Single-Center Configuration-Interaction Calculations on the Ground State of H3+

Abstract

Results of several single-center expansion configuration-interaction calculations are reported for the ground state of the H3+ molecule. A basis set of D3h symmetry-adapted Slater-type orbitals is located at the center of the molecule, which forms an equilateral triangle, and the nonlinear parameters are extensively optimized. Using an 85-configuration wavefunction we obtain an energy of − 1.3392 hartree, vibration frequencies of ν1 = 3450 cm−1, ν2 = 2850 cm−1, and a bond length of Re = 1.64 bohr. The calculated energy is in error by about 4 kcal/mole compared to the estimated exact energy. The computed geometry and vibration frequencies agree to within a few percent with values reported in the literature. An analysis of the convergence of our single-center wavefunction is given. The Joy-Handler l−4 rule appears to be approximately obeyed, and our results indicate that convergence is at least as rapid for triangular H3+ as for linear H3+. The energy associated with the Hartree–Fock part of our wavefunction is estimated to be − 1.298 hartree (99.8% of exact). This, together with a correlation energy of about 0.041 hartree (91% of exact), gives our best total energy of − 1.339 hartree.