TheQDPT CI approach for excitation and ionization spectra: A test on the CO molecule

Abstract

A detailed analysis of the performance of the QDPT CI method, which is based on the application of quasi-degenerate perturbation theory (QDPT) within the configuration interaction (CI) approach, is presented by comparing the QDPT CI results and those obtained from the diagonalization of the perturbative space. Calculations of core and valence excitation and ionization spectra of the CO molecule, which is a strongly correlated system, are carried out using a DZ basis set and the accuracy of the eigenvalues and eigenfunctions is checked through the comparison of excitation and ionization energies and intensities. Excellent agreement is obtained for all values, indicating the computational advantages of QDPT CI which is able to explore wide energy ranges without requiring the diagonalization of large spaces. © 1995 John Wiley & Sons, Inc.