The decoupling transformation method as applied to lattice vibrations is reformulated in terms of the concept of partitioning crystals into regions with periodic boundary conditions—cyclic regions. Values of force constants for the hexamethylenetetramine system are determined using the decoupling transformation scheme which are consistent with results in the literature. An interpolation formula and its modification are established for constructing the lattice dynamical maxtix of molecular crystals and applied successfully to the above physical system as well. More aspects of the decoupling transformation are pointed out in detail. Copyright © 1986 American Institute of Physics.