  New representation for the generating function of correlators of third
components of spins in the XX Heisenberg spin chain is considered in the form
given by the fermionic Gaussian path integrals. A part of the discrete
anti-commuting integration variables is subjected to ``automorphic'' boundary
conditions in respect of imaginary time. The situation when only a part of the
integration variables is subjected to the unusual boundary conditions
generalizes more conventional ones when ``automorphic'' boundary conditions
appear for all sites in the lattice spin models. The results of the functional
integration are expressed as determinants of the matrix operators. The
generating function, as well as the partition function of the model, are
calculated by means of zeta-regularization. Certain correlation functions at
nonzero temperature are obtained explicitly.
