Because the FM model is expressed by the Ising model, the lower-energy states of the FM can be effectively obtained using quantum annealers and Ising machines. Indeed, this algorithm has been widely used to solve BBO problems in materials science and chemistry. For example, the FMQA algorithm was adopted to optimize the atomic configurations of the magnesium and germanium ions in a magnetic tunnel junction structure, and its efficiency was confirmed for small problems. Furthermore, its application in crystal structure prediction has also been considered. In this study, the FMQA algorithm combined with the Vienna Ab Initio Simulation Package (VASP) is employed to effectively search for stable proton configurations in PCFCs (Figure ).