Atomistic Modeling of Transformations in Ionic Semiconductor Nanocrystals

Prashant Jain, University of Illinois at Urbana-Champaign

Usage Details

Impurity doping of semiconductor nanocrystals is often utilized for making new functional nanoscale electronic and optical materials as well as superionic solids and battery electrodes. Cation exchange is a method that is becoming popular for such doping of nanocrystals. However, control of the final composition and structure of the nanocrystalline phase resulting from doping requires mechanistic understanding of the process. Therefore, we study the atomistic mechanism of a model cation exchange reaction using plane-wave density functional theory (DFT). In particular, we are determining the relaxed geometries, energies, and band structures for cadmium selenide (CdSe) nanocrystals at varying levels of doping. With these calculations, we will be able to determine the energetics and mechanism in the doping of CdSe by a range of ions such as Cu⁺, Ag⁺, and Hg²⁺. We have found both from literature studies and our own preliminary investigations that hybrid functionals are necessary to accurately describe how a crystal lattice relaxes about an impurity atom and/or an associated atomic vacancy—a phenomenon that we expect contributes significantly to the reaction mechanism. Blue Waters would play a crucial role in our research by making hybrid functional structural relaxations feasibly expeditious. These relaxations are composed of multiple hybrid functional scf calculations, each of which can consume numerous days of calculation time on few cores without GPU acceleration. Thus, without access to Blue Waters, the potential time scale of hybrid functional relaxations and their cost in node-hours severely limits the scope and number of computational investigations we can pursue.