[DFTB-Plus-User] Forces in dftb+ (supercells and k-point mesh)

[Anshu Gaur]

Dear all,
I am trying to see effect of forces (of different origins such as coulombic, van-der walls, strain etc.) on the properties of a structure. I have relaxed the structure (< 1e-6 Hartree/Bohr) using a sufficiently large k-point mesh. However, if I change the k-point mesh size (smaller) or make a supercell of the original structure, I see large forces in the structure (without changing atomic positions or lattice parameters). Also, I notice that the x-component of forces on atoms is the most affected (while y- and z-components remain unaffected). I have checked this by changing k-mesh in x-, y- and z- and also making supercells in x- and z- directions, the x-component of the forces always shows large values.
Can the calculation of forces at any other k-point mesh be trusted, if the structure is relaxed using a different k-point mesh? or we should always use the same k-point mesh. Also, can we make a supercell and trust the force calculations?

My structure is 2D with vacuum in y- and extended in x- direction (ribbon like structure, continuous in x- and z-).
Regards,
Anshu
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.zfn.uni-bremen.de/pipermail/dftb-plus-user/attachments/20200316/c436d1a5/attachment.htm>