The effects of disodium malonate, disodium succinate, disodium glutarate, and disodium adipate on the crystal habit of calcium sulfate a-hemihydrate (CaSO(4 center dot)0.5H(2)O, alpha-CSH) were studied using experimental studies and molecular dynamics simulations. The calculation and experimental results provided insight into the mechanism of the interaction between the additives mentioned above and the different faces of alpha-CSH that dominate the morphology of alpha-CSH. The calculation results indicated that the formation of high-aspect-ratio alpha-CSH, namely, calcium sulfate alpha-hemihydrate whiskers (alpha-CSH whiskers), in aqueous solution was due to the interaction between liquid water and side faces of the alpha-CSH crystal, which inhibits the growth of alpha-CSH along the radial direction. However, when a trace amount of crystal habit modifier, such as disodium succinate or disodium glutarate, was added to the aqueous solution, the growth rates along the directions normal to the {001} and {114} faces were considerably inhibited. Thus, alpha-CSH crystals with a low aspect ratio were synthesized using a hydrothermal method. In addition, the calculation methodology used in this work could provide a powerful tool for selecting suitable crystal habit modifiers for preparing alpha-CSH and other inorganic crystals.