Many-body forces and stability of the alkaline-earth tetramers

► The alkaline-earths trimers and tetramers are stabilized by the three-body forces. ► Two- and four-body forces are repulsive for trimers and tetramers. ► The attractive contribution to the three-body forces has a three-atom electron exchange origin. ► The population of the np-orbitals leads to the sp-hybridization providing the covalent bonding.