In this study, the primary aim is to enhance the computational analysis of Tetrachlorobutadiene (TCBD) isomers by incorporating Density Functional Theory (DFT) with the B3LYP functional. The research builds upon previous work, which primarily utilized the Hartree-Fock (HF) method, and seeks to overcome its limitations in accurately predicting molecular properties, particularly in systems with complex electron correlation effects. DFT, with its ability to include electron correlation beyond the mean-field approximation, provides a more robust and precise approach for molecular analysis. The study has several specific objectives. First, it aims to optimize the molecular geometries of nine different TCBD isomers, each with varying configurations of hydrogen and chlorine atoms, using advanced DFT methods. Second, the research seeks to compute the vibrational frequencies of these isomers and simulate their infrared (IR) spectra using the B3LYP and B3LYP-D3BJ functionals. These functionals are chosen due to their balance of computational efficiency and accuracy, particularly in capturing electron correlation and dispersion interactions. A key goal of the study is to compare the performance of DFT with the HF method in identifying functional groups and predicting the molecular structures of the TCBD isomers. By conducting a comparative analysis of the IR spectra generated by both methods, the study aims to demonstrate the superiority of DFT in terms of accuracy and consistency. This research ultimately seeks to provide a more reliable computational framework for analyzing chlorinated organic compounds like TCBD, which are of significant interest due to their environmental and chemical properties. Additionally, the study aims to validate the DFT-based computational model by comparing the simulated IR spectra with experimental data, ensuring the robustness of the findings.