  We consider a Bose-Einstein condensate of polar molecules in a harmonic trap,
where the effective dipole may be tuned by an external field. We demonstrate
that taking into account the dependence of the scattering length on the dipole
moment is essential to reproducing the correct energies and for predicting the
stability of the condensate. We do this by comparing Gross-Pitaevskii
calculations with diffusion Monte Carlo calculations. We find very good
agreement between the results obtained by these two approaches once the dipole
dependence of the scattering length is taken into account. We also examine the
behavior of the condensate in non-isotropic traps.
