The study focuses on investigating the properties of AB 2 transition metal dichalcogenides (TMDCs), where A represents Nb and Ta, and B represents S, Se, and Te. Therefore, a total of 06 unique combinations of A and B elements are considered. Each combination exhibits two distinct phases, namely the 1T and 2H phases, resulting in a total of 12 systems under investigation. The objective of this research is to conduct a comprehensive analysis of these systems, including geometry optimization, total energy calculations, electronic band structure analysis, Fermi surface characterization, and phonon calculations . Both spin-orbit coupling (SOC) and non-SOC (NSOC) cases are considered in these calculations. To ensure accurate results for the aforementioned calculations, four different exchange-correlation functionals are employed, namely LDA, PBE, PBESol, and SCAN. These functionals are chosen for their ability to provide reliable ab initio calculations. Additionally, five different van der Waals (vdW) corrections are applied to the systems, including optB88-vdW, optPBE-vdW, vdW-DF2, rev-vdW-DF2, and SCAN+rVV10. By incorporating these vdW corrections, the impact of weak interlayer interactions on the properties of the TMDC systems can be accurately captured. Considering both the 1T and 2H phases for each of the 06 TMDC systems, a total of 12 sets of calculations are performed. Consequently, each TMDC system requires 18 sets of calculations to comprehensively analyze both phases. The detailed geometry structure of the systems is provided below, serving as a valuable reference for the subsequent analyses and discussions in this study. All the geometry optimization calculations and energy calculations have been performed and completed for all the systems in NSOC case and the results are shown below in tabular form (Table ). Based on the observations from the table above, it is evident that the energy difference between the 1T and 2H phases falls within the positive range, indicating the stability of the 2H phase over the 1T phase. This finding is consistent with previous reports , providing further support for the reliability of our results. However, it is worth noting that TaTe2 demonstrates an interesting behavior, where the 1T phase is found to be more stable than the 2H structure (1T-2H < 0) specifically for the PBESol functional. This deviation from the overall trend is unique to TaTe2 and distinguishes it from the other systems analyzed. To gain further insights into the structural parameters of the TMDC materials, detailed analyses were conducted following geometry optimization for all the XC functionals and vdW-DFs. The results are summarized for PBESol XC functional in the table provided below (Table ). In the NSOC case, the performance assessment of various exchange-correlation (XC) functionals reveals that PBESol emerges as the overall effective functional for the TMDC materials.