  We study the energetics of quasi-particle excitations in CsPbBr3 perovskite
nanocrystals using path integral molecular dynamics simulations. Employing
detailed molecular models, we elucidate the interplay of anharmonic lattice
degrees of freedom, dielectric confinement, and electronic correlation on
exciton and biexciton binding energies over a range of nanocrystal sizes. We
find generally good agreement with some experimental observations on binding
energies, and additionally explain the observed size dependent Stokes shift.
The explicit model calculations are compared to simplified approximations to
rationalize the lattice contributions to binding. We find that polaron
formation significantly reduces exciton binding energies, whereas these effects
are negligible for biexciton interactions. While experimentally, the binding
energy of biexcitons is uncertain, based on our study we conclude that
biexcitons are bound in CsPbBr3.
