13 research outputs found
Optical spectra of solids obtained by time-dependent density-functional theory with the jellium-with-gap model exchange-correlation kernel
Within the framework of ab initio time-dependent density-functional theory
(TD-DFT), we propose a static approximation to the exchange-correlation kernel
based on the jellium-with-gap model. This kernel accounts for electron-hole
interactions and it is able to address both strongly bound excitons and weak
excitonic effects. TD-DFT absorption spectra of several bulk materials (both
semiconductor and insulators) are reproduced in very good agreement with the
experiments and with a low computational cost.Comment: 5 pages, 3 figures, 1 tabl
Generalized Gradient Approximation Correlation Energy Functionals Based on the Uniform Electron Gas with Gap Model
We studied uniform electron gas with
a gap model in the context
of density functional theory. On the basis of this analysis, we constructed
two local gap models that are used in generalized gradient approximation
(GGA) correlation functionals that satisfy numerous exact constraints
for correlation energy. The first one, named GAPc, fulfills the full
second-order correlation gradient expansion at any density regime
and is very accurate for jellium surfaces, comparable to state-of-the-art
GGAs for atomic systems and molecular systems, and is well compatible
with known semilocal exchanges. The second functional, named GAPloc,
satisfies the same exact conditions, except that the second-order
gradient expansion is sacrificed for a better behavior under the Thomas–Fermi
scaling and a more realistic correlation energy density of the helium
atom. The GAPloc functional displays a high accuracy for atomic correlation
energies, still preserving a reasonable behavior for jellium surfaces.
Moreover, it shows a higher compatibility with the Hartree–Fock
exchange than other semilocal correlation functionals. This feature
is explained in terms of the real-space analysis of the GAPloc correlation
energy
Interfacial Electronic Structure of the Dipolar Vanadyl Naphthalocyanine on Au(111): “Push-Back” vs Dipolar Effects
We investigate the interfacial electronic structure of the dipolar organic semiconductor vanadyl naphthalocyanine on Au(111) in a combined computational and experimental approach to understand the role of the permanent molecular dipole moment on energy-level alignment at this interface. First-principles Density Functional Theory (DFT) calculations on such large systems are challenging, due to the large computational cost and the need to accurately consider dispersion interactions. Our DFT results with dispersion correction show a molecular deformation upon adsorption but no strong chemical bond formation. Ultraviolet photoelectron spectroscopy measurements show a considerable workfunction change of −0.73(2) eV upon growth of the first monolayer, which is well reproduced by the DFT calculations. This shift originates from a large electron density “push-back” effect at the gold surface, whereas the large out-of-plane vanadyl dipole moment plays only a minor role