The determination of the susceptibility for very large systems is limited by the available memory (RAM). This is because the size of the matrix containing M_s elements increases rapidly with the increase in the number of unpaired electrons and paramagnetic centres. The total number of elements in the matrix containing the M_s elements can be given as [(no. of unpaired electrons on centre 1) * (no. of unpaired electrons on centre 2) * (no. of unpaired electrons on centre 3) * ……...]². For example, for a {Mn^III₄} system, the matrix contains a total of (5*5*5*5)² =) 390,625 elements, for a {Mn^III₅} system, the matrix contains a total of (5⁵*5⁵ =) 9,765,625 elements while for a {Mn^III₆} system, the matrix contains (5⁶*5⁶ =) 244,140,625 elements. Since the calculation of susceptibility requires the exact diagonalisation of the whole matrix, the matrix needs to be stored in the memory and hence the limitation.