R1Q8 Unit cell angles

[dagewa]

What were the alpha, beta, gamma of the unit cell found? The lengths of the vectors are usually more affected by the systematic error – the effective camera length (the effective distance to the detector), whereas the angles are affected by the scattering of the data.

[dagewa]

The initial indexing solutions for each case are triclinic, so the cell angles do deviate from 90 degrees. However, this is a poorer model for the crystal than the model produced after refinement. At this stage, lattice symmetry constraints have been applied, and smooth unit cell, orientation and beam drifts have been refined. The most relevant information about the quality of the model are the RMSDs after refinement. If these are low even when cell angles are constrained by lattice symmetry (as is the case here, see Table 1) then the model for the dataset is good enough for accurate prediction of peaks not identified by the spot finding procedure.

[dagewa]

The issue here may be that it is not clear enough in the text of section 2.5 that orthorhombic lattice constraints were applied after indexing. TODO: add sentence to the text to make that clear

[dagewa]

Reply: While the initial indexing solutions for each case are triclinic, orthorhombic lattice constraints were applied immediately afterwards before more sophisticated geometry refinement. Thus, the alpha, beta and gamma angles were enforced to be right angles. Section 2.5 has now been modified to make this fact clearer. The most relevant information about the quality of the model are the RMSDs after refinement, including smooth unit cell, orientation and beam drift modelling (shown in Table 1). This type of refinement was not attempted with the triclinic solution. The fact that the refined model gives low RMSDs even when cell angles are constrained by lattice symmetry indicates that the model for the dataset is good enough for accurate prediction of peaks not identified by the spot finding procedure.