Calculation of the stability of nonperiodic solids using classical force fields and the method of increments: N2O as an example.

Combining classical force fields for the Hartree-Fock (HF) part and the method of increments for post-HF contributions, we calculate the cohesive energy of the ordered and randomly disordered nitrous oxide (N2 O) solid. At 0 K, ordered N2 O is most favorable with a cohesive energy of -27.7 kJ/mol. At temperatures above 60 K, more disordered structures become compatible and a phase transition to completely disordered N2 O is predicted. Comparison with experiment in literature suggests that experimentally prepared N2 O crystals are mainly disordered due to a prohibitively high activation energy of ordering processes.