Excitation energies in the energy density method

J. Hevesi, E. Lehotski, E. Balint

Leslie L. Foldy

The ground state energy and elementary excitations of a charged gas of bosons at high densities are examined by use of the method developed by Bogoliubov for boson gases. It is conjectured, but not herein established, that this method yields exact results in the high-density limit analogous to those obtained by Gell-Mann and Brueckner, and by Sawada, in the corresponding case of a charged fermion gas. The ground state energy is essentially correlation energy, and is therefore negative, and its magnitude varies as the one-fourth power of the density at high densities. The elementary excitations have for low momenta the energy appropriate to plasma waves, and for high momenta the energy appropriate to single-particle excitation. There is therefore an energy gap, suggesting that the gas is both a superfluid and a superconductor at low temperatures. At low densities the behavior of a charged gas is independent of statistics; hence, such a gap must disappear as the system is expanded.

Xue Jiang

The energy density of the ground state and excitation spectrum in Spin-Peierls Systems with s=12xxz antiferromagnetic chain are given by means of the bosonization self-consistent perturbation method.The change of the energy density of the ground state and quasipartical excited energy gap with the distortion and anti-isotropy of the model is discussed.

Ezekiel Oyeniyi, Omololu Akin-Ojo

The semi-empirical INDO/s method is popular for studies of excitation energies and absorption of molecules due to its low computational requirement, making it possible to make predictions for large systems. However, its accuracy is generally low, particularly, when compared with the typical accuracy of other methods such as time-dependent density functional theory (TDDFT). Here, we present machine learning (ML) models that correct the INDO/s results with negligible increases in the amount of computing resources needed. While INDO/s excitations energies have an average error of about 1.1 eV relative to TDDFT energies, the added ML corrections reduce the error to 0.2 eV. Furthermore, this combination of INDO/s and ML produces UV-Vis absorption spectra that are in good agreement with the TDDFT predictions.

Joachim Alexander Maruhn, P.‐G. Reinhard, E. Suraud

D. ter Haar, W. E. Parry