I have problem when I refined the fraction site occupancy for 3 atoms, Fe, Co and Ti. The result shows negative occupancy for nonsense numbers. What I did , added constrain

Fe1+Co1+Ti1=1

Fe2+Co2+Ti2=1

Fe3+Co3+Ti3=1

Fe4+Co4+Ti4=1

Fe5+Co5+Ti5=1

Also I tried to set upper and lower limit , calculate >> view LS parm >> phase >> fractions add min value=0 and max value=1. then refine, I still have negative value for some sites example for

Fe1=-1.2626

Co1= -1.59095

Ti1= 3.7721

any trick to force the refine the value to be in range of limit ??

Thanks