COMSUBS

Sample Input for COMSUBS:
Phase Transition in NaCl to CsCl Structure

At 30 GPa, NaCl undergoes a phase transition to the CsCl structure. In the rocksalt structure, the space-group symmetry is #225 Fm-3m with lattice parameter a=4.84 A. In the CsCl structure, the space-group symmetry is #221 Pm-3m with lattice parameter a=2.98 A.

Details about how COMSUBS (version 1.0) treats this case can be found in Phys. Rev. B 65, 144114-1-12 (2002). Note that version 2.0 contains major revisions of the algorithm and some of the subgroups listed here are different from those listed in the above reference

The input to COMSUBS is shown below. Click on the start button to produce the output.

Input to COMSUBS:

Note that the input parameters above severely restrict the scope of the subgroups listed in the output (and didn't take very much time to run). In actual studies, you would probably allow larger unit cells and larger atomic shuffles.

Let us point out a few features in the output.

  Na, Wyckoff position a,    0.00000   0.00000   0.00000 
  Cl, Wyckoff position b,    0.50000   0.50000   0.50000
COMSUBS identifies the Wyckoff positions of the Na and Cl atoms to be (a) and (b), respectively, in crystal 1 (and similarly in crystal 2). You should always check these lines in the output to be sure that COMSUBS is putting atoms in the positions you want.

Volume/atom in crystal 1 is     14.172
Volume/atom in crystal 2 is     13.232
COMSUBS calculates the volume/atom for the two crystals: 14.172 A/atom in the rocksalt structure and 13.232 A/atom for the CsCl structure. The volume/atom is a little bit smaller in the CsCl since pressure induces the transition to that structure. You should always check these lines in the output to be sure that you entered a physically reasonable structure.

Nearest distance between atoms in crystal 1 is    2.4200
Nearest distance between atoms in crystal 2 is    2.5808
COMSUBS calculates the nearest-neighbor distance in both crystals: 2.4200 A in crystal 1 and 2.5808 A in crystal 2. You should always check these lines in the output to be sure that you entered a physically reasonable structure.