Molecular mechanics and molecular dynamics simulations have been used to predict the mechanical properties of amorphous polystyrene as a function of the chain tacticity. Relaxed and equilibrated microstructures were generated and the cohesive energy density and the solubility parameter calculated. The amorphous state disorder was analyzed in terms of the pair correlation functions and the Voronoi polyhedra. Two separate methods, the static structure deformation and the stepwise loading molecular dynamics were used to apply small strain deformations to generated microstructures to obtain the elastic constants. The resulting values for moduli are compared, and the performance of the methods is discussed.