  A dilute Bose gas system is studied using the functional Schr\"{o}dinger
picture theory. The ground state properties are obtained by solving the
infinite dimensional Schr\"{o}dinger equation variationally. It is shown that a
shifted Gaussian trial wavefunctional enables us to calculate a higher order
correction, which corresponds to the fluctuation contribution from the
condensate. The obtained term is compared with the quantum correction arising
from the low energy $3 \to 3$ scattering.

Statistical Mechanics