Abstract
The binding energy of positronium molecules is calculated variationally by using extensive Hylleraas-type wave functions in which all six interparticle coordinates are used. The binding energy against dissociation into two positronium atoms is determined as 0.0302 Ry. The present result is consistent with the value of 0.0303±0.0005 Ry, obtained by Lee using the Green’s-function Monte Carlo method.