2 research outputs found
Accelerating Realtime TDDFT with Block-Orthogonalized Manby–Miller Embedding Theory
Realtime
time-dependent density-functional theory (RT-TDDFT) is
one of the most practical techniques available to simulate electronic
dynamics of molecules and materials. Promising applications of RT-TDDFT
to study nonlinear spectra and energy transport demand simulations
of large solvated systems over long time scales, which are computationally
quite costly. In this paper, we apply an embedding technique developed
for ground-state SCF methods by Manby and Miller to accelerate realtime
TDDFT. We assess the accuracy and speed of these approximations by
studying the absorption spectra of solvated and covalently split chromophores.
Our embedding approach is also compared with less accurate, less costly
QM/MM charge embeddings. We find that by mixing levels of detail the
embedded mean-field theory scheme is a simple, accurate, and effective
way to accelerate RT-TDDFT simulations
Origin of the Size-Dependent Stokes Shift in CsPbBr<sub>3</sub> Perovskite Nanocrystals
The
origin of the size-dependent Stokes shift in CsPbBr<sub>3</sub> nanocrystals
(NCs) is explained for the first time. Stokes shifts
range from 82 to 20 meV for NCs with effective edge lengths varying
from ∼4 to 13 nm. We show that the Stokes shift is intrinsic
to the NC electronic structure and does not arise from extrinsic effects
such as residual ensemble size distributions, impurities, or solvent-related
effects. The origin of the Stokes shift is elucidated via first-principles
calculations. Corresponding theoretical modeling of the CsPbBr<sub>3</sub> NC density of states and band structure reveals the existence
of an intrinsic confined hole state 260 to 70 meV above the valence
band edge state for NCs with edge lengths from ∼2 to 5 nm.
A size-dependent Stokes shift is therefore predicted and is in quantitative
agreement with the experimental data. Comparison between bulk and
NC calculations shows that the confined hole state is exclusive to
NCs. At a broader level, the distinction between absorbing and emitting
states in CsPbBr<sub>3</sub> is likely a general feature of other
halide perovskite NCs and can be tuned via NC size to enhance applications
involving these materials