I want to calculate $\Delta H$ for hydrogenation of benzene and producing cyclohexane using MM+ Force Field Energy. I am using Hyperchem for energy calculation and optimization. I calculated the energy for cyclohexane and then I calculated the energy for benzene. But the difference of two energies is totally false. The calculated energy is $8~\mathrm{kcal/mol}$ however the real value is $-49~\mathrm{kcal/mol}$.
Is it a true way to calculate $\Delta H$? If not, how can I do it ?