Large nuclear zero-point motion effect in semiconductor nanoclusters

We show, using an ab initio approach, that the quantum zero-point atomic motion has strong effects on the electronic properties of carbon and silicon nanoclusters. The ensuing band-gap renormalization is between 0.3 and 0.9 eV and is as large as the corresponding exciton binding energy. These results call for a critical reassessment of the quality of nanocluster calculations performed assuming frozen atom positions, even in the zero-temperature limit. Our approach allows to separate the effect into different spatial contributions (surface, core, passivants) and to quantify on which electronic states (according to their symmetries) the effect is strongest.