A computational procedure is proposed for calculating the lattice energy of molecular crystals using the ab initio MO method. Our method does not require any adjustable parameters and provides a general description for various molecular crystals including electron donor-acceptor (EDA) complexes. Using the method, the packing structure of H3N-BF3 crystal was optimized at the HF/3-21 + G level and the lattice energy was calculated at the MP2/6-311 + G* level. The calculation reproduced the experimental lattice constants with reasonable accuracy. Moreover, the structural feature of the H3N-BF3 crystal was discussed based on the molecular interactions in the crystal. (C) 2003 Elsevier Science B.V. All rights reserved.