Electronic structure and chemical bonding of α- and β-CeIr2Si2 intermediate valence compounds

► Energy stabilization of (HT) β-CeIr2Si2 versus (LT) α-CeIr2Si2 from DFT methods. ► Concomitant with the change of Ce valence to tetravalent (HT)-enhanced specific heat. ► Equations of states for La, Ce and Th members with CeIr2Si2 resembling tetravalent-Th. ► Chemical bonding shows changes on the {Ir2Si2} intralayer and CeIV-Ir bonds.