An embedding scheme for constraint-based orbital-optimized excitations in molecular and bulk environments

We recently presented a novel approach to variationally determine electronically excited states based on constrained density functional theory calculations. The constraint-based orbital-optimized excited state method (COOX) [Kussmann <i>et al.</i>, <i>J. Chem. Theory Comput.</i>, 2024, <b>20</b>, 8461-8473] allows the evaluation of arbitrary electronic excitations and has several advantages compared to other methods like ΔSCF. In this work, we present an embedding scheme for COOX where the constraint potential is drawn from a sub-system calculation. This approach enables the accurate evaluation of specific excited states within complex environments that are difficult to obtain with conventional methods. The validity and range of applicability of the presented method are investigated for first exemplary calculations.