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If one phase exhibits PO, a simple statement is necessary:
GEWICHT=SPHARx
x
determines the order of the spherical harmonics model and can
be 0, 2, 4, 6, 8 or 10. Except the triclinic lattice there are constraints
between the parameters of the model. BGMN itself determines these constraints
automatically.
Lets have a look at the gypsum structure file, lines 5 and 6:
PHASE=Gypsum SpacegroupNo=15 HermannMauguin=I12/a1 // PARAM=A=0.6522_0.645^0.658 PARAM=B=1.5202_1.51^1.53 // PARAM=C=0.5679_0.56^0.575 PARAM=BETA=118.4_118^119 // RP=3 PARAM=B1=0_0^0.008 // GEWICHT=SPHAR6 GOAL:gypsum=GEWICHT E=CA+2 Wyckoff=e TDS=0.0088 y=0.4213 E=S Wyckoff=e TDS=0.0066 y=0.9216 E=O-2 Wyckoff=f TDS=0.0149 x=0.5505 y=0.1319 z=0.9632 E=O-2 Wyckoff=f TDS=0.0141 x=0.6671 y=0.0223 z=0.7582 E=O-2 Wyckoff=f TDS=0.0219 x=0.4588 y=0.1821 z=0.3796There is the
GEWICHT=SPHAR6
statement in line 5 which determines
the use of a 6th order spherical harmonics model.
If the phase content is too low, the order of the model will be reduced down
to SPHAR4
, SPHAR2
or even SPHAR0
(isotropy), if necessary. Thats why you can use the same structure file for all
analytical problems even if nearly nothing of the phase is contained in the
sample.