Complete lattice dynamical behaviour of ND4Cl as well TlCl have been studied with the help of new phenomenological model, van der Waals three-body force shell model (VTSM), incorporating the effect of van der Waals interactions (vWI) along with long-range screened Coulomb and three-body interactions (TBI) in the frame work of rigid shell model where short range interactions are operative up to the second neighbour in these halides. This new model presents an excellent agreement with available experimental data and a vast improvement for the theoretical available data for phonon dispersion curve (PDCs) for [q00], [qq0] and [qqq] directions in case , variation of Debye Temperature Curve and combined density state (CDS) curve and anharmonic properties such as third and fourth order elastic constants and pressure derivative of second order elastic constants. It is observed this new model presents an excellent agreement with available experimental data and a vast improvement for the theoretical available data for phonon dispersion curve (PDC), variation of Debye Temperature Curve and combined density state (CDS) curve and anharmonic properties such as third and fourth order elastic constants and pressure derivative of second order elastic constants. It is believed that incorporation of van der Waals interaction enables us to produce a vast study of lattice dynamical and other derivable properties. A good agreement has been obtained between experimental and VTSM values for dependant properties.