# Help understanding and reading atomic positions of crystals

I am familiar with both Cartesian coordinates and fractional coordinates of crystals. However, I am having trouble reading the atomic positions that are listed in some research papers. For example, for orthorhombic CaTiO3 the atomic positions are listed as:

    Atom #      OX   SITE   X            Y            Z         SOF   H
Ca   1         2.0    4c   -0.00676(7)   0.03602(6)   0.25       1.   0
Ti   1         4.0    4b    0            0.5          0          1.   0
O    1        -2.0    4c    0.0714(3)    0.4838(2)    0.25       1.   0
O    2        -2.0    8d    0.7108(2)    0.2888(2)    0.0371(2)  1.   0


I assume that they are in Cartesian coordinates since they are labelled x, y, and z. However, when I use the coordinates to construct a unit cell, the atoms overlap.

In the drawing, red=oxygen, yellow=ca, gray=titanium. They are all bunched up at the origin (0,0,0). Furthermore, repeating the unit cell (such that it forms a lattice) does not yield me a correct structure. I also tried fractional coordinates, just to be sure. However, I obtain erroneous results. I think I am misunderstanding what these coordinates represents or how they are read. What am I doing wrong? Also why are there only 2 oxygens when the formula is CaTiO3? Any help would be appreciated

• could you perhaps post the reference? – bremsstrahlung Mar 7 '16 at 6:55
• icsd.kisti.re.kr/icsd/… – CoffeeIsLife Mar 7 '16 at 7:03
• the drawing I did it myself using Gaussview – CoffeeIsLife Mar 7 '16 at 7:04
• You would need to apply the appropriate symmetry operations to those points (using the 'site' type). It's ridiculously convoluted. You're best to look elsewhere (specifically, page 80-81 here). – lemon Mar 7 '16 at 9:57
• – CoffeeIsLife Mar 7 '16 at 11:30