  We use the dynamical mean-field method to calculate the charge density wave
transition temperature of the half-filled Holstein model as function of typical
phonon frequency in the physically relevant adiabatic limit of phonon frequency
Omega much less than electron bandwidth t. Our work is the first systematic
expansion of the charge density wave problem in Omega/t. Quantum phonon effects
are found to suppress Tco severely, in agreement with previous work on one
dimensional models and numerical studies of the dynamical mean field model in
the extreme antiadiabatic limit (Omega ~ t). We suggest that this is why there
are very few CDW systems with mean-field transition temperatures much less than
a typical phonon frequency.
