In order to explore the phase space by using MC simulations, translations were performed both on ions and water while rotations were applied only to water molecules, in a ratio of 1:1:1 respectively. NCMC moves are performed less frequently than these "standard" MC moves so that the relative probability to perform NCMC moves was set to 10 -3 . The reason is that ion insertion/deletion achieved during a NCMC move would appear less frequently than simple MC moves to rotate or translate a chosen particle. Also, short MD steps performed during alchemical transformation of water molecules into ions (or vice versa) accounts also for collective motion of particles to accommodate insertion of water (or ions). Consequently, the execution time of a NCMC move is much higher than the execution time of a "standard" MC move, as discussed below. In our validation of the method, we considered systems containing at most 150 molecules to keep the computational cost reasonable, due to the sequential nature of the RASPA code.