3 research outputs found
KineticNet: Deep learning a transferable kinetic energy functional for orbital-free density functional theory
Orbital-free density functional theory (OF-DFT) holds the promise to compute
ground state molecular properties at minimal cost. However, it has been held
back by our inability to compute the kinetic energy as a functional of the
electron density only. We here set out to learn the kinetic energy functional
from ground truth provided by the more expensive Kohn-Sham density functional
theory. Such learning is confronted with two key challenges: Giving the model
sufficient expressivity and spatial context while limiting the memory footprint
to afford computations on a GPU; and creating a sufficiently broad distribution
of training data to enable iterative density optimization even when starting
from a poor initial guess. In response, we introduce KineticNet, an equivariant
deep neural network architecture based on point convolutions adapted to the
prediction of quantities on molecular quadrature grids. Important contributions
include convolution filters with sufficient spatial resolution in the vicinity
of the nuclear cusp, an atom-centric sparse but expressive architecture that
relays information across multiple bond lengths; and a new strategy to generate
varied training data by finding ground state densities in the face of
perturbations by a random external potential. KineticNet achieves, for the
first time, chemical accuracy of the learned functionals across input densities
and geometries of tiny molecules. For two electron systems, we additionally
demonstrate OF-DFT density optimization with chemical accuracy.Comment: 10 pages, 8 figure
Tuning UV Pump X‑ray Probe Spectroscopy on the Nitrogen K Edge Reveals the Radiationless Relaxation of Pyrazine: <i>Ab Initio</i> Simulations Using the Quasiclassical Doorway–Window Approximation
Transient absorption UV pump X-ray probe spectroscopy
has been
established as a versatile technique for the exploration of ultrafast
photoinduced dynamics in valence-excited states. In this work,
an ab initio theoretical framework for the simulation
of time-resolved UV pump X-ray probe spectra is presented. The method
is based on the description of the radiation–matter interaction
in the classical doorway–window approximation and a surface-hopping
algorithm for the nonadiabatic nuclear excited-state dynamics. Using
the second-order algebraic–diagrammatic construction scheme
for excited states, UV pump X-ray probe signals were simulated for
the carbon and nitrogen K edges of pyrazine, assuming a duration of
5 fs of the UV pump and X-ray probe pulses. It is predicted that spectra
measured at the nitrogen K edge carry much richer information about
the ultrafast nonadiabatic dynamics in the valence-excited states
of pyrazine than those measured at the carbon K edge
Influence of Core Substitution on the Electronic Structure of Benzobisthiadiazoles
Benzobisthiadiazoles (BBTs) are promising organic semiconductors
for applications in field effect transistors and solar cells since
they possess a strong electron-accepting characteristic. Thereby,
the electronic structure of organic/metal interfaces and within thin
films is essential for the performance of organic electronic devices.
Here, we study the structural and electronic properties of two BBTs,
with different core substitution patterns, a phenyl (BBT-Ph) and a
thiophene (BBT-Th) derivative adsorbed on Au(111) using vibrational
and electronic high-resolution electron energy loss spectroscopy in
combination with state-of-the-art quantum chemical calculations. In
the mono- and multilayer, both BBTs adopt a planar adsorption geometry
with the molecular backbone, as well as the phenyl and thiophene side
groups are oriented parallel to the gold substrate. The energies of
the lowest excited electronic singlet states (S) and the first triplet
state (T1) are determined. The optical gap (S0 → S1 transition) is found to be 2.2 eV for BBT-Ph
and 1.6 eV for BBT-Th. The energy of T1 is identified to
be 1.2 eV in BBT-Ph and in the case of BBT-Th 0.7 eV. Thus, both the
optical gap size as well as the T1 energy are drastically
reduced in BBT-Th compared to BBT-Ph. Based on our quantum chemical
calculations, this is attributed to the electron-rich nature of the
five-membered thiophene rings in conjunction with their preference
for planar geometries. Variation of the substitution pattern in BBTs
opens an opportunity for tailoring their electronic properties