Off-Diagonal Long-Range Order (odlro) and Ground State Properties of Liquid Helium.

An independent calculation of the condensate fraction and the ground state energy of liquid helium is given. We use the Frohlich ansatz for the second reduced density matrix in conjunction with the ODLRO hypothesis for liquid helium below the critical temperature. Frohlich's ansatz is shown to be consistent with numerical calculations of the ground state properties of liquid helium. The ground state energy was -5.10(DEGREES)K, close to the experimental value. The condensate fraction turned out to be about 10% which is within the margin of error of recent neutron scattering experiments and agrees with other theoretical calculations.