EuO Surface Reconstruction

Hello,

I am attempting to calculate the reconstruction on the polar 111 surface of EuO and have a question regarding the setup.

I have been able to calculate the ground state of the surface but am now undergoing the relaxtion of the geometry.

My question is, as the surface layers of either Eu or O ( I am testing both cases) relax, it is my understanding that the local electronic structure will alter for these atoms in relation to the bulk like atoms within the surface model and as such, would it be advisable to catergorize these atoms as a different atom then the bulk. That is to say, would it be advisable to copy the Eu.in species file to a Eu-Surface.in species file so that the linearisation energies of the two would be allowed to be calculated independently? Or would be doing so be unneccesary since the atomic-like orbitals are so low lying that their modification due to the different enviroments be relatively unchanged?

If this question in and of itself is a misunderstanding, could I get some clarification or be pointed in the right direction to clarify myself?

Thank you for any help,

Robert D. Nielsen

mfechner - 2019-05-09

Dear Robert,

I think it is enough to specify Eu several times to get elk into a state treating these atoms as different. Exemplary here a modified version of the NiO LDA+U example, where I split the Ni sites although they access the same "Ni.in" file, they will be treated as individuals by the code.

atoms
3 : nspecies
'Ni.in' : spfname
1 : natoms; atpos, bfcmt below
0.0 0.0 0.0 0.0 0.0 -0.01
'Ni.in' : spfname
1 : natoms; atpos, bfcmt below
0.5 0.5 0.5 0.0 0.0 0.01
'O.in' : spfname
2 : natoms; atpos, bfcmt below
0.25 0.25 0.25 0.0 0.0 0.0
0.75 0.75 0.75 0.0 0.0 0.0

Note that my experience of surface computations with elk is limited. Although, I did some work on perovskites with pseudo potential codes. From this I took you may need a big slab ...... and care about the surface termination, particular in combination with the periodic boundary condition as this could ''bias'' your surface relaxation.

best
Michael