  The lifetime of non-equilibrium electrons and holes in semiconductors is
crucial for solar cell and optoelectronic applications. Non-adiabatic molecular
dynamics (NAMD) simulations based on time-dependent density functional theory
(TDDFT) are widely used to study excited-state carrier dynamics. However, the
calculated carrier lifetimes are often different from experimental results by
orders of magnitude. In this work, by revisiting the definition of carrier
lifetime and considering different recombination mechanisms, we report a
systematic procedure for calculating the effective carrier lifetime in
realistic semiconductor crystals that can be compared directly to experimental
measurements. The procedure shows that considering all recombination mechanisms
and using reasonable densities of carriers and defects are crucial in
calculating the effective lifetime. When NAMD simulations consider only
Shockey-Read-Hall (SRH) defect-assisted and band-to-band non-radiative
recombination while neglect band-to-band radiative recombination, and the
densities of non-equilibrium carriers and defects in supercell simulations are
much higher than those in realistic semiconductors under solar illumination,
the calculated lifetimes are ineffective and thus differ from experiments.
Using our procedure, the calculated effective lifetime of the halide perovskite
CH3NH3PbI3 agrees with experiments. It is mainly determined by band-to-band
radiative and defect-assisted non-radiative recombination, while band-to-band
non-radiative recombination is negligible. These results indicate that it is
possible to calculate carrier lifetimes accurately based on NAMD simulations,
but the directly calculated values should be converted to effective lifetimes
for comparison to experiments. The revised procedure can be widely applied in
future carrier lifetime simulations.
