I am studying a mineral in particular and I am investigating the D3, and two other functionals which use the IVDW = 11 tag. For all of these functionals when I use VASPKIT to look at the elastic constants I get wild numbers and it says its mechanically unstable. For the three other functionals which I use with no IVDW = 11, it gains decent numbers and says the structure is stable. I am now trying optPBE and DF_cx to see if its a vdw corrections issue or if its an actual IVDW = 11 issue

I am now also retrying with ISYM = 0, but I was wondering if there could be a reason this could be the case? If further information is required I am happy to provide it

Many thanks,
Jess