  Recently Wang et al. [Phys. Rev. Lett. 104, 027801 (2010)] discovered a new
polar smectic phase with six-layer period (SmC*d6). In this manuscript, we
demonstrate that the theory [Phys. Rev. E 67, 041716 (2003)] based on the free
energy expansion with a two-component order parameter predicted the six-layer
phase, describes its structure and the phase sequence observed in experiment
[Phys. Rev. Lett. 104, 027801 (2010)].
