[Pw_forum] A question about relaxing interfaces

[Hongbin Zhang]

Dear all PWSCF users,

I am trying to do some relaxation calc. of interfaces with PWSCF, but
these's a question wrt relaxations:

Suppose we have a supercell without vacuum layers and only one
interface (i.f.), which might look like this:

        -------
        |     |
        |bulk1|
        |     |
        | i.f.|
        |     |
        |bulk2|
        |     |
        ------
There are strong inplane constraints, so we only relax distances between
atomic layers at the interface. So here comes my problem: if we use
"relax", the atomic layers at the interface will be relaxed, but since the
whole z lattice constant won't change, the structure is supposed to be not
fully relaxed. Is this right?

Otherwise, if we use "vcrelax", how could one set up inplane constraints?

Thanks a lot.

Bests