Lattice parameters of mp-24610.

The lattice parameters of LiP(HO2)2 crystal with space group Pna21 were calculated as: a=6.394, b=6.926, c=7.702. The experimental values of lattice parameters by x-ray diffraction [M. Catti and G. Ivaldi, Z. Kristallogr. 146, 215 (1977)] were obtained as: a=6.253, b=7.656, c=6.881, while those by neutron diffraction [Oh et al., J. Phys. Soc. Jpn. 79, 074606 (2010)] were measured as: a=6.241, b=7.643, c=6.870. In addition, neutron diffraction could determine the hydrogen position. For comparison of the calculated fractional coordinates of each atom with the experimentan values, the b and c axis in the calculation should be interchanged. Such a work can play the role of interpretation of the vibrational spectra of LiP(HO2)2 crystal.

Hi @KwangseiLee, welcome to the forum!

The differences between calculated and experimental parameters (e.g. 6.394 Å vs 6.253 Å) are within the accuracy expected for this level of theory.

For comparison of the calculated fractional coordinates of each atom with the experimentan values, the b and c axis in the calculation should be interchanged.

The reason the *b* and *c* parameters are swapped is because of a change in setting. Note that in an orthorhombic crystal system there is not a unique choice of axes; one choice is not “correct” or “incorrect” but is decided by convention.

We report the space group as Pna2_1 by convention. For this space group we have multiple settings available:

ITA number | Setting | \mathbf{P} | \mathbf{P}^{-1} |
---|---|---|---|

33 | P n a 2_1 | a,b,c | a,b,c |

33 | P b n 2_1 | b,a,-c | b,a,-c |

33 | P 2_1 n b | c,a,b | b,c,a |

33 | P 2_1 c n | -c,b,a | c,b,-a |

33 | P c 2_1 n | b,c,a | c,a,b |

33 | P n 2_1 a | a,-c,b | a,c,-b |

Information courtesy of the Bilbao crystallographic server, where \mathbf{P} is the transformation to the conventional ITA setting via (a, b, c)_n = (a, b, c)_s \mathbf{P}. More information on the ITA settings can be found here.

To compare with experiment, it is often necessary to make sure both reference crystal structures are in the same setting, but it is outside the scope of Materials Project for us to do that.

Hope this helps,

Matt