our numerical methods to a larger class of mean-field free energy functionals. |