symmetry and isif

[IBRAHIM]

Hi,

For relaxation of cell shape and volume using ISIF=3 and relaxation of cell shape using ISIF=4, so a change in Bravais lattice is allowed. 

With ISYM=2, ISIF=3 or 4 also changes the Bravais lattice and the lattice angles and vectors are changed for some of my systems. What happened in this case, is the symmetry analysis and quantity summarization (total charge density, force, stress tensor) done according to the determined space group at each ionic step?

When I checked the forum, it was stated that the symmetry will be constrained and will not be lowered if the change of cell shape is allowed and ISYM=2.

https://www.vasp.at/forum/viewtopic.php ... +%3D2#p747
https://www.vasp.at/forum/viewtopic.php ... etry#p1454

Thanks 

[pedro_melo]

Dear IBRAHIM,

Both ISIF= 3 or 4 allow for change in cell shape. ISYM=2 calls a more efficient algorithm to explore the symmetries of the cell, but I do not think it will force the preservation of the initial symmetry group that you provide in the input file. Could you try with a different choice of ISIF (please see https://www.vasp.at/wiki/index.php/ISIF) that does not allow for changes in the cell shape?

If that does not work, please provide us with your input files (POTCAR, POSCAR, INCAR, KPOINTS) so that we can study the issue.

Kind regards,
Pedro Melo