Thankyou very much for the suggestions. I tried both, but didn't get the structure I was hoping to get. Second one seemed simpler. About the second option, where I generate two bulk slabs, one for Fe and one for MgO, I have some questions.
1. I first generated the Fe struct input, then used the supercell program to introduce vacuum towards the bottom of the Fe slab. In this, for simplicity I used 3 cells along only z-direction, and the vacuum needs to be introduced after the third one (bottommost). I want to attach the MgO slab in the vacuum. You had written that the vaccuum needs to be big enough to accommodate the MgO slab. I do not know how to control *from* which point *to* which point the vaccuum is needed. In other words I imagine that I want all Fe atoms arranged till some value of 'z' and the rest of the cell should be vaccuum, of same size as MgO whcih I will attach later. But whatever I use for the magnitude of vaccuum (only along z), it is pushed towards the end of the slab and vaccuum is introduced only in the last layer ! I dont know what mistake I am doing. Could you tell me what is the 'repeat atoms' for and what is the problem in the abov eprocedure ? Also, I am facing a problem in shifting the atoms. Since my entire Fe slab is ~ 8 Angstroms along z, with (0,0,0) at the top of the slab, I want to shift the MgO slab by this amount. I use the optional shift. If the lattice constant of MgO ~ 4.12 Angstroms, then whatever shift I input as fractional coordinates, the MgO block is getting cut. I thought I am shifting the origin along the Z-axis, but that doesnt seem to be happening. Eagerly waiting for your response, Best, Krish