79 research outputs found
Piecewise linearity in the approximation for accurate quasiparticle energy predictions
We identify the deviation from the straight line error (DSLE) -- i.e., the
spurious non-linearity of the total energy as a function of fractional particle
number -- as the main source for the discrepancy between experimental vertical
ionization energies and theoretical quasiparticle energies, as obtained from
the and +SOSEX approximations to many-body perturbation theory (MBPT).
For self-consistent calculations, we show that suffers from a small DSLE.
Conversely, for perturbative and +SOSEX calculations the DSLE
depends on the starting point. We exploit this starting-point dependence to
reduce (or completely eliminate) the DSLE. We find that the agreement with
experiment increases as the DSLE reduces. DSLE-minimized schemes, thus, emerge
as promising avenues for future developments in MBPT
Measuring excitation-energy transfer with a real-time time-dependent density functional theory approach
We investigate the time an electronic excitation travels in a supermolecular
setup using a measurement process in an open quantum-system framework. The
approach is based on the stochastic Schr\"odinger equation and uses a
Hamiltonian from time-dependent density functional theory (TDDFT). It treats
electronic-structure properties and intermolecular coupling on the level of
TDDFT, while it opens a route to the description of dissipation and relaxation
via a bath operator that couples to the dipole moment of the density. Within
our study, we find that in supermolecular setups small deviations of the
electronic structure from the perfectly resonant case have only minor influence
on the pathways of excitation-energy transfer, thus lead to similar transfer
times. Yet, sizable defects cause notable slowdown of the energy spread
First steps towards achieving both ultranonlocality and a reliable description of electronic binding in a meta-generalized gradient approximation
It has been demonstrated that a meta-generalized gradient approximation (meta-GGA) to the exchange-correlation energy of density functional theory can show a pronounced derivative discontinuity and significant ultranonlocality similar to exact exchange, and can accurately predict the band gaps of many solids. We here investigate whether within the meta-GGA form these properties are compatible with a reasonable accuracy for electronic binding energies. With the help of two transparent and inexpensive correlation functional constructions we demonstrate that this is the case. We report atomization energies, show that reliable bond lengths are obtained for many systems, and find promising results for reaction barrier heights, while keeping the strong derivative discontinuity and ultranonlocality, and thus accuracy for band gaps
Magnetic moment quenching in small Pd clusters in solution
Small palladium clusters in vacuum show pronounced magnetic moments. With the help of Born–Oppenheimer molecular dynamics simulations based on density functional theory, we investigate for the paradigmatic examples of the Pd and the Pd cluster whether these magnetic moments prevail when the clusters are solvated. Our results show that the interaction with acetophenone quenches the magnetic moment. The reduction of the magnetic moment is a direct consequence of the electronic interaction between the Pd clusters and the solvent molecules, and not an indirect effect due to a different cluster geometry being stabilized by the solvation shell
Photoelectron spectra of anionic sodium clusters from time-dependent density-functional theory in real-time
We calculate the excitation energies of small neutral sodium clusters in the
framework of time-dependent density-functional theory. In the presented
calculations, we extract these energies from the power spectra of the dipole
and quadrupole signals that result from a real-time and real-space propagation.
For comparison with measured photoelectron spectra, we use the ionic
configurations of the corresponding single-charged anions. Our calculations
clearly improve on earlier results for photoelectron spectra obtained from
static Kohn-Sham eigenvalues
Simple iterative construction of the optimized effective potential for orbital functionals, including exact exchange
For exchange-correlation functionals that depend explicitly on the Kohn-Sham
orbitals, the potential V_{\mathrm{xc}\sigma}(\re) must be obtained as the
solution of the optimized effective potential (OEP) integral equation. This is
very demanding and has limited the use of orbital functionals like exact
exchange. We demonstrate that the OEP can be obtained iteratively by solving a
system of partial differential equations instead of an integral equation. This
amounts to calculating the orbital shifts that exactify the Krieger-Li-Iafrate
(KLI) approximation. Unoccupied orbitals do not need to be calculated. Accuracy
and efficiency of the method are shown for atoms and clusters using the exact
exchange energy. Counter-intuitive asymptotic limits of the exact OEP, not
accessible from previous constructions, are presented.Comment: Physical Review Letters, accepted for publication. 4 pages, 1 figur
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