This paper reports ab initio calculations of the phonon dispersion relations of single-layer and bulk dichalcogenides MoS₂ and WS₂. The study focuses on the behavior of Raman-active modes A₁g and E₂g¹ as a function of the number of layers. The results show that the A₁g mode increases in frequency with increasing layers, while the E₂g¹ mode decreases. This decrease is attributed to enhanced dielectric screening of long-range Coulomb interactions between effective charges with more layers. The long-range part of the interaction dominates, overcompensating for the short-range interaction increase due to weak interlayer forces. The paper discusses the phonon dispersion relations of single-layer and bulk MoS₂ and WS₂, comparing them with experimental data. It presents a detailed ab initio study of the phonon dispersion relations and the evolution of Raman-active phonon modes with the number of layers. The results show that the A₁g mode frequency increases with more layers, while the E₂g¹ mode frequency decreases. This is explained by the dielectric screening of long-range Coulomb interactions in bulk MoS₂. The study also compares the phonon dispersions of single-layer and bulk MoS₂ and WS₂, showing that the phonon frequencies of WS₂ are generally lower than those of MoS₂ due to the larger mass of tungsten atoms. The paper concludes that the decrease in the E₂g¹ mode frequency is due to stronger dielectric screening of long-range Coulomb interactions in few-layer and bulk MoS₂. The results are consistent with experimental observations and provide insights into the behavior of phonon modes in layered materials.This paper reports ab initio calculations of the phonon dispersion relations of single-layer and bulk dichalcogenides MoS₂ and WS₂. The study focuses on the behavior of Raman-active modes A₁g and E₂g¹ as a function of the number of layers. The results show that the A₁g mode increases in frequency with increasing layers, while the E₂g¹ mode decreases. This decrease is attributed to enhanced dielectric screening of long-range Coulomb interactions between effective charges with more layers. The long-range part of the interaction dominates, overcompensating for the short-range interaction increase due to weak interlayer forces. The paper discusses the phonon dispersion relations of single-layer and bulk MoS₂ and WS₂, comparing them with experimental data. It presents a detailed ab initio study of the phonon dispersion relations and the evolution of Raman-active phonon modes with the number of layers. The results show that the A₁g mode frequency increases with more layers, while the E₂g¹ mode frequency decreases. This is explained by the dielectric screening of long-range Coulomb interactions in bulk MoS₂. The study also compares the phonon dispersions of single-layer and bulk MoS₂ and WS₂, showing that the phonon frequencies of WS₂ are generally lower than those of MoS₂ due to the larger mass of tungsten atoms. The paper concludes that the decrease in the E₂g¹ mode frequency is due to stronger dielectric screening of long-range Coulomb interactions in few-layer and bulk MoS₂. The results are consistent with experimental observations and provide insights into the behavior of phonon modes in layered materials.