QUANTUM SIMULATIONS IN MATERIALS SCIENCE: MOLECULAR MONOLAYERS AND CRYSTALS

The properties of adsorbed molecular layers and molecular solids are reviewed in this paper. Phase transitions and time-dependent properties of pure and mixed molecular crystals are analyzed. Phase transitions in adsorbed (2D) fluids and in adsorbed layers of molecules are studied with a combination of path integral Monte Carlo (PIMC), Gibbs ensemble Monte Carlo (GEMC) and finite size scaling techniques. Entropy driven phase transitions in systems with purely repulsive interactions are analyzed as well phase diagrams of fluids with internal quantum states. Adsorbed layers of H₂ molecules at a full monolayer coverage in the structure have a higher transition temperature to the disordered phase compared to the system with the heavier D₂ molecules, this effect is analyzed by PIMC. Linear N₂ molecules adsorbed on graphite show a transition from a high-temperature phase to a low-temperature phase with herringbone ordering of the orientational degrees of freedom, the order of the transition and quantum effects are discussed. Rounding effects of the phase transition in adsorbed layers of (N₂)_x (CO)_1−x for x < 7% are analyzed.