Realistic models of hydroxylated amorphous silica surface and MCM-41 mesoporous material simulated by large-scale periodic Lee-Yang-Parr (B3LYP) calculations, was reported. All the proposed models envisage silanol-terminated surfaces, and are simulated using a full ab initio Becke three-parameter B3LYP periodic treatment, based on the massive parallel version of CRYSTAL06 code. The model consisted of a very reasonable starting point for ab initio modeling of adsorption processes occurring either at amorphous silica surfaces or within the pores of the MCM-41 material. Models for amorphous surfaces were built starting from a classical molecular dynamics simulation of bulk cristobalite heated at very high temperatures and properly annealed. The annealing process was carefully scheduled to avoid introducing and exceedingly large number of structural defects in the final structure. Analysis of the structure reveals that the MCM-41 model has a 7.2 OH nm-2 density, and only 33 silanols are not involved in H-bonds.