Core Binding Energy Calculations: A Scalable Approach with Quantum Embedding based EOM-CC Method

We investigate the use of density matrix embedding theory to facilitate the computation of core ionization energies (IP) of large molecules at the equation of motion coupled-cluster singles doubles with perturbative triples (EOM-CCSD*) level in combination with the core-valence separation (CVS) approximation. The unembedded IP-CVS-EOM-CCSD* method with a triple-ζ basis set produces ionization energies within < 1 eV of experiment with a standard deviation of about 0.2 eV for the core65 dataset. The embedded variant contributes very little systematic error relative to the unembedded method, with a mean unsigned error of 0.07 eV and a standard deviation of about 0.1 eV, in exchange for accelerating the calculations by many orders of magnitude. By employing embedded EOM-CC methods, we computed the core-ionization energies of uracil-hexamer, doped fullerene, and chlorophyll molecule, utilizing up to ∼4000 basis functions within < 1 eV from experimental values. Such calculations are not currently possible with unembedded EOM-CC method.