Ab Initio vs Literature Stiffness Values for Ga: A Caveat About Crystal Settings
Yvon Le Page, Paul Saxe
Physica B: Physics of Condensed Matter 307, 191 (2001)
The structure of orthorhombic gallium was ﬁrst determined in 1933 in the space group Cmca. The recent crystal structure literature also consistently uses this setting. The ab initio stiﬀness coeﬃcients calculated from this crystal structure are: C₁₁=88, C₁₂=29, C₁₃=34, C₂₂=116, C₂₃=24, C₃₃=98, C₄₄=37, C₅₅=38, C₆₆=27 GPa. Comparison with experimental stiﬀness literature values averaged from three studies, followed by an extended search of the literature showed that the Abma setting was used in all three independent experiments but not clearly reported. This ﬁnding stresses the need for proper reporting of the Cartesian system for both computed and measured properties. Printing the cell data, space-group name, fractional atomic coordinates for independent atoms and a reference to the set of rules used to ﬁx the Cartesian axes constitutes suﬃcient information to ﬁx the crystal and its setting in the Cartesian axes for all symmetries and for all properties.