Time-domain non-adiabatic ab initio simulations are performed to study the phonon-assisted hot electron relaxation dynamics in CdSe QD, EQD and LQD, which are of the same diameter but an increasing length along c axis. Our work shows that both the length and system temperature have a strong impact on the electronic properties and electron relaxation dynamics of the CdSe QRs. Higher frequency phonons are excited and scattered with electrons at higher temperatures. The band gap shows a negative dependence on the temperature. The band gap decreases and the electron and hole density of states increase with increasing the length. However, not all the properties studied here vary with the length in a straight way. The band gap shows a stronger negative temperature dependence for the EQD than the QD and LQD. The electron-phonon couples stronger in the EQD than the QD and LQD. The hot electron relaxation proceeds faster in the EQD than the QD and LQD. Furthermore, the hot electron decay rate varies linearly with the average electron density of states and this linear relationship can be well described by the Fermi’s golden rule and of practical use in predicting the hot electron decay rate with the knowledge of the average NA coupling and electron density of states.

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