  Pariser-Parr-Pople (P-P-P) model Hamiltonian is employed frequently to study
the electronic structure and optical properties of $\pi$-conjugated systems. In
this paper we describe a Fortran 90 computer program which uses the P-P-P model
Hamiltonian to solve the Hartree-Fock (HF) equation for infinitely long,
one-dimensional, periodic, $\pi$-electron systems. The code is capable of
computing the band structure, as also the linear optical absorption spectrum,
by using the tight-binding (TB) and the HF methods. Furthermore, using our
program the user can solve the HF equation in the presence of a finite external
electric field, thereby, allowing the simulation of gated systems. We apply our
code to compute various properties of polymers such as $trans$-polyacetylene
($t$-PA), poly-\emph{para}-phenylene (PPP), and armchair and zigzag graphene
nanoribbons, in the infinite length limit.
