On the Kohn-Sham density response in a localized basis set

Abstract

We construct the Kohn-Sham density response function 0 in a previously described basis of the space of orbital products. The calculational complexity of our construction is O (N2 Nω) for a molecule of N atoms and in a spectroscopic window of Nω frequency points. As a first application, we use χ0 to calculate the molecular spectra from the Petersilka-Gossmann-Gross equation. With χ0 as input, we obtain the correct spectra with an extra computational effort that grows also as O (N2 Nω) and, therefore, less steeply in N than the O (N3) complexity of solving Casida's equations. Our construction should be useful for the study of excitons in molecular physics and in related areas where χ0 is a crucial ingredient. © 2009 American Institute of Physics.