Investigating Chlorination and Migration Mechanism of NaCl on C−S−H: DFT and AIMD Study**

Abstract The present study investigates the chlorination and migration mechanism of Tobermorite9 Å through the use of density functional theory (DFT) calculation and ab initio molecular dynamics (AIMD). The findings reveal a negative adsorption energy value of −2.19488 eV. The results of the charge density difference analysis reveal that the Ca atoms experience electron loss, while the Cl atom undergoes electron gain. The O atom situated at the end of the silicate chain (and silicate chain bridge) exhibits electron gain, and the Na atom experiences electron loss. The results of density of states (DOS) and partial density of states (PDOS) demonstrate that the Ca−Cl bond was created as a result of the interaction between Ca and Cl orbitals. The evident overlaps between Na‐p and O24‐p orbitals lead to the formation of Na−O bond. In AIMD simulation, the minimum energy barrier and activation energy of sodium chloride molecule are 0.09236 eV and 0.059 eV, respectively. The findings also suggest that chloride ion diffusion is facile on hydrated calcium silicate.