The programmed crystallization of particles into lowsymmetry lattices represents a major synthetic challenge in the field of colloidal crystal engineering. Herein, we report an approach to realizing such structures that relies on a library of low-symmetry Au nanoparticles, with synthetically adjustable dimensions and tunable aspect ratios. When modified with DNA ligands and used as building blocks for colloidal crystal engineering, these structures enable one to expand the types of accessible lattices and to answer mechanistic questions about phase transitions that break crystal symmetry. Indeed, crystals formed from a library of elongated rhombic dodecahedra yield a rich phase space, including low-symmetry lattices (body-centered tetragonal and hexagonal planar). Molecular dynamics simulations corroborate and provide insight into the origin of these phase transitions. In particular, we identify an unexpected asymmetry in the DNA shell, distinct from both the particle and lattice symmetries, which enables directional, nonclose-packed interactions.

Sublattice melting is the loss of order of one lattice component in binary or ternary ionic crystals upon increasing the temperature. A related transition has been predicted in colloidal crystals. To understand the nature of this transition, we study delocalization in self-assembled, size-asymmetric binary colloidal crystals using a generalized molecular dynamics model. Focusing on body-centered cubic (BCC) lattices, we observe a smooth change from localized-to-delocalized interstitial particles for a variety of interaction strengths. Thermodynamic arguments, mainly the absence of a discontinuity in the heat capacity, suggest that the passage from localization-to-delocalization is continuous and not a phase transition. This change is enhanced by lattice vibrations, and the temperature of the onset of delocalization can be tuned by the strength of the interaction between the colloid species. Therefore, the localized and delocalized regimes of the sublattice are dominated by enthalpic and entropic driving forces, respectively. This work sets the stage for future studies of sublattice melting in colloidal systems with different stoichiometries and lattice types and it provides insights into superionic materials, which have the potential for application in energy storage technologies.

High-performance materials rely on small reorganization energies to facilitate both charge separation and charge transport. Here, we performed DFT calculations to predict small reorganization energies of rectangular silicene nanoclusters with hydrogen-passivated edges denoted by H-SiNC. We observe that across all geometries, H-SiNCs feature large electron

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Utilizing density functional theory (DFT) and a complete active space self-consistent field (CASSCF) approach,we study the electronic properties of rectangular silicene nano clusters with hydrogen passivated edges denoted by H-SiNCs (n,n), with n and n representing the zigzag and armchair directions, respectively. The results show that in the n direction, the H-SiNCs prefer to be in a singlet (S = 0) ground state for n > n. However, a transition from a singlet (S = 0) to a triplet (S = 1) ground state is revealed for n > n. Through the calculated Raman spectrum, the S = 0 and S = 1 ground states can be observed by the E (G) and A (D) Raman modes. Furthermore, H-SiNC clusters are shown to have HOMO-LUMO (HL) energy gaps, which decrease as a function of n and n for S = 0 and S = 1 states. The H-SiNC with a S = 1 ground state can be potentially used for silicene-based spintronic devices.

Colloidal crystals formed by size-asymmetric binary particles co-assemble into a wide variety of colloidal compounds with lattices akin to ionic crystals. Recently, a transition from a compound phase with a sublattice of small particles to a metal-like phase in which the small particles are delocalized has been predicted computationally and observed experimentally. In this colloidal metallic phase, the small particles roam the crystal maintaining the integrity of the lattice of large particles, as electrons do in metals. A similar transition also occurs in superionic crystals, termed sublattice melting. Here, we use energetic principles and a generalized molecular dynamics (MD) model of a binary system of functionalized nanoparticles (NPs) to analyze the transition to sublattice delocalization in different co-assembled crystal phases as a function of temperature (T ), number of grafted chains on the small particles, and number ratio between the small and large particles n s :n l . We find that n s :n l is the primary determinant of crystal type due to energetic interactions and interstitial site filling, while the number of grafted chains per small particle determines the stability of these crystals. We observe first-order sublattice delocalization transitions as T increases, in which the host lattice transforms from low-to high-symmetry crystal structures, including A20 → BCT → BCC, A d → BCT → BCC, and BCC → BCC/FCC → FCC transitions and lattices. Analogous sublattice transitions driven primarily by lattice vibrations have been seen in some atomic materials exhibiting an insulator-metal transition also referred to as metallization. We also find minima in the lattice vibrations and diffusion coefficient of small particles as a function of n s :n l , indicating enhanced stability of certain crystal structures for n s :n l values that form compounds. I. INTRODUCTIONBinary colloids of size-asymmetric particles have been shown to co-assemble into a diverse set of binary crystals [1][2][3][4][5][6][7][8]. These crystals are compounds akin to atomic ionic crystals because the smaller particles occupy interstitial sites of a lattice formed by the large particles.Recently the exploration of binary colloidal crystals with highly size-asymmetric functionalized NPs has yielded the observation of crystal assemblies where the small NPs delocalize, rather than remaining fixed at interstitial sublattice sites [9][10][11].

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