  In comparison with the accurate data on the on-top electron density n(0) in
the proton-embedded electron gas with the density parameter r_s in the range
1-12 obtained by diffusion Monte Carlo (DMC) simulations, we have successfully
constructed an alternative form of the exchange-correlation energy functional
in the density functional theory by imposing the constraint due to the cusp
theorem on the well-known Perdew-Burke-Ernzerhof (PBE) functional. Although PBE
does not, our functional, referred to as the cusp-corrected PBE (ccPBE),
reproduces the DMC data on n(0) in the entire range of r_s.
