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Dear vaspmaster,

I don't understand the following section of code in the subroutine RD_POSCAR_HEAD in poscar.F

73 CALL LATTIC(LATT_CUR)
74
75 IF (LATT_CUR%OMEGA<0) THEN
76 IF (IU0>=0) &
77 WRITE(IU0,*)'ERROR: the triple product of the basis vectors ', &
78 & 'is negative exchange two basis vectors'
79 STOP
80 ENDIF
81

is there a physical reason why the triple product needs to be positive or is this just a convention ?

Thanks !

according to the conventions of crystallography, the lattice vectors have span the lattice according to the right-hand-rule.