Relaxed crystalline and icosahedral molecular clusters: CO2
Abstract
To obtain structural models for gas-phase molecular clusters of CO2, multishell cubo-octahedral fcc crystal fragments, consisting of up to five concentric shells (561 molecules) were allowed to relax, assuming -12-6-1 pairwise additive nonbonded atom-atom interactions. The resulting icosahedral deformation is most pronounced in the outer shells, whereas the inner shells remain nearly crystalline; the deformation decreases with growing cluster size. The relaxed crystalline clusters (except the one-shell cluster) do not correspond to global minima in the potential-energy surface, however. More favorable structures exist, consisting of nested, nearly undistorted icosahedra, analogous to the Mackay arrangements of equal spheres, suggesting that such arrangements are not only energetically favorable for aggregates of spherical inert-gas atoms, but also for assemblies of nonspherical molecules, with highly anisotropic interactions, including electrostatic. The relative energy difference between relaxed crystalline and icosahedral clusters of the same size ranges from 2.4% (two shells) to 0.8% (five shells). The available experimental evidence suggests bulk-crystalline structure in the N=100 range.
- Publication:
-
Journal of Chemical Physics
- Pub Date:
- May 1987
- DOI:
- 10.1063/1.452543
- Bibcode:
- 1987JChPh..86.5660V
- Keywords:
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- Carbon Dioxide;
- Crystal Structure;
- Icosahedrons;
- Molecular Relaxation;
- Molecular Structure;
- Face Centered Cubic Lattices;
- Polyatomic Molecules;
- Atomic and Molecular Physics