STABILITY OF 4-UNIT-CHARGE SYSTEMS - A QUANTUM MONTE-CARLO STUDY

The family of four-particle systems (M(+)m(+)M(-)m(-)) has been studie d by means of Monte Carlo techniques. Nonadiabatic explicitly correlat ed wave functions for different values of the mass ratio Mim have been obtained using a variational Monte Carlo optimization method. These w ave functions have been used in diffusion Monte Carlo simulations of ( M(+)m(+)M(-)m(-)) to compute exact ground-state energies. Our results enlarge the stability range of the mass ratio for these and for simila r less symmetric systems and address the problem of the stability of t he hydrogen-antihydrogen system. For the special case of the dipositro nium molecule (M=m) we report the ground-state energy, consistent with previous accurate calculations, and average values of various observa bles.