Simulations of methylthiolate using both classical molecular dynamics with Amber14SB and CHARMM36m, as well as ab initio molecular dynamics, revealed substantially different hydration structures (Figure ). Specifically, Amber14SB methylthiolate exhibited a radial distribution function (RDF) peak backshift of 0.5 nm compared to AIMD, suggesting a potentially erroneous hydration structure (Figure ). This observation is consistent with previous work employing different AIMD schemes and simulation setups. Given the significant discrepancy in prediction performance between CHARMM36m and Am-10 ber14SB, as well as the notable differences in RDFs, we rescaled the Lennard-Jones σ value to improve agreement with the AIMD RDF and potentially improve pK a prediction performance.