Normal modes of solids HF, HCl and polyethylene having the exciting spectrometric phenomena have been evaluated by taking the lowest temperature phase of these species in the solid. The solids HF and HCl have the same space group as C$_{2}{ u}$, and polyethylene has a space group with D$_{2h}$. The normal modes were obtained by the valence force field with modified force constants and a quantitative description of the normal mode is adjusted by the potential energy distribution (PED). From the PED, the most fittable force constants are also obtained. We have intended to calculate the normal modes by using the smallest size of the model and the simple computational process. To remove the edge effects being occurred in constructing the single cluster model, different from the boundary condition being generally used up to now, the idea of pseudolattice method being successfully applied to MO calculations of solid was extended to normal mode analysis in order to give the same environment for all moecules in a chosen cluster. By using the above valence force field and boundary condition, we obtain the assigned frequencies and compare those results with the results obtained by others.