New variational function in the theory of quasi-one-dimensional metals

Variation function of a new type is proposed for the one-dimensional crystals with partially filled conduction band. The function used can not be represented in terms of the product of the fermi operators. The approach developed is applied to the one-dimensional Hubbard model with the repulsion and attraction between the electrons. It is shown that the new function gives lower value for the ground state energy than such well-known methods as the generalised Hatrtee–Fock or spin density wave method, the Bardeen–Cooper–Schrieffer method, the charge density wave method and makes it possible to consider the current as well as neutral excitations.