Coupled cluster methods are considered among the most accurate tools in electronic structure theory to obtain ground state properties and spectroscopic properties. Nonetheless, their application to the high-energy region, specifically to describe the core-excitation phenomena that are behind spectroscopic techniques like XAS and XCD are very limited. We present here an implementation of damped response theory based on an asymmetric Lanczos algorithm within Coupled Cluster theory for the CCS, CC2 and CCSD approximations, We apply it to the simulation of the K-edge X-ray absorption spectra of the closed-shell 10-electron systems Neon, CH4, H2O, HF and NH3. The effect of triple excitations on the excitation energies is estimated by means of the CCSDR(3) approximation. Results are compared with experiment as well as results obtained with other computational methods, in particular the Hartree-Fock STEX approach.
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