Correlated Wavefunction for the Li Atom*

Accurate wavefunctions are extremely valuable as tools for gaining understanding of quantum systems. Here we use a wavefunction explicitly containing all the interparticle distances to obtain a highly precise description of the ground state of the Li atom. In contrast to the widely used Hylleraas approach (in which the interelectron distances enter the wavefunction only as integer powers), our wavefunction exhibits an exponential dependence on all the interparticle distances, with a spatial dependence (before imposing spin and symmetry restrictions) of the form $\sum_{n=1}^N c_n \exp(-w_1r_1-w_2r_2-w_3r_3-u_1r_{23} -u_2r_{13}-u_3r_{12})$, where $r_i$ are electron-nuclear distances, $r_{ij}$ are electron-electron distances, and $w_i$ and $u_i$ are parameters. When the nonlinear parameters are carefully optimized (a nontrivial task), this type of basis causes a far more rapid convergence (with $N$) than the Hylleraas basis. We will survey the results we have obtained and compare with other studies of the Li atom.