  In a recent paper [arXiv:0804.3569], Takatoshi Nomura {\it et al.} reported a
structural phase transition near 150 K in LaOFeAs and used space group "Cmma"
to describe their X-ray diffraction data. However, they did not discuss how
their proposed structure compares with the early neutron study by Cruz {\it et
al.}[arXiv:0804.0795] where the low temperature structure of LaOFeAs was
described by space group "P112/n". This caused some confusion, suggesting that
there may be some disagreement on the low temperature structure of LaOFeAs as
evidenced by several inquiries that we received. Here we show that the proposed
structures from x-ray and neutron diffraction are basically identical. The P2/c
(i.e., P112/n) cell becomes the primitive cell of the Cmma cell when the
z-coordinate of the oxygen and iron are assumed to be exactly 0 and 0.5 (these
numbers were reported to be -0.0057 and 0.5006 in neutron study). Our
first-principles total-energy calculations suggest that the oxygen and iron
atoms prefer to lie on the z=0 and 1/2 plane, respectively, supporting Cmma
symmetry. However it is more convenient to describe the structural distortion
in the primitive P2/c cell which makes it easier to see the connection between
the high (i.e., P4/nmm) and low temperature structures.

Superconductivity;Materials Science