We present a comprehensive first-principles investigation of defects in $4H_b\text{−}{\mathrm{TaS}}_2$. In this layered transition metal dichalcogenide, charge transfer between alternating Mott-insulating 1T and metallic 1H layers gives rise to exotic quantum phases such as the Kondo effect and topological superconductivity. Motivated by recent defect manipulation in $4H_b\text{−}{\mathrm{TaS}}_2$ via STM, we address their microscopic nature and impact on interlayer charge transfer. To this end, we systematically analyze over 90 defects using large-scale density functional theory (DFT) calculations. Our analysis identifies 1H sulfur vacancies, Ta-on-S antisites, and Ta interstitials as the most likely origins of the commonly observed defects, with Ta-on-S antisites producing the strongest charge-transfer modulation. Our extensive dataset, compiled from STM simulations, defect formation energies, work functions, and charge transfer, establishes a foundational resource for future theoretical and experimental studies on defect engineering in $4H_b\text{−}{\mathrm{TaS}}_2$.

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• Charge density waves
• Defects
• Electronic structure
• Layered crystals
• Density functional calculations