  Electronic decoherence processes in molecules and materials are usually
thought and modeled via schemes for the system-bath evolution in which the bath
is treated either implicitly or approximately. Here we present computations of
the electronic decoherence dynamics of a model many-body molecular system
described by the Su-Schreefer-Heeger Hamiltonian with Hubbard electron-electron
interactions using an exact method in which both electronic and nuclear degrees
of freedom are taken into account explicitly and fully quantum mechanically. To
represent the electron-nuclear Hamiltonian in matrix form and propagate the
dynamics, the computations employ a Jordan-Wigner transformation for the
fermionic creation/annihilation operators and the discrete variable
representation for the nuclear operators. The simulations offer a standard for
electronic decoherence that can be used to test approximations. They also
provide a useful platform to answer fundamental questions about electronic
decoherence that cannot be addressed through approximate or implicit schemes.
