Calculating excitation energies by extrapolation along adiabatic connections
Abstract
In this paper, an alternative method to rangeseparated linearresponse timedependent densityfunctional theory and perturbation theory is proposed to improve the estimation of the energies of a physical system from the energies of a partially interacting system. Starting from the analysis of the Taylor expansion of the energies of the partially interacting system around the physical system, we use an extrapolation scheme to improve the estimation of the energies of the physical system at an intermediate point of the rangeseparated or linear adiabatic connection where either the electronelectron interaction is scaled or only the longrange part of the Coulomb interaction is included. The extrapolation scheme is first applied to the rangeseparated energies of the helium and beryllium atoms and of the hydrogen molecule at its equilibrium and stretched geometries. It improves significantly the convergence rate of the energies toward their exact limit with respect to the rangeseparation parameter. The rangeseparated extrapolation scheme is compared with a similar approach for the linear adiabatic connection, highlighting the relative strengths and weaknesses of each approach.
 Publication:

Physical Review A
 Pub Date:
 March 2015
 DOI:
 10.1103/PhysRevA.91.032519
 arXiv:
 arXiv:1503.05693
 Bibcode:
 2015PhRvA..91c2519R
 Keywords:

 31.15.A;
 31.15.E;
 31.50.Df;
 Ab initio calculations;
 Densityfunctional theory;
 Potential energy surfaces for excited electronic states;
 Physics  Chemical Physics;
 Condensed Matter  Other Condensed Matter
 EPrint:
 to appear in Phys. Rev. A