Chemical substitution can tune $1T\text{−}\text{Ta}{\mathrm{S}}_2$ from the commensurate charge-density-wave (CCDW) phase to the nearly commensurate CDW phase (NCCDW), but the microscopic mechanism remains unclear. Using first-principles calculations, we compare two prototypical cases: Se-for-S and Ti-for-Ta substitutions, which reveal dopant site selectivity as the key difference. We show that the CCDW-to-NCCDW phase transition can be understood from the angle of domain wall (DW) formation. The trend can be rationalized by the competition between the energy gain from locally reregistering the SD pattern around quenched dopants and the cost of creating DWs. A statistical estimation based on the first-principles relative substitution energy and DW formation energy captures the much lower critical concentration for Ti than for Se to create DWs. Isolated Se- or Ti-substituted SD clusters remain insulating, whereas DW reconstruction generates metalliclike low-energy spectral weight. This comparison indicates that the metallic behavior experimentally associated with the CCDW-to-NCCDW transition originates primarily from DW regions rather than from direct dopant-induced metallization.

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• Charge density waves
• Doping effects
• Transition metal dichalcogenides
• Density functional theory