  We examined energy spectrums of some particular systems of binary spins. It
is shown that the configuration space can be divided into classes, and in the
limit the energy distributions in these classes can be approximated by the
normal distributions. For each class we obtained the expressions for the first
three moments of the energy distribution, including the case of presence of a
nonzero inhomogeneous magnetic field. We also derived the expression for the
variance of the quasienergy distribution in the local minimum. We present the
results of computer simulations for the standard Ising model and the
Sherrington-Kirkpatrick and Edwards-Anderson models of spin glass. Basing on
these results, we justified the new method of the partition function
calculation.
