Accurate long-range coefficients for two excited like isotope He atoms: He($2^{1}P$)--He($2^{1}P$), He($2^{1}P$)--He($2^{3}P$), and He($2^{3}P$)--He($2^{3}P$)

J. -Y. Zhang, Z. -C. Yan, D. Vrinceanu +2

A general formalism is used to express the long-range potential energies in inverse powers of the separation distance between two like atomic or molecular systems with $P$ symmetri…