  Density functional theory (DFT) has been used to estimate vacancy formation
enthalpy (H_fv) for a few transition metals like nickel (Ni) and copper (Cu).
It is shown that, for these metals, H_fv is underestimated considerably by DFT.
The aim of the present work is to bridge the gap between the estimates made by
DFT calculations and experiments. The sources of this discrepancy are
identified as to be related to the opening up of the surface like region
surrounding the vacancy, and the temperature induced anharmonic contribution.
The surface related correction to H_fv has been estimated by a jellium based
model originally proposed by Mattsson et al. [Phys. Rev. B 73 (2006) 195123]
and subsequently modified by Nandi et al. [J. Phys.:Cond. Matt. 22 (2010)
345501]. In this paper, we have estimated the temperature induced anharmonic
contribution to H_fv using density functional perturbation theory. Finally, it
is shown that incorporation of both the surface correction and anharmonic
correction to H_fv, results in a better agreement with the experimental data.
