Is it possible for fractional coordinates to have -ve values? If possible please give some reference.
yes, why not? it is could be convenient to use negative coordiantes to have a better visualisation of the asymmetric unit. Just remap them into the conventional cell (just add 1 to them, i.e. a unit cell translation) if you don't like the idea
yes, why not? it is could be convenient to use negative coordiantes to have a better visualisation of the asymmetric unit. Just remap them into the conventional cell (just add 1 to them, i.e. a unit cell translation) if you don't like the idea
Actually after refinement some fractional coordinates were found to be -ve and some were +ve. (i.g. compound-ABC; Ax=+ve, Ay=-ve, Az=+ve; Bx=-ve, By=-ve, Bz=+ve; Cx=-ve, Cy=+ve, Cz=-ve and all are
Try plotting the coordinates you've obtained using some crystallographic software like VESTA or CrystalMaker, and see if you get a crystal that looks sensible! If you're satisfied that the atomic positions are not unreasonable, you can bring everything into the same unit cell by adding 1 to any negative coordinate, as Matteo suggests.
Alternatively, try to find a translation that gives you a more conventional looking unit cell. Without knowing anything about the symmetry of your material I can't say very much, but try putting one of your atoms at the origin. Alternatively, look for similar structures (use one of the online crystallographic databases available) and see if you can get some hints.
@Saswati.. as I said, add 1 (the unity) to the negative values and see if you get the same result... should not be that difficult, right? If you are not convinced about your structure, try getting some bond distances and angles that could help you understnading wht's going on.
@Venkat: I would not suggest randomly to use a software like spuds that is developed for a specific class of materials (and also there it must be used really carefully), without knowing what material she's working with!
You asked for a reference. Here it goes. In Table 1 of the attached paper there are several negative values for fractional coordinates. There is no problem with it at all. To know the corresponding positive value, just add 1 to it.
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