The half-filled extended Hubbard model (including nearest-neighbor int
eraction) is considered in perturbation theory at weak coupling on a d
-dimensional hypercubic lattice (d greater than or similar to 3). It i
s shown that the exact critical temperature and the exact order parame
ter in the weak-coupling limit differ from the corresponding Hartree r
esults by a renormalization factor q of order unity. This renormalizat
ion factor q is calculated systematically up to O(1/d) in a 1/d expans
ion. The results depend sensitively on dimension and on the relative s
trength of the nearest-neighbor interaction. The renormalization facto
r in d = 3, estimated from the 1/d expansion, is q similar or equal to
0.282 for the pure Hubbard model, q similar or equal to 0.179 near th
e spin-density-wave to charge-density-wave transition and q similar or
equal to 0.830 in the limit of pure nearest-neighbor interaction.