Scaled AMO calculations on the hydrogen molecule. III. The 1s2s 3∑ state

The potential energy curve for the 1s2s ³∑ state of the hydrogen molecule is calculated in a scaled version of the AMO approximation. Deviations from a simple potential curve occur. The agreement with experimental data is found to be better for the present state than for the 1sσ2pσ ¹∑ state studied in a previous paper.     

Scaled AMO calculations on the hydrogen molecule IV. General remarks

The scaled version of the AMO method as applied to the hydrogen molecule is discussed. Additional information about previous calculations on H₂ with similar approximations together with computations on excited states (states corresponding to the next lowest root of the secular equation) are reported. The asymptotic behaviour is particularly investigated.     

Hybrid Slater–Gaussian-type 1s orbitals for the 1∑ ground state of H2 and He

Introduction of noninteger powers of r (or the elliptical coordinate ξ) in the definition of the 1s AO is shown to give better approximate wave-functions for the ground states of H₂ and He than other functions of comparable complexity. This trend is examined for various definitions of hybrid Slater–Gaussian orbitals using a limited CI . The best optimized single-term expansion energy is only 0.000160 a.u. above the “SCF limit” for H₂ at R = 1.4 a.u. and 0.000382 a.u. for He at R = 1.3 a.u.     

Ab initio Hartree-Fock calculations of electronic wave functions for the c 3πu state of H2

Theoretical electronic wave functions, potential curves, and expectation values of some one-electron properties are given for the c³II_u state of the hydrogen molecule. The calculations are carried out by the matrix Hartree-Fock method and use a 2-center basis of Slater-type orbitals. A total energy of ?0.7292 a.u. is obtained in the best calculation. Our potential curve is reasonably consistent with that calculated by Browne, but we have examined the region of small internuclear distances (those at and below R_e for the ground state) more extensively than any previous calculation. At R ≦ 1.6 a.u. our calculated potential curve is in excellent agreement with experiment.     

Multi‐channel coupling effects for electronic excitations leading to the b3∑, a3∑, and c3∏u states of H2

In this work we use the unitarized distorted wave method to study the effect of multi‐channel coupling on the calculated electronic excitation cross sections in H₂. Specifically, such an effect for electronic excitations leading to the excited states b³∑, a³∑, and c³∏_u for incident energies varying from 15 to 60 eV is studied. Our results have shown that converged cross sections can be obtained with the inclusion of only triplet intermediate states, except for energies near the excitation thresholds, where the inclusion of singlet intermediate states is important. Also, convergence improves with increasing energies for all excitations considered. Comparison of our calculated cross sections with available experimental and other theoretical results is encouraging. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Pairwise correlated generalized valence bond model of electronic structure. VII. The b 3∑ state of H2

A modification of the overlap approximation for triplet pair correlation energies is presented. The modification allows the use of either the canonical absolute overlap or the minimum absolute overlap. When applied to the b ³∑ state of H₂, this approximation reproduces the observed correlation energy to within 0.0002 hartree (or ±3%) for all internuclear distances from 1.3 bohr to infinity.     

Theoretical calculations on σ-systems. III. Alkyl halides and alkanes

Various aspects of Del Re's method, its extension and correlation with important properties such as nuclear quadrupole coupling constants and spin-spin coupling constants are discussed. The Del Re parameters for the C–I bond have been evaluated and those for the C–F bond modified. The bond energies and the heats of formation for several σ-systems have been calculated; the energies of a “bond-orbital” for several alkanes have been found to be related with their ionization potentials.     

A configuration interaction study of the four lowest 1∑+ states of the LiH molecule

A configuration interaction study was completed on the ¹∑⁺ states of the LiH molecule using a nonorthogonal one-electron basis in elliptical coordinates. A few wave functions with highly optimized parameters were obtained for the X¹∑⁺ and A¹∑⁺ states and combined to construct a larger wave function which gave improved results for both states over a wide range of R values. The third and fourth roots are also reported since the wave function is extensive enough to give good upper bounds for the two states. Calculations were completed for 34 values R in the range 1 ≤ R ≤ 10 bohr (b). The calculated X¹∑⁺ curve has a minimum at Re = 3.060b (3.015b), with E(Re) = ?8.0556 Hartree (H) (?8.0704), μ(Re) = ?5.89 debye (d) (?5.88d) and μ/(R dμ/dR)|_Re = 1.75 (1.80 ± 0.3). For the A¹∑⁺ state, Re = 4.928b (4.906b), E(Re) = ?7.9372H(?7.9496H), μ(Re) = +3.96d and μ/(R dμ/dR)|_Re = ?-0.471. The values in parentheses are experimental results for comparison. The numerical vibrational and rotational analysis agreed well with experiment for both states. The A¹∑⁺ state exhibited a pronounced negative anharmonicity. Both states show strong interaction of three zeroth-order configurations, the nature of which changes considerably with R. The thus far unobserved second excited state has two minima, a metastable one at R = 3.70b and another at R ≈ 10.00b. The third excited state also appears to have a minimum at R ≈ 7.00b.     

Theoretical calculations on σ-systems,part 1: Ethers and chloro-substituted ethers

The charge on each atom of some ethers and chloro-substituted ethers, their dipole moments and the quadrupole coupling constants of the chloroethers have been calculated with the method suggested by Del Re. There appears to be an intimate connection between the charge density on the oxygen atoms and the capacity of forming hydrogen bond.