INTERMOLECULAR POTENTIAL IN SOLID METHANE. II: COHESIVE ENERGY, CRYSTAL STRUCTURE, AND PHASE TRANSITION,
Abstract
The cohesive energy of crystalline methane is calculated for various possible structures, using a potential function consisting of repulsive and attractive interactions between non-bonded atoms. The necessary parameters were taken without at justment from independent studies of other sys tems. It was found that the structures D sub 2d have the best packing. It is proposed that the lambda-type phase transition in methane at 20.4 K may be associated with a tetragonal distortion of the f.c.c. unit cell with no change in volume, since the calculated cohesive energy of methane is thereby increased. The maximum contribution of this distortion (about 1% of the total energy) occurs when the c-axis of the unit cell is elon gated 12%. This change agrees reasonably well with the experimental heat of transition, 18.1 cal/mole, which is 0.8% of the sublimation energy of methane. The calculated stability of the crystal is not affected by slight displacements of the molecules along the c-axis. On the other hand, the calculated stability of the crystal de creases upon rotation or upon distortions from T sub d symmetry of the individual molecules in the lattice. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1963
- Accession Number
- AD0416001
Entities
People
- A. Ron
- And D.f. Hornig
- S. Kimel
Organizations
- Princeton University