Modeling intermolecular Coulombic decay with non-Hermitian real-time time-dependent density functional theory

In this work, we investigate the capability of using real-time time-dependent density functional theory (RT-TDDFT) in conjunction with a complex absorbing potential (CAP) to simulate the intermolecular Coulombic decay (ICD) processes following the ionization of an innervalence electron. We examine the ICD dynamics in a series of non-covalent bonded dimer systems, including H2O-H2O, HF-HF, Ar-H2O, Ne-H2O and Ne-Ar. We consider an initial state generated from an inner-valence excitation on either monomer within each dimer, as the monomers are symmetrically not equivalent. In comparison to previous RT-TDDFT studies, we show that RT-TDDFT simulations with a CAP correctly capture the ICD phenomenon in systems exhibiting a stronger binding energy. The calculated time-scales for ICD of the studied systems are in the range of 5-50 fs in agreement with previous studies. However, there is a break-down in the accuracy of the methodology for the more weakly bound, pure van der Waals bonded systems. The accuracy in the former is attributed to both the use of the CAP and the choice of a long-range corrected functional with diffuse basis functions. The benefit of the presented real-time methodology is that it provides direct time-dependent population information without necessitating any a-priori assumptions about the electronic relaxation mechanism. As such, the RT-TDFFT/CAP simulation protocol provides a powerful tool to differentiate between competing electronic relaxation pathways following inner-valence or core ionization.