Report-no:  FM 98-14;

Authors: G. Benfatto, G. Gentile, V. Mastropietro.

Title: Peierls instability for the Holstein model with
rational density.

Abstract: We consider the static Holstein model,
describing a chain of Fermions interacting with a
classical phonon field, when the interaction is weak and
the density is a rational number rho=P/Q, with P,Q
relative prime integers.  We show that the energy of the
system, as a function of the phonon field, has one (if Q
is even) or two (if Q is odd) stationary points, defined
up to a lattice translation, which are local minima in the
space of fields periodic with period equal to the inverse
of the density.

Key Words: Fermi systems, Peierls instability.

G.Be.: Matematica, Universita' di Roma 2, Viale Ricerca 
       Scientifica, 00133, Roma, Italy.
G.Ge.: Matematica, Largo S. Murialdo, Universita' di Roma 3,
V.Ma.: Matematica, Universita' di Roma 2, Viale Ricerca 
       Scientifica, 00133, Roma, Italy.
e-mail benfatto@mat.uniroma2.it
       gentile@ipparco.roma1.infn.it
       vieri@ipparco.roma1.infn.it