Multilayer Approach to the IP-EOM-DLPNO-CCSD Method: Theory, Implementation, and Application

We present a multilayer implementation of the EOM-CCSD for the computation of ionization potentials of atoms and molecules in the presence of their environment. The method uses local orbitals to partition the system into a number of hypothetical fragments and treat different fragments of the system at different levels of theory. This approach significantly reduces the computational cost with a systematically controllable accuracy and is equally applicable to describe the environmental effect of both bonded and nonbonded nature. An accurate description of the interfragment interaction has been found to be crucial in determining the accuracy of the calculated IP values.