Rick A. Kendall

Benchmark calculations with correlated molecular wave functions. II. Configuration interaction calculations on first row diatomic hydrides

Potential energy functions have been calculated for the electronic ground states of the first row diatomic hydrides BH, CH, NH, OH, and HF using single‐ (HF+1+2) and multi‐ (GVB+1+2 and CAS+1+2) reference internally contracted single and double excitation configuration interaction (CI) wave functions. The convergence of the derived spectroscopic constants and dissociation energies with respect to systematic increases in the size of the one‐particle basis set has been investigated for each method using the correlation consistent basis sets of Dunning and co‐workers. The effect of augmenting the basis sets with extra diffuse functions has also been addressed. Using sets of double (cc‐pVDZ) through quintuple (cc‐pV5Z) zeta quality, the complete basis set (CBS) limits for Ee, De, re, and ωe have been estimated for each theoretical method by taking advantage of the regular convergence behavior. The estimated CBS limits are compared to the available experimental results, and the intrinsic errors associated with...

BENCHMARK CALCULATIONS WITH CORRELATED MOLECULAR WAVE FUNCTIONS. III: CONFIGURATION INTERACTION CALCULATIONS ON FIRST ROW HOMONUCLEAR DIATOMICS

Using correlation consistent basis sets from double through quintuple zeta quality, potential energy functions have been calculated for the electronic ground states of the first row homonuclear diatomic molecules B2, C2, N2, O2, and F2 using single and double excitation configuration interaction (HF+1+2, GVB+1+2, and CAS+1+2) wave functions. Spectroscopic constants have been calculated for each species and compared to experiment. The dependence of the calculated spectroscopic constants on systematic extensions of the one‐particle basis set are, in general, found to be very regular. By fitting the directly calculated values with a simple exponential function, accurate estimates of the complete basis set (CBS) limit for Ee, De, and re have been obtained for each level of theory. The estimated CBS limits are compared to the available experimental results, and the intrinsic errors associated with each theoretical method are discussed. In addition, the accuracy of the internally contracted CAS+1+2 method is co...

Ab initio studies of the structures and energies of the H−(H2O) and H−(H2O)2 complexes

Accurate calculations for the H−(H2O) complex with extended basis sets are reported at the restricted Hartree–Fock (RHF) through the fourth‐order Mo/ller–Plesset (MP) perturbation levels of theory. In the equilibrium geometry of the H−(H2O) complex the H− anion is found to lie almost along one of the H–O bond directions. The H–H− distance proved to be very sensitive to electron correlation effects: it is 1.8 and 1.4 A at the RHF and MP2 levels, respectively. The interaction energy between H− and H2O at the MP4 level including conterpoise corrections for basis set superposition error, depending upon the basis set used, is found to range from 16.2 to 16.9 kcal/mol, and the electron correlation is responsible for one‐third of this value. The enthalpy of formation of H−(H2O) is estimated to be from −15.2 to −16.0 kcal/mol compared with the experimental value of −17.3±1.2 kcal/mol. The vibrational frequencies of H−(H2O) are also reported. The H−(H2O)2 complex is also studied by using a polarized double zeta ba...

Associative electron detachment: O−+H→OH+e−

Associative Electron Detachment processes are important experimental events that can readily be modeled using modern theoretical methods. Experimental methods to date have only allowed one to obtained the relative vibrational distribution of the neutral product molecules. Using a non‐Born‐Oppenheimer, nonadiabatic, viewpoint that utilizes a fully ab initio approach, we are able to obtain absolute rates (∼104 s for the O−+H system) for transitions from an initial state specified by collision energy and impact parameter, to specific vibrational and rotational states of the neutral OH and a detached electron. The fact that these rates are slow for the O−+H system is due to the large electron affinity of OH (1.8 eV). These rates have an obtuse propensity favoring vibrationally and rotationally hot products. This propensity arises from contributions that are independent and dependent of the angular momentum of the system, an aspect that is of substantial experimental interest. A detailed study of O−+H→OH(V’,J’...