Title: Equilibrium configurations of large nanostructures using the embedded saturated-fragments stochastic density functional theory,
Abstract: An \emph{ab initio} Langevin dynamics approach is developed based on
stochastic density functional theory (sDFT) within a new \emph{embedded
saturated } \emph{fragment }formalism, applicable to covalently bonded systems.
The forces on the nuclei generated by sDFT contain a random component natural
to Langevin dynamics and its standard deviation is used to estimate the
friction term on each atom by satisfying the fluctuation\textendash dissipation
relation. The overall approach scales linearly with system size even if the
density matrix is not local and is thus applicable to ordered as well as
disordered extended systems. We implement the approach for a series of silicon
nanocrystals (NCs) of varying size with a diameter of up to $3$nm corresponding
to $N_{e}=3000$ electrons and generate a set of configurations that are
distributed canonically at a fixed temperature, ranging from cryogenic to room
temperature. We also analyze the structure properties of the NCs and discuss
the reconstruction of the surface geometry.