Quantum mechanical geometry optimizations and molecular dynamics simulations were performed of trichloroethene (TCE) adsorbed on the mineral surfaces in the interlayer space of an idealized nontronite, a 2:1 clay mineral containing structural Fe2+. Density functional procedures were used as implemented in the ab initio program CASTEP, in fully periodic calculations. Geometry optimization included the atomic positions of the mineral and the adsorbates within the unit cell, in addition to unit cell lengths and angles, achieving full optimization of the entire crystal system. In the absence of water, TCE molecules reside flat on the mineral basal planes and the molecular structure is not significantly different from that of the isolated system. In the presence of water, geometry optimization leads to a nonplanar structure, with the cis-Cl-C=C-Cl torsion at 52.5degrees and a C...Cl distance of similar to3 Angstrom. The molecular dynamics simulations show that the elongated C...Cl distance has lost the oscillatory proper-ties of a true bond, which are clearly observed for the other bond distances of TCE, with frequencies of the right order of magnitude. The crystal lattice of the optimized nontronite with TCE and water in the interlayer space shows the structural features of oxidized nontronite, even though the starting structure was that of the reduced nontronite. The results make it promising to test the possibilities of joint computational and experimental techniques in finding the best conditions under which catalytic processes on clay mineral surfaces will occur.