Natural orbital expansions of highly accurate three-body wavefunctions

Natural orbital expansions are considered for highly accurate three-body wavefunctions written in the relative coordinates r(32), r(31) and r(21). Our present method is applied to the ground S (L = 0)-state wavefunctions of the Ps-and H-infinity(-) ions. Our best variational energies computed herein for these systems are E (Ps(-)) = -0.262 005 070 232 980 107 7666 au and E (H-infinity(-)) = -0.527 751016 544 377 196 5865 au, respectively. The variational wavefunctions determined for these systems contain between 2000 and 4200 exponential basis functions. In general, the natural orbital expansions of these functions are compact and rapidly convergent functions, which are represented as linear combinations of some relatively simple functions. The natural orbitals can be very useful in various applications, including photodetachment and scattering problems.