Dear Users/Developers,

I encontered a situation that the elastic constant C14 from MS/CASTEP is negative, I am not knowledge enough to know if this is because of the alternative axis selection like what happened to Al2O3 in the literature, or it is calculated following the stadard choice of axis/alignment ( as stated in APPLIED PHYSICS LETTERS VOLUME,  85, NUMBER 3 19 JULY 2004, "Prior to 1952, two alignments (referred to as obverse and reverse) were in use for trigonal crystals, and these gave different signs for one of the elastic constants). Any comment/advise will be appreciated.

Leo