54 research outputs found
An accurate exchange energy functional in excited-state density functional theory
An exchange energy functional is proposed and tested for obtaining a class of
excited-state energies using density-functional formalism. The functional is
the excited-state counterpart of the local-density approximation functional for
the ground-state. It takes care of the state-dependence of the energy
functional and leads to highly accurate excitation energies.Comment: 19 pages. 2 figures. Submitted to PR
A general penalty method for density-to-potential inversion
A general penalty method is presented for the construction of of Kohn-Sham
system for given density through Levy's constrained-search. The method uses a
functional of one's choice. Different forms of are employed
to calculate the kinetic energy and exchange-correlation potential of atoms,
jellium spheres, and Hookium and consistency among results obtained from them
is shown
A study of accurate exchange-correlation functionals through adiabatic connection
A systematic way of improving exchange-correlation energy functionals of
density functional theory has been to make them satisfy more and more exact
relations. Starting from the initial GGA functionals, this has culminated into
the recently proposed SCAN(Strongly constrained and appropriately normed)
functional that satisfies several known constraints and is appropriately
normed. The ultimate test for the functionals developed is the accuracy of
energy calculated by employing them. In this paper, we test these
exchange-correlation functionals -the GGA hybrid functionals B3LYP and PBE0,
and the meta-GGA functional SCAN- from a different perspective. We study how
accurately these functionals reproduce the exchange-correlation energy when
electron-electron interaction is scaled as scaling parameter times Vee with
this parameter varying between 0 and 1. Our study reveals interesting
comparison between these functionals and the associated difference Tc between
the interacting and the non-interacting kinetic energy for the same density.Comment: 8 Pages, 3 Figures and 8 Table
Hydrodynamic approach to TDDFT; response properties of metal clusters
Performing electronic structure calculations for large systems, such as
nanoparticles or metal clusters, via orbital based Hartree-Fock or Kohn-Sham
theories is computationaly demanding. To study such systems, therefore, we have
taken recourse to the hydrodynaic approach to time-dependent density functonal
theory. In this paper we develop variation-perturbation method within this
theory in terms of the particle and the current densities of a system. We then
apply this to study the linear and nnlinear resonse properties of alkali metal
clusters within spherical jellium backgrond model.Comment: 28 pages and 5 figures in eps format, revised and new references and
figures added. resubmitted to Journal of Chemical Physic
Comparison of van der Waals coefficient C of sodium clusters obtained via spherical jellium background model and all-electron ab-initio method
In this paper we employ two distinct approaches - all-electron \textit{ab
initio} method and the spherical jellium background model- within time
dependent density functional theory to calculate the long range dipole-dipole
dispersion coefficient (van der Waals coefficient) of sodium atom
clusters containing even number of atoms ranging from 2 to 20 atoms. The
dispersion coefficients are obtained via Casimir-Polder relation. All the
calculations are carried out with local density approximation for
exchange-correlation energy functional. These two sets of results are compared
to assess the accuracy of jellium based results and to ascertain the effect of
detail ionic structure of the clusters on the van der Waals coefficient.Comment: 15 pages including 2 figures. To be published in Journal of
Computational Methods in Science and Engineerin
Accurate exchange energy and total energy for excited states: Inclusion of gradient correction
We present an approach for accurate calculation of exchange energy and total
energy for excited states using time independent density functional formalism.
This is done by inclusion of gradient correction into the excited state
exchange energy functionals developed by us. We have incorporated Becke and
Perdew Wang corrections into our functional and have studied various types of
excited states having one and two gaps in occupation of orbitals
Local density approximation for exchange in excited-state density functional theory
Local density approximation for the exchange energy is made for treatment of
excited-states in density-functional theory. It is shown that taking care of
the state-dependence of the LDA exchange energy functional leads to accurate
excitation energies
Frequency dependent hyperpolarizabilities of atoms; calculations using density-functional theory
Using the orbitals generated by the van Leeuwen-Baerends potential, we
calculate frequency dependent response properties of noble gas atoms of He, Ne
and Ar and alkaline earth atoms Be and Mg, with particlar emphasis on their
nonlinear polarizabilities. For this we employ time-dependent Kohn-Sham
formalism with adiabatic local-density aproximation (ALDA) for exchange and
correlation. We show that results thus obtained for frequency dependent
polarizabilities of the inert gas atoms are highly acurate. On the other hand,
polarizabilities of the alkaline earths are not given with the same accuracy.
In light of this, we make an assessment of ALDA for obtaining linear and
nonlinear response properties by employing time-dependent density-functional
theory.Comment: 13 pages of text and 7 figure
Calculation of van der Walls coefficients of alkali metal clusters by hydrodynamic approach to time-dependent density-functional theory
In this paper we employ the hydrodynamic formulation of time-dependent
density functional theory to obtain the van der Waal coefficients and
of alkali-metal clusters of various sizes including very large
clusters. Such calculation becomes computationally very demanding in the
orbital-based Kohn-Sham formalism, but quite simple in the hydrodynamic
approach. We show that for interactions between the clusters of same sizes,
and sale as the sixth and the eighth power of the cluster
radius rsepectively, and approach the respective classically predicted values
for the large size clusters.Comment: 13 pages with two figures. Submitted to J. Phys. B: At. Mol. Opt.
Phy
Study of adiabatic connection in density functional theory with an accurate wavefunction for 2-electron atoms
Using an accurate semi-analytic wavefunction for two electron atoms, we
construct the external potential for varying strength of electron-electron
(e-e) interaction. Using this potential we explicitly calculate the energy of
their positive ion and show that the ionization-potential of these systems
remains unchanged with respect to the strength parameter for e-e interaction.
Furthermore, using total energies of these systems as a function of strength
parameter, we provide a new perspective into a variety of hybrid functionals.Comment: 6 Pages, 4 Figures and 2 Table
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