Groundwater contamination is a significant issue to the environment and human health worldwide. The common groundwater contaminants include organic chlorinated compounds, pesticides, nitrates, trace metals and antibiotics. To remove the contaminant from the groundwater, significant efforts have been made to explore nanoscale zero-valent iron (nZVI) as a potential remediation method. nZVI can be injected into the permeable reactive barrier (PRB) which can be placed into the groundwater table to remove contaminants via reduction, adsorption, precipitation, or a combination of these processes. While experimental studies have been conducted to explain observed phenomena, critical knowledge gaps about the accurate atomic understanding of the properties of nZVI and their remediation mechanisms persist, such as no correct consideration of van der Waals (vdW) corrections during the theoretical study, inaccurate representative atomic models of nZVI, and a lack of understanding of the impact of solvent and modifications of nZVI on their remediation mechanism. [...]