Coupled cluster methods are considered among the most accurate tools in electronic
structure theory. Nonetheless relatively limited attempt seems to have been made to
extend their applicability to the description of the core-excitation phenomena that are
behind largely used spectroscopic techniques like x-ray absorption spectroscopy and
x-ray circular dichroism.
As a first step to redeem for such situation, we present an implementation of damped
response theory (aka complex polarization propagator approach) based on an
asymmetric Lanczos algorithm for the CCS, CC2 and CCSD hierarchy of coupled
cluster methods, and apply it to the simulation of the K-edge x-ray absorption spectra of
various closed-shell systems, including Neon, CH4, H2O, HF and CO [1]. Triple
excitation effects on the excitation energies are estimated by means of the CCSDR(3)
approximation, and relativistic effects are accounted for using the Douglas-Kroll
approach. Results are compared with experiment as well as results obtained with other
computational methods.
[1] S. Coriani, T. Fransson, O. Christiansen, P. Norman, P. Decleva. Work in progress.
