Gaussian functions in Hylleraas-configuration interaction calculations. V. An accurate ab initio H+3 potential-energy surface

The near-equilibrium potential-energy surface of the 1A'1 ground state of H+3 has been calculated at 69 different points with the Hylleraas-configuration interaction method using 13s3p1d Cartesian Gaussian basis functions. This new surface is found to be substantially lower in absolute energy than all previous surface calculations. The equilibrium energy of the H+3 molecule has also been calculated with a larger 13s5p3d basis set. The minimum energy was found to be E=-1.343 827 9 hartrees at an internuclear distance of R=1.6500 bohrs in the equilateral triangle configuration. This energy is significantly (>70 cm-1) lower than the previous best published variational calculation and is outside and below the error bars of the latest quantum Monte Carlo calculation. In addition, a medium-sized basis set of 13s4p2d orbitals was used to predict that the equilibrium separation is R=1.6499 bohrs