Comment on "Universally Diverging Gruneisen Parameter and the Magnetocaloric Effect Close to a Quantum Critical Point"

In a recent Letter, Zhu et al. [L. Zhu et al., Phys. Rev. Lett. 91, 066404 (2003)], obtained the divergence of the Gruneisen ratio close to a quantum critical point (QCP). We show that, in the case the effective dimension associated with the QCP is larger that the upper critical dimension (d+z >4), their result is inconsistent with the thermodynamic Ehrenfest equation. We discuss the reasons for this inconsistency.