79 research outputs found
An improved exchange-correlation potential for polarizability and dissociation in DFT
We propose a novel approach to the problem of polarizabilities and
dissociation in electric fields from the static limit of the Vignale-Kohn (VK)
functional. We consider the response to the purely scalar part of the VK
response potential.This potential has ground-state properties that notably
improve over the full VK response density and over usual (semi-)local
functionals. The correct qualitative behavior of our potentials means that it
is expected to work well for polarizabilities in cases such as the H chain,
and it will also correctly dissociate open-shell fragments in a field.Comment: 4 pages, 3 figures; to appear in JC
The Exact Potential Driving the Electron Dynamics in Enhanced Ionization
It was recently shown that the exact factorization of the electron-nuclear
wavefunction allows the construction of a Schr\"odinger equation for the
electronic system, in which the potential contains exactly the effect of
coupling to the nuclear degrees of freedom and any external fields. Here we
study the exact potential acting on the electron in charge-resonance enhanced
ionization in a model one-dimensional H molecule. We show there can be
significant differences between the exact potential and that used in the
traditional quasistatic analyses, arising from non-adiabatic coupling to the
nuclear system, and that these are crucial to include for accurate simulations
of time-resolved ionization dynamics and predictions of the ionization yield
Long-range excitations in time-dependent density functional theory
Adiabatic time-dependent density functional theory fails for excitations of a
heteroatomic molecule composed of two open-shell fragments at large separation.
Strong frequency-dependence of the exchange-correlation kernel is necessary for
both local and charge-transfer excitations. The root of this is static
correlation created by the step in the exact Kohn-Sham ground-state potential
between the two fragments. An approximate non-empirical kernel is derived for
excited molecular dissociation curves at large separation. Our result is also
relevant for the usual local and semi-local approximations for the ground-state
potential, as static correlation there arises from the coalescence of the
highest occupied and lowest unoccupied orbital energies as the molecule
dissociates.Comment: 7 pages, 2 figure
- …