Configuration-interaction studies of Bose-Einstein condensates

A direct configuration-interaction (CI) approach for studies of Bose-Einstein condensates has been developed and implemented. The reference state is obtained by solving the Hartree-Fock equation in a nonorthogonal Gaussian basis. The CI problem is solved by diagonalizing the Hamiltonian constructed in a many-body basis generated using the orthogonal canonical orbital basis obtained in a Hartree-Fock calculation. For Hamiltonian matrices, which are too large for full diagonalization, a direct iterative diagonalization scheme is employed for obtaining the lowest-lying eigenstates. The computational methods were tested by applications to Bose-Einstein condensates using various isotropic and anisotropic trap geometries.