Yuh-Kang Pan

An accurate ab initio calculation of the Ne2 potential

Abstract The Moller—Plesset perturbation calculations are carried out for the neon-dimer interaction potential, using an extended basis set augmented by the mid-bond basis functions. Theoretical analysis is given to justify the need and the proper use of bond functions. The calculated potential minimum, 3.12 A, and the energy, − 130.07 μhartree, are in close agreement with the results of several empirical potentials.

An accurate ab initio potential energy surface of HeH2O

Abstract We present an accurate calculation of the intermolecular potential surface for the van der Waals complex HeH2O using complete fourth-order Moller-Plesset perturbation theory (MP4) with an efficient basis set containing bond functions. The calculation gives a global minimum at R=3.15 A , θ=105°, φ=0° (in a Jacobi coordinate system) with a minimum energy De=31.8 cm−1, along with barriers of 13.4 and 12.6 cm−1 for in-plane rotation at θ=0° and 180°, respectively, and a barrier of 20.0 cm−1 for out-of-plane rotation at θ=105°, φ=90°. The potential energy surface is compared with previously published surfaces for HeH2O, and with the potential energy surface for ArH2O.

Calculation of photoelectron spectra of chloromethanes

Abstract Photoelectron spectra of chloromethanes have been calculated by the SCF Xα SW method. Results of the present work are in significantly better quantitative agreement with experiment data than are the results of other theoretical methods.

An ab initio study of the intermolecular potential surfaces of HeCH4 and NeCH4

Abstract The intermolecular potential surfaces for the Van der Waals complexes HeCH 4 and NeCH 4 are studied by ab initio theory using complete fourth-order Moller-Plesset perturbation theory (MP4) with an efficient basis set containing bond functions. For HeCH 4 , the global minimum occurs at R = 3.4 A , θ = 180°, φ = 0° (in a Jacobi coordinate system) with a minimum energy D e = −26.2 cm −1 . For NeCH 4 , the global minimum occurs at R = 3.5 A , θ = 180°, φ = 0° with a minimum energy D e = −59.0 cm −1 . Two saddle points were found for each of the systems. The potential energy surfaces are compared with the semiempirical surfaces and recent ab initio results on the same systems.

H2S·HOH or H2O·HSH, which is more stable in the water-hydrogen sulfide complex?

High-level ab initio calculations are carried out to study the relative stability of the two hydrogen bonded structures of water-hydrogen sulfide complex, one with water as the proton donor (A) and the other with hydrogen sulfide as the proton donor (B). The results show that structure A is considerably more stable than B at the correlated level, which is in contrast with previous results obtained from Hartree-Fock calculations.

Calculation of bond dissociation energies of diatomic molecules using bond function basis sets with counterpoise corrections

Bond function basis sets combined with the counterpoise procedure are used to calculate the molecular dissociation energies D{sub e} of 24 diatomic molecules and ions. The calculated values of D{sub e} are compared to those without bond functions and/or counterpoise corrections. The equilibrium bond lengths r{sub e}, and harmonic frequencies w{sub e} are also calculated for a few selected molecules. The calculations at the fourth-order-Moller-Plesset approximation (MP4) have consistently recovered about 95-99% of the experimental values for D{sub e}, compared to as low as 75% without use of bond functions. The calculated values of r{sub 3} are typically 0.01 {Angstrom} larger than the experimental values, and the calculated values of w{sub e} are over 95% of the experimental values. 37 refs., 2 tabs.

Calculation of photoelectron spectra of group IV tetrachlorides and carbon tetrahalides by SCF-Xα-SW method

Photoelectron spectra and one-electron eigenfunctions of group IV tetrachlorides, ACl4, where A = C, Si, Ge, Sn and carbon tetrahalides, CB4, where B = F, Cl, Br, I, have been calculated by SCF-Xα-SW method. Excellent agreement is obtained with the observed photoelectron spectra. The radius reduction factors of atomic sphereFrwere adjusted instead of changing individual atomic radii. The comparison of photoelectron spectra and one-electron eigenfunctions for molecules ACl4 for different central atoms A and halogen atoms B is discussed.

A new approach to theab initio energy of the homodesmic reaction for the resonance energy of benzene

SummaryA scheme of the basis set superposition error (BSSE) correction is first proposed and introduced to determine theab initio energy of the homodesmic reaction for the resonance energy of benzene. Calculations with 6-31G*(5D) and 6-31G*(6D) basis sets at the complete fourth-order Møller-Plesset perturbation level furnish the energy value of 21.35 kcal/mol after the correction, which is in complete agreement with the experimental value of 21.3±0.2 kcal/mol. The energy values at the lower theoretical levels are generally underestimated but they are superior to the uncorrected values. The inclusion of triple excitations displays the dominant contribution of the correlation energy. Detailed analysis of the results reveals some of the similarities between the homodesmic reaction of benzene and the interaction of van der Waals molecule, which provides further justification of the BSSE correction scheme presented in this study.

An SCF-Xα-MS study of the photoelectron spectra and electronic structures of methylene dihalides

Abstract The photoelectron spectra and electronic structures of the methylene dihalides, CH 2 X 2 (X = F, Cl, Br and I), have been calculated by the overtapping-spheres SCF- X α-MS method. The results are in good agreement with experimental data. Calculated assignments of the spectra are also presented and interpreted by assuming interaction between lone-pair and bonding orbitals.

Radiative lifetimes of the singlet oxygen molecule

Abstract Radiative lifetimes of the a I Δ g and b 1 Σ + g states of the oxygen molecule have been calculated by improving the approximations used by Carr et al. The present calculation gives the correct order of magnitude for the radiative lifetime of both states.