1,002 research outputs found
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
Continuum states from time-dependent density functional theory
Linear response time-dependent density functional theory is used to study
low-lying electronic continuum states of targets that can bind an extra
electron. Exact formulas to extract scattering amplitudes from the
susceptibility are derived in one dimension. A single-pole approximation for
scattering phase shifts in three dimensions is shown to be more accurate than
static exchange for singlet electron-He scattering.Comment: 5 pages, 2 figures, J. Chem. Phys. accepte
Magnetic properties of doped GdI2
Motivated by the recent experimental studies on layered ferromagnetic
metallic system GdI2 and its doped variant GdI2Hx we develop a model to
understand their ground state magnetic phase diagram. Based on first principle
electronic structure calculations we write down a phenomenological model and
solve it under certain approximations to obtain the ground state energy. In the
process we work out the phase diagram of the correlated double exchange model
on a triangular lattice for the specific band structure at hand.Comment: 13 pages, 5 figures, corrected typo
Time-dependent density functional theory: Past, present, and future
Time-dependent density functional theory (TDDFT) is presently enjoying
enormous popularity in quantum chemistry, as a useful tool for extracting
electronic excited state energies. This article discusses how TDDFT is much
broader in scope, and yields predictions for many more properties. We discuss
some of the challenges involved in making accurate predictions for these
properties.Comment: 12 pages, 4 figure
On the density-potential mapping in time-dependent density functional theory
The key questions of uniqueness and existence in time-dependent density
functional theory are usually formulated only for potentials and densities that
are analytic in time. Simple examples, standard in quantum mechanics, lead
however to non-analyticities. We reformulate these questions in terms of a
non-linear Schr\"odinger equation with a potential that depends non-locally on
the wavefunction.Comment: 8 pages, 2 figure
Interplay of magnetism and band topology in EuCaMgBi (x=0, 0.5) from first principles study
Recent discovery of the time reversal symmetry breaking magnetic Weyl
semimetals has created a huge surge of activities in the field of quantum
topological materials. In this work, we have studied systematically the ground
state magnetic order, electronic structure and the interplay between the
magnetic order and band topology in one such materials, EuMgBi (EMB)
and its Ca doped variant using first principles method within the framework of
density functional theory (DFT). The detailed investigation unravels the
existence of different topological phases in this single material which can be
tuned by an external probe such as magnetic field or chemical substitution. Our
DFT calculations including Coulomb correlation (U) and spin-orbit (SO)
interaction within GGA+U+SO approximation confirms that the magnetic ground
state of EMB is A-type Antiferromagnetic (A-AFM) with Eu magnetic moments
aligned along the crystallographic or direction. Although the ground
state of EMB is A-AFM, the Ferromagnetic (FM) state lies very close in energy.
We observe a single pair of Weyl points connecting valence and conduction band
very close to the Fermi level (FL) along -A direction in the FM state
of EuMgBi with Eu moments aligned along crystallographic direction.
On doping 50\% Ca at Eu sites, we observe single pair of Weyl points moving
closer to the FL which is highly desirable for application purposes. Further we
observe that the separation between the Weyl points in the pair decreases in
doped compound compared to that in the parent compound which has direct
consequence on anomalous Hall conductivity (AHC). Our first principles
calculation of AHC shows high peak values exactly at these Weyl points and the
peak height decreases when we dope the system with Ca. Therefore, Ca doping can
be a good external handle to tune AHC in this system.Comment: 9 pages, 12 figure
Semiclassical Electron Correlation in Density-Matrix Time-Propagation
Lack of memory (locality in time) is a major limitation of almost all present
time-dependent density functional approximations. By using semiclassical
dynamics to compute correlation effects within a density-matrix functional
approach, we incorporate memory, including initial-state dependence, as well as
changing occupation numbers, and predict more observables in strong-field
applications.Comment: 4.5 pages, 1 figur
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