The ground-state energies of interacting bosons are computed beyond the mean-field approximation by a new method which we call reduced Hamiltonian interpolation (RHI). In this interpolation the $N$-particle Hamiltonian is represented through a sequence of $p$-particle expanded and reduced Hamiltonians that give upper and lower bounds on the true energy. A synthesis of ideas from $N$-representability and dimensional interpolation, the RHI interpolates over the number $p$ of quasiparticles (equivalent to spatial dimension) to calculate the $N$-particle energy as the mean of close upper and lower bounds. Application to bosons with harmonic interactions yields more than $99\%$ of the correlation energy.

• Received 12 August 1999

DOI:https://doi.org/10.1103/PhysRevLett.83.5185