Many-body experts like to start from the one-particle approximation. Even when geminals or group functions are used they are ultimately expanded in the one-particle basis (Wilson 1984). Computational difficulties with the explicitly correlated wavefunctions prevented the use of these methods for all but a few-electron systems (Handy 1978), although there are still some, who have not buried all their hopes, and whose results are promising (cf Jankowski and Malinowski 1980; Jeziorski et al 1984). Notwithstanding their hopes the majority votes for one-particle approximation, because it is fundamental to our intuitions and capable of high accuracy (cf Handy 1978).
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