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[ricinski@semi.ee.es.osaka-u.ac.jp]

For PbTio3 the result is reasonable and there are no problems with this 
material that has been often calculated. It may be OK for BiScO3 too, but to 
be sure you should probably change the ionic coordinates in small steps from 
the centrosymmetric structure to the ferroelectric structure. In some 
materials the berry phase may span the (-1, 1) interval more than once, as I 
recall it happened for me when making BiFeO3 calculations. You should also 
investigate if the crystal always remains insulating along the ionic 
displacements path...

Good luck!

Dan Ricinschi