Electronic structure of aluminum arsenide nanocrystals Using Ab initio large unit cell method


The ab initio restricted Hartree-Fock method is used to simulate the electronic structure of aluminum arsenide nanocrystals consists of (216-738 atoms) with sizes ranging up to about 2.5 nm in diameter. The calculations are divided into two parts, surface and core. The oxygenated (001)-(1×1) facet that expands with larger sizes of nanocrystals is investigated to determine the rule of the surface in nanocrystals electronic structure. Results show that lattice constant and ionicity of the core part are decreasing by increasing the size of nanocrystals. The smallest investigated nanocrystal is 1.83% larger in lattice constant and 13.5% larger in ionicity than the converged value of largest investigated nanocrystal. Increasing nanocrystals size also resulted in an increase of core cohesive energy (absolute value), increase of core energy gap, and increase of the core valence bandwidth. The surface states are found mostly non-degenerated because of the effect of surface discontinuity and oxygen atoms. The method shows fluctuations in the converged energy gap, valence bandwidth and cohesive energy of core part of nanocrystals duo to shape variation. The present work suggests the addition of ionicity and lattice constant to the quantities that are affected by quantum confinement phenomenon. The method of the present model has threefold results; it can be used to approach the electronic structure of crystals bulk, surface, and nanocrystals.