In Figure we report various in-situ electronegativities of calcium, 𝜒̅ 𝐶𝑎 𝑣𝑎𝑙 , as: 1) isolated atom, both in gasphase (which in our nomenclature corresponding to 𝜒̅ 𝐶𝑎 0 , see Computation Details) and under pressure (these values are tabulated in ) and 2) atom in a crystalline material for the fcc, bcc and sc (Ca-I, -II and -III respectively) phases in the pressure range from 0 to 40 GPa. , is labelled as "Atom", while the electronegativity of an isolated atom under pressure is marked by the red line. Our calculated In-situ electronegativities in the fcc, bcc and sc crystalline phases for calcium, up to 40 GPa, are reported as bluecircles, green-squares and pink-triangles respectively.