CORRELATION ENTROPY OF THE H-2 MOLECULE

Correlation of a quantum many-body state makes the one-particle densit y matrix nonidempotent. Therefore, the Shannon entropy of the natural occupation numbers measures the correlation strength on the one-partic le level. Here, it is shown how this general idea of a correlation ent ropy must be adapted for two-electron systems in view of conservation laws which mix Slater determinants even in the noninteracting limit. R esults are presented for the correlation entropy s of H-2 as a functio n of the nucleus-nucleus separation X. Ln the ground state, the entrop y of the spatial factor of the wave function maximizes 1.7 bohr beyond the Coulson-Fischer separation. The role of the correlation entropy i n density functional theory is also discussed. (C) 1997 John Wiley & S ons, Inc.