I clarified discrepancies found between the applications to $A15\mathrm{}$ structure of the chain criterion and the Landau theory of second-order phase transitions. I also present complete determination via the chain criterion of all allowed low-symmetry groups based on $X$- and $R$-point representations for $A15\mathrm{}$ ($O_h^3$) structure.

• Received 27 February 1980

DOI:https://doi.org/10.1103/PhysRevB.25.2015