High precision variational calculations for H2+

A double basis set in Hylleraas coordinates is used to obtain improved variational upper bounds for the nonrelativistic energy of the 1 S-1 (upsilon = 0, R = 0),2 S-1 (upsilon = 1,R = 0) and 2 (3)p(upsilon =0, R = 1) states of H-2(+). This method shows a remarkable convergence rate for relatively compact basis set expansions. A comparison with the most recent work is made. The accuracy of the wavefunctions is tested using the electron-proton Kato cusp condition.