Comprehensive Ab Initio Study of Electronic, Optical, and Cohesive Properties of Silicon Quantum Dots of Various Morphologies and Sizes up to Infinity

We present a comprehensive and integrated model-independent ab initio study of the structural, cohesive, electronic, and optical properties of silicon quantum dots of various morphologies and sizes in the framework of all-electron "static" and time-dependent density functional theory (DFT, TDFT), using the well-tested B3LYP and other properly chosen functional(s). Our raw ab initio results for all these properties for hydrogen-passivated nanocrystals of various growth models and sizes from 1 to 32 Å are subsequently fitted, using power-law dependence with judicially selected exponents, based on dimensional and other plausibility arguments. As a result, we can not only reproduce with excellent accuracy known experimental and well-tested theoretical results in the regions of overlap but also extrapolate successfully all the way to infinity, reproducing the band gap of crystalline silicon with almost chemical accuracy as well as the cohesive energy of the infinite crystal with very good accuracy. Thus, our results could be safely used, among others, as interpolation and extrapolation formulas not only for cohesive energy and band gap but also for interrelated properties, such as dielectric constant and index of refraction of silicon nanocrystals of various sizes all the way up to infinity.