The lattic energy (U) of naphthalene and anthracene crystals as a function of the unit cell volume (v) has been calculated by the atomatom potential method. The experimental thermal expansion tensor has been used in this calculation. The first and the second derivatives of the lattice energy with respect to the unit cell volume have been obotained from the curveU(v>. Methods of comparison of these values with experimental data on the crystal internal energy and its volum, e derivatives and also ways of calculating the vibrational part of the crystal internal energy have been discussed. It has been shown that vibrational corrections to the lattice energy and its volume derivatives are small.