Atomistic Insight into N‐A‐S‐H and K‐A‐S‐H Gel Formation and Carbonation‐Related Energetic Response

Abstract

Sodium or potassium aluminosilicate hydrate gels, namely N‐A‐S‐H and K‐A‐S‐H, are the main reaction products of low‐calcium geopolymers, and the effect of alkali cations on their local structure and carbonation‐related energetic response needs further clarification. This study combines experimental synthesis, reactive molecular dynamics and DFT‐SCF calculations to compare N‐A‐S‐H and K‐A‐S‐H gels. Ternary analysis confirmed the consistency between simulated and synthesized gels. Reactive molecular dynamics showed polymerization from Q ^o to Q ² ‐Q ⁴ species in both systems, while RDF analysis revealed different alkali‐O environments. K ⁺ exhibited broader and less localized oxygen coordination than Na ⁺ . DFT‐SCF results showed that K‐A‐S‐H interacted more favorably with HCO ₃ ^– /H ⁺ species than independently constructed N‐A‐S‐H. Replacing K with Na in the K‐A‐S‐H framework under the same atom number and framework configuration gave a slightly more negative energy change, suggesting that the carbonation‐related energetic response depends on both alkali type and local framework configuration.