We have implemented the algorithms for CpHMD with charge interpolation in a fork of GROMACS software package (2021 release). The code and manuals are available for free at . Here we verify the validity of our implementation for reproducing pK a values of peptides and proteins. To demonstrate that the linear interpolation of charges (equation 17) scales better with the number of titratable sites in the system than the linear interpolation of interaction functions (equation 15), we compared the scaling between our new implementation, which is based on linear charge interpolation on the one hand, and a previous implementation in a fork of the GROMACS 3.3 release, which is based on linear interpolation of the force field potentials on the other hand. To estimate the additional computational effort required for performing CpHMD with the new implementation, we also compared the performance of a CpHMD simulation to that of a normal MD simulations on both CPUs and GPUs.