arXiv subjects

A. B. F. da Silva

Publications and source records attributed to A. B. F. da Silva.

4 recordsLinked to original sources

arXiv2009

Excitation energies from ground-state density-functionals by means of generator coordinates

The generator-coordinate method is a flexible and powerful reformulation of the variational principle. Here we show that by introducing a generator coordinate in the Kohn-Sham equation of density-functional theory, excitation energies can be obtained from ground-state density functionals. As a viability test, the method is applied to ground-state energies and various types of excited-state energies of atoms and ions from the He and the Li isoelectronic series. Results are compared to a variety of alternative DFT-based approaches to excited states, in particular time-dependent density-functional theory with exact and approximate potentials.

physics.chem-ph↗

arXiv2007

Simple quantitative estimate of the derivative discontinuity of the exchange-correlation functional in atoms and molecules

The derivative discontinuity of the exchange-correlation functional of density-functional theory is cast as the difference of two types of electron affinities. We show that standard Kohn-Sham calculations can be used to calculate both affinities, and that their difference benefits from substantial and systematic error cancellations, permitting reliable estimates of the derivative discontinuity. Numerical calculations for atoms and molecules show that the discontinuity is quite large (typically several eV), and significantly and consistently improves the agreement of the calculated fundamental energy gap with the experimental gaps. The percentage error of the single-particle gap is reduced in favorable cases by more than one order of magnitude, and even in unfavorable cases by about a factor of two.

physics.chem-ph↗

arXiv2007

The generator coordinate method in time-dependent density-functional theory: memory made simple

The generator coordinate (GC) method is a variational approach to the quantum many-body problem in which interacting many-body wave functions are constructed as superpositions of (generally nonorthogonal) eigenstates of auxiliary Hamiltonians containing a deformation parameter. This paper presents a time-dependent extension of the GC method as a new approach to improve existing approximations of the exchange-correlation (XC) potential in time-dependent density-functional theory (TDDFT). The time-dependent GC method is shown to be a conceptually and computationally simple tool to build memory effects into any existing adiabatic XC potential. As an illustration, the method is applied to driven parametric oscillations of two interacting electrons in a harmonic potential (Hooke's atom). It is demonstrated that a proper choice of time-dependent generator coordinates in conjunction with the adiabatic local-density approximation reproduces the exact linear and nonlinear two-electron dynamics quite accurately, including features associated with double excitations that cannot be captured by TDDFT in the adiabatic approximation.

cond-mat.mes-hall↗

arXiv2004

Energy lowering of current-carrying single-particle states in open-shell atoms due to an exchange-correlation vector potential

Current-density-functional theory is used to perturbatively calculate single-particle energies of open-shell atoms prepared in a current-carrying state. We focus on the highest occupied such energy, because its negative is, in principle, the exact ionization energy. A variety of different density functionals and calculational schemes are compared with each other and experiment. When the atom is prepared in a current-carrying state, a current-dependent exchange-correlation functional is found to slightly lower the single-particle energy of the current-carrying orbital, as compared to a calculation using standard (current independent) density functionals for the same system. The current-dependent terms in the exchange-correlation functional thus provide additional stabilization of the current-carrying state.

physics.chem-ph↗