The evaluation of Koopmans functionals is a subject of common interest for the scientific community, as it has been proved that by using them it is possible to correct DFT theory predictions with accuracy in line with the state-of-the-art many-body perturbation theory (GW), which on the other hand is exceedingly expensive to be considered a good alternative. To correctly predict materials properties, it is needed to calculate these functionals totally ab initio, and this includes the well-known problem in numerical analysis of the solution of a linear system of type A x = b, where the matrix A can have extremely big dimensions to be treated without any advanced high-performance methodology. In this case, it becomes necessary to port the code on GPUs to obtain an acceleration of the main demanding routines of the program. In this work, we show the result of porting to GPU the code KCW [1], part of the package Quantum ESPRESSO, thanks to an API with SIRIUS [2], a domain-specific library for electronic-structure calculations. The flexibility of SIRIUS is used to run the code both on AMD and NVIDIA GPUs.[1] N. Colonna et al., JCTC 18, 5435-5448 (2022)[2] https://github.com/electronic-structure/SIRIUS