  We propose a variational wavefunction containing parameters to tune the
probabilities of all the possible onsite configurations for the periodic
Anderson model. We call it the full onsite-correlation wavefunction (FOWF).
This is a simple extension of the Gutzwiller wavefunction (GWF), in which one
parameter is included to tune the double occupancy of the f electrons at the
same site. We compare the energy of the GWF and the FOWF evaluated by the
variational Monte Carlo method and that obtained with the density-matrix
renormalization group method. We find that the energy is considerably improved
in the FOWF. On the other hand, the physical quantities do not change
significantly between these two wavefunctions as long as they describe the same
phase, such as the paramagnetic phase. From these results, we not only
demonstrate the improvement by the FOWF, but we also gain insights on the
applicability and limitation of the GWF to the periodic Anderson model.
