Ab initio study of molecular chromium-based ring based on SIESTA

Finite size nanoscopic systems are very interesting for being halfway between atoms and bulk systems. In this category molecular magnets play very important role in fundamental physics since these systems have shown new magnetic and electronic futures and revealed to be promising for possible applications in quantum computing and magnetoelectronics. Among these systems, there are homonuclear antiferromagnetic ring-shaped molecules formed by transition metal ions in an almost planar ring. Based on first principles density functional theory (DFT) calculations, as implemented in the SIESTA [1, 2] package, we investigate the electronic and magnetic properties of Cr8F8Piv16 molecular ring (in short Cr8). In the first step we study properties of linear model for Cr8 recently proposed in [3]. In this part the main effort was put for finding SIESTA parameters which leads to good agreement of our calculations with other results from literature. We compare the value of exchange interaction parameter J and total energy for different basis sizes and mesh parameters. To be more specific, in this case we study multiple-ζ basis up to TZTP (triple-zeta triplepolarized). In the next step we use two DFT exchange-correlation potential: the local density approximation (LDA) and the generalized gradient approximation (GGA) to investigate properties of Cr8 ring approximated [4] by replacing the pivallic group by H atoms (hydrogen saturation, see in fig. 1). In this part we widely examine the electronic and magnetic properties of Cr8. The total, local and orbital projected density of states are presented. Electron density, deformation density and spin density maps are investigated. Magnetic properties are studied in detail magnetic moments are calculated using different approaches. Different magnetic configurations with randomly distributed spins up and down are considered to extract exchange interaction parameter J in terms of Heisenberg Hamiltonian.