The Hylleraas-configuration-interaction (H-CI) method has been applied to the first 3Σ+u excited state of the H+3 molecular ion. Besides the ground state, this is the only known bound state of H+3, albeit with a very weak minimum of 8.428 kcal/mol. The equilibrium geometry and the minimum energy have been determined. The Hylleraas-CI energy of −1.116 102 7 a.u. at an equidistant nuclear separation of 2.454 bohr is the lowest reported so far. The vibrational force constants and vibrational frequencies also have been computed.
Accurate a b i n i t i o potential energy computations for the H4 system: Tests of some analytic potential energy surfaces J. Chem. Phys. 95, 4331 (1991); 10.1063/1.461757 Gaussian functions in Hylleraasconfiguration interaction calculations: Potential curves for the e 3∑+ u and the f 3∑+ u states of hydrogen J. Chem. Phys. 92, 4941 (1990); 10.1063/1.457711 Potentialenergy surfaces for Pt2+H and Pt+H interactions J. Chem. Phys. 92, 541 (1990); 10.1063/1.458457 Gaussian functions in Hylleraasconfiguration interaction calculations. II. Potential curves for the b 3Σ+ u and the e 3Σ+ u states of hydrogenThe near-equilibrium potential-energy surface of the 'A ; ground state ofH3+ has been calculated at 69 different points with the Hylleraas-configuration interaction method using 13s3pld 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 H3+ 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 -I) 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.
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