Electron correlation described by extended geminal models: The EXGEM7 and EXRHF3 models

Within the framework of the general extended geminal model, two new approximate models, EXGEM 7 and EXRHF 3, are introduced. Compared with previous models, these new models imply a more sophisticated approximation of the four-electron terms {?_KL}. The models are tested by calculations on the beryllium atom and the HF molecule.