Figure 4

Total energy DFT + U calculations performed on CoCl₂ (space group P\(\overline{3}\) m1) using a Coulomb correlation energy, U = 3 eV. Top panels show the electron DOS projected on the Co²⁺ 3d (blue) and Cl⁻ 3p (red) orbitals at 23 (HS), 67 (LS), 153 (met) and 214 (deloc) GPa (a–d). The corresponding spin density around the Fermi level on the (111) plane is shown in panels below with red and blue denoting up and down spin density. A schematic Co²⁺ 3d bands associated with t_2g (e_e′, a_1g) + e_g in blue and red colors, respectively, illustrates the HS and LS states (e,f). It must be noted that spin density in LS is significantly localized around Co²⁺ whereas it is more delocalized around Cl⁻ in spite the electronic Fermi levels have about the same contributions from Cl⁻-p and Co²⁺-d orbitals (detailed information in Supplementary Figs S7–S10). Note that above 150 GPa, calculated pressures by DFT + U are overestimated as the Coulomb correlation energy was fixed to U = 3 eV. Indeed pressure should be corrected by about 20% in that range if U decreases by 20% due to ultra-high pressure effects. The lattice structure of CoCl₂ is depicted in (g). Note that the green plane is (111) plane for spin density plot.