Efficient calculation of level alignment at weakly coupled molecule-metal interfaces using substrate screening within the GW approach

The physics of level alignment at molecule-metal interfaces can often be accurately captured by the ab initio GW approach. However, the computational cost for such GW calculations for typical interfaces is significant, given their large system size and chemical complexity. In the past, approximate self-energy corrections constructed from image-charge models have been used to compute level alignment with good accuracy. However, this approach neglects dynamical effects of the polarizability and requires the definition of an image plane. In this work, we propose a new approximation for GW calculations of molecule-metal interfaces, where we greatly simplify the evaluation of the polarizability of the combined system. This is done by first computing the polarizability of each individual system in smaller cells, followed by unfolding and interpolation techniques to efficiently combine these quantities. Overall, this approach greatly reduces the computational cost for GW calculations of level alignment without sacrificing the accuracy. Moreover, this approach captures both dynamical and nonlocal polarization effects without the need to invoke a classical image charge expression. We benchmark our approximation for the case of a benzene molecule physisorbed on Al(111) surface.