The system I am studying is photosystem 2, which has four manganese. When using easyspin to draw the energy level diagram, matlab prompts that there is insufficient memory. When using matrix diagonalization to simulate the EPR spectrum, it also prompts that there is insufficient memory. But perturbation theory does not work for electron spins with S>1/2.I want to simulate the energy level diagram and EPR spectrum, but the system has four nuclei.Is there any way to solve the problem of insufficient memory?