The stability and structure of Li+Ps2 and Na+Ps2

The fixed-core stochastic variational method has been used to demonstrate the existence of an electronically stable ground state for the Li(+)Ps(2) and Na(+)Ps(2) systems. The stability of Li(+)Ps(2) has been indicated previously in an ab initio calculation by Varga, but the present estimate of the binding energy is much closer to convergence. The Li(+)Ps(2) system has a binding energy of 0.013 149 Hartree and a 2 gamma annihilation rate of 3.86 x 10(9) s(-1). The Na(+)Ps(2) system has a binding energy of 0.005736 Hartree and an annihilation rate of 4.02 x 10(9) s(-1). Examination of the interparticle expectation values, correlation functions and the annihilation rates suggests that both of these systems can be best described as a Ps(2) molecule weakly bound to an alkali atom cation.