  The in-plane coefficient of thermal expansion (CTE) for CdSe nanoplatelets
with the zinc-blende structure containing from two to five monolayers is
calculated from first principles within the quasiharmonic approximation. A
comparison of the obtained results with those for bulk CdSe with both the
zinc-blende and wurtzite structures finds a significant increase in the
magnitude of negative CTE and the temperature range of its observation in
nanoplatelets. The main contribution to the negative thermal expansion in CdSe
nanoplatelets is given by the out-of-plane flexural ZA mode and in-plane
optical $E$ modes that arise from the folding of TA phonon of bulk CdSe.
