A periodic density functional theory method using the B3LYP hybrid exchange-correlation potential is applied to the Prussian blue analogue RbMn[Fe(CN)(6)] to evaluate the suitability of the method for studying, and predicting, the photomagnetic behavior of Prussian blue analogues and related materials. The method allows correct description of the equilibrium structures of the different electronic configurations with regard to the cell parameters and bond distances. In agreement with the experimental data, the calculations have shown that the low-temperature phase (LT; Fe2+(t(2g)(6), S = 0)-CN-Mn-3+(t(2g)(3)e(g)(1), S = 2)) is the stable phase at low temperature instead of the high-temperature phase (HT; Fe3+(t(2g)(5), S = 1/2)-CN-Mn2+(t(2g)(3)e(2)g, S = 5/2)). Additionally, the method gives an estimation for the enthalpy difference (HT double left right arrow LT) with a value of 143 J mol(-1) K-1. The comparison of our calculations with experimental data from the literature and from our calorimetric and X-ray photoelectron spectroscopy measurements on the Rb0.97Mn[Fe(CN)(6)](0.98)center dot 1.03H(2)O compound is analyzed, and in general, a satisfactory agreement is obtained. The method also predicts the metastable nature of the electronic configuration of the high-temperature phase, a necessary condition to photoinduce that phase at low temperatures. It gives a photoactivation energy of 2.36 eV, which is in agreement with photoinduced demagnetization produced by a green laser.