position of atoms in unit cell and structural relaxation

[hongbiao]

For structural relaxation (ISIF=3) for the unit cell, there are two different ways in terms of the initial positions of atoms in the unit cell: atoms on the high symmetry points, and atoms on the positions slightly adjusted from the high symmetry positions. For the two cases, the relaxed structure and total energy are a little bit different with each other. As the very important step for subsequent calculations, I am wondering which method is more reasonable, or depends? Which parameter should be used to judge the reasonability? Thank you for your help.

[admin]

You are right with two ways in terms of the initial positions of atoms.
May be the question should be asked in a different way.
Is it necessary to allow the variation of the cell shape when
the symmetry of the structure is well known (from XRD analysis)?

[hongbiao]

Yeah, should. Thank you.

[hongbiao]

I have a related question: when you check my another question about structural relaxation, you will find that all the forces in the y direction
are 0, while forces in the x and z directions are too big and not converged. Is this case has something to do with the symmetry? Thank you.