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Uyen Tu Lieu

Publications and source records attributed to Uyen Tu Lieu.

4 recordsLinked to original sources

Dynamic control of self-assembly of quasicrystalline structures through reinforcement learning

We propose reinforcement learning to control the dynamical self-assembly of the dodecagonal quasicrystal (DDQC) from patchy particles. The patchy particles have anisotropic interactions with other particles and form DDQC. However, their structures at steady states are significantly influenced by the kinetic pathways of their structural formation. We estimate the best policy of temperature control trained by the Q-learning method and demonstrate that we can generate DDQC with few defects using the estimated policy. It is found that reinforcement learning autonomously discovers a characteristic temperature at which structural fluctuations enhance the chance of forming a globally stable state. The estimated policy guides the system toward the characteristic temperature to assist the formation of DDQC. We also illustrate the performance of RL when the target is metastable or unstable. To clarify the success of the learning, we analyse a simple model describing the kinetics of structural changes through the motion in a triple-well potential.

cond-mat.soft↗

Formation and Fluctuation of Two-dimensional Dodecagonal Quasicrystal

The self-assembly of two-dimensional dodecagonal quasicrystal (DDQC) from patchy particles are investigated by Brownian dynamics simulations. The patchy particle has a five-fold rotational symmetry pattern described by the spherical harmonics $Y_{55}$. From the formation of the DDQC obtained by an annealing process, we find the following mechanism. The early stage of the dynamics is dominated by hexagonal structures. Then, nucleation of dodecagonal motifs appears by particle rearrangement, and finally the motifs expand whole system. The transition from the hexagonal structure into the dodecagonal motif is made by the collective rational motion of the particles. The DDQC consists of clusters of dodecagonal motifs, which can be classified into several packing structures. By the analyses of the DDQC under fixed temperature, we find the fluctuations are characterised by changes in the network of the dodecagonal motifs. Finally we compare the DDQC assembled from the patchy particle system and isotropic particle system. The two systems both share a similar mechanism of the formation and fluctuation of DDQC.

cond-mat.soft↗

Inverse design of two-dimensional structure by self-assembly of patchy particles

We propose an optimisation method for the inverse structural design of self-assembly of anisotropic patchy particles. The anisotropic interaction can be expressed by the spherical harmonics of the surface pattern on a patchy particle, and thus arbitrary symmetry of the patch can be treated. The pairwise interaction potential includes several to-be-optimised parameters, which are the coefficient of each term in the spherical harmonics. We use the optimisation method based on the relative entropy approach and generate structures by Brownian Dynamics simulations. Our method successfully estimates the parameters in the potential for the target structures, such as square lattice, kagome lattice, and dodecagonal quasicrystal.

cond-mat.soft↗

Topological defects of dipole patchy particles on a spherical surface

We investigate the assembly of the dipole-like patchy particles confined to a spherical surface by Brownian dynamics simulations. The surface property of the spherical particle is described by the spherical harmonic $Y_{10}$, and the orientation of the particle is defined as the uniaxial axis. On a flat space, we observe a defect-free square lattice with nematic order. On a spherical surface, defects appear due to the topological constraint. As for the director field, four defects of winding number $+1/2$ are observed, satisfying the Euler characteristic. We have found many configurations of the four defects lying near a great circle. Regarding the positional order for the square lattice, eight grain boundary scars proliferate linearly with the sphere size. The positions and orientations of the eight grain boundary scars are strongly related to the four $+1/2$ defect cores.

cond-mat.soft↗