Quantum-mechanical simultion of the Fe-Si(001) system at the growth stage of a solid wetting layer

Within the framework of density functional theory and the pseudo-potential method, the atomic and electronic structures of the film-substrate system at 0 K in the state of minimum free energy were studied during step-by-step (with a step size of one atomic diameter of Fe) deposition of a Solid Wetting Layer (SWL) Fe up to a thickness of 8 monolayers (ML) onto a normal Si(001) lattice compressed by 1.33 times in the $\langle$011$\rangle$ direction. It is shown that SWL grows in three stages: first, 2$D$, i.e. SWL with compositions Fe$_2$Si and FeSi is formed on a normal and, accordingly, compressed substrate, and then 2$D$-SWL Fe and 3$D$-SWL Fe are sequentially formed. During the growth process of SWL, a three-dimensional environment of Fe atoms is built and the degree of coordination of Fe atoms, with a Fe thickness of 6.4 ML, reaches 10. As a result of this, an electronic structure specific of the bulk phase (BP) Fe is formed. After which, at a thickness of 8 ML Fe, a metastable and stable BP Fe is formed with an bc monoclinic lattice and, accordingly, bcc, i.e. lattice on a normal and compressed substrate. This process is accompanied by compaction of adjacent layers of the Si substrate and their transformation into high-pressure phases.