Density functional study of α-CrCl2:: Structural, electronic, and magnetic properties

We present first-principles density functional calculations (DFT) on the alpha phase solid state of the transition metal dihalide compound CrCl2. Structural parameters are optimized using local spin density approximation (LSDA) and semilocal generalized gradient approximation (GGA) exchange-correlation functionals. Different magnetic coupling schemes are investigated. In agreement with experiment we find that alpha-CrCl2 forms antiferromagnetically coupled chains that are connected via weaker Cr-Cl bonds. The internal crystal parameters are well described within DFT-GGA. The absorption spectrum near the onset is dominated by spin-allowed transitions between neighboring Cr atoms. Magnetic coupling constants are calculated from symmetry-breaking solutions of the electronic Hamiltonian. Several DFT-based methods are benchmarked with respect to their ability to reproduce the experimental coupling constants. Both LSDA and GGA fail to do so, and the inclusion of exact exchange worsens the results. Introducing a suitable onsite repulsion term yields good agreement with experiment.