6 research outputs found
Applicability of the CaldeiraâLeggett Model to Vibrational Spectroscopy in Solution
Formulating a rigorous systemâbath
partitioning approach
remains an open issue. In this context, the famous CaldeiraâLeggett
model that enables quantum and classical treatment of Brownian motion
on equal footing has enjoyed popularity. Although this model is by
any means a useful theoretical tool, its ability to describe anharmonic
dynamics of real systems is often taken for granted. In this Letter,
we show that the mapping between a molecular system under study and
the model cannot be established in a self-consistent way, unless the
system part of the potential is taken effectively harmonic. Mathematically,
this implies that the mapping is not invertible. This âinvertibility
problemâ is not dependent on the peculiarities of particular
molecular systems and is rooted in the anharmonicity of the system
part of the CaldeiraâLeggett model potential
Tuning Range-Separated Density Functional Theory for Photocatalytic Water Splitting Systems
We discuss the system-specific optimization
of long-range-separated
density functional theory (DFT) for the prediction of electronic properties
relevant for a photocatalytic cycle based on an IrÂ(III) photosensitizer
(IrPS). Special attention is paid to the charge-transfer properties,
which are of key importance for the photoexcitation dynamics but cannot
be correctly described by means of conventional DFT. The optimization
of the range-separation parameter using the ÎSCF method is discussed
for IrPS including its derivatives and complexes with electron donors
and acceptors used in photocatalytic hydrogen production. Particular
attention is paid to the problems arising for a description of medium
effects by means of a polarizable continuum model
Nuclear Dynamical Correlation Effects in Xâray Spectroscopy from a Theoretical Time-Domain Perspective
To
date X-ray spectroscopy has become a routine tool that can reveal
highly local and element-specific information on the electronic structure
of atoms in complex environments. Here, we focus on nuclear dynamical
correlation effects in X-ray spectra and develop a rigorous time-correlation
function method employing ground state classical molecular dynamics
simulations. The importance of nuclear correlation phenomena is demonstrated
by comparison against the results from the conventional sampling approach
performed on the same data set for gas phase water. In contrast to
the first-order absorption, second-order resonant inelastic scattering
spectra exhibit pronounced fingerprints of nuclear motions. The developed
methodology is not biased to a particular electronic structure method
and, owing to its generality, can be applied to, e.g., X-ray photoelectron
and Auger spectroscopies
Origin of the Two Bands in the B800 Ring and Their Involvement in the Energy Transfer Network of <i>Allochromatium vinosum</i>
Bacterial
photosynthesis features robust and adaptable energy-harvesting
processes in which light-harvesting proteins play a crucial role.
The peripheral light-harvesting complex of the purple bacterium <i>Allochromatium vinosum</i> is particularly distinct, featuring
a double peak structure in its B800 absorption band. Two hypothesesî¸not
necessarily mutually exclusiveî¸concerning the origin of this
splitting have been proposed; either two distinct B800 bacteriochlorophyll
site energies are involved, or an excitonic dimerization of bacteriochlorophylls
within the B800 ring takes place. Through the use of two-dimensional
electronic spectroscopy, we present unambiguous evidence that excitonic
interaction shapes the split band. We further identify and characterize
all of the energy transfer pathways within this complex by using a
global kinetic fitting procedure. Our approach demonstrates how the
combination of two-dimensional spectral resolution and self-consistent
fitting allows for extraction of information on light-harvesting processes,
which would otherwise be inaccessible due to signal congestion
Electron- and Energy-Transfer Processes in a Photocatalytic System Based on an Ir(III)-Photosensitizer and an Iron Catalyst
The
reaction pathways of bis-(2-phenylpyridinato-)Â(2,2â˛-bipyridine)ÂiridiumÂ(III)Âhexafluorophosphate
[IrÂ(ppy)<sub>2</sub>(bpy)]ÂPF<sub>6</sub> within a photocatalytic water
reduction system for hydrogen generation based on an iron-catalyst
were investigated by employing time-resolved photoluminescence spectroscopy
and time-dependent density functional theory. Electron transfer (ET)
from the sacrificial reagent to the photoexcited Ir complex has a
surprisingly low probability of 0.4% per collision. Hence, this step
limits the efficiency of the overall system. The calculations show
that ET takes place only for specific encounter geometries. At the
same time, the presence of the iron-catalyst represents an energy
loss channel due to a tripletâtriplet energy transfer of Dexter
type. This loss channel is kept small by the employed concentration
ratios, thus favoring the reductive ET necessary for the water reduction.
The elucidated reaction mechanisms underline the further need to improve
the sun lightâs energy pathway to the catalyst to increase
the efficiency of the photocatalytic system
Chemical Bonding in Aqueous Ferrocyanide: Experimental and Theoretical Xâray Spectroscopic Study
Resonant inelastic X-ray scattering
(RIXS) and X-ray absorption
(XA) experiments at the iron L- and nitrogen K-edge are combined with
high-level first-principles restricted active space self-consistent
field (RASSCF) calculations for a systematic investigation of the
nature of the chemical bond in potassium ferrocyanide in aqueous solution.
The atom- and site-specific RIXS excitations allow for direct observation
of ligand-to-metal (Fe L-edge) and metal-to-ligand (N K-edge) charge-transfer
bands and thereby evidence for strong Ď-donation and Ď-backdonation.
The effects are identified by comparing experimental and simulated
spectra related to both the unoccupied and occupied molecular orbitals
in solution