Repulsive Potential and Their Multi-Body Expansion of Compressed Atomic Cluster Hen (n＝3, 4, 5)

Lowdin scheme is applied to calculate the repulsive potentials and their multi-body expansion of compressed atomic clusters Hen (n＝3, 4, 5). It is found that the multi-body expansion converges more slowly as the members of atoms and compression increase. In multi-body expansion, the two-body and four-body contributions are repulsive and the three-body and five-body contributions are attractive. Therefore, when we treat many-body interaction by means of multibody expansion approach, the two-body approximation always overestimates repulsive potentials and three-body corrections soften system too much. These results agree with the new experiments. It is also found that the four-body and five-body contributions are important for the equation of state of dense helium.