Rolf Seeger

Self‐consistent molecular orbital methods. XX. A basis set for correlated wave functions

A contracted Gaussian basis set (6‐311G**) is developed by optimizing exponents and coefficients at the Mo/ller–Plesset (MP) second‐order level for the ground states of first‐row atoms. This has a triple split in the valence s and p shells together with a single set of uncontracted polarization functions on each atom. The basis is tested by computing structures and energies for some simple molecules at various levels of MP theory and comparing with experiment.

Self‐consistent molecular orbital methods. XVIII. Constraints and stability in Hartree–Fock theory

Constraints that may be applied to the spin orbitals used in Hartree–Fock theory are classified and discussed. Once a constrained stationary wavefunction has been obtained by a self‐consistent procedure, it may be tested for stability both internally (with constraints remaining) and externally (with some constraints removed). Methods for carrying out these tests are presented. In addition, a general technique is described for further energy minimization following detection of an instability.

Isomeric structures of protonated carbon dioxide

Equilibrium structures of protonated carbon dioxide are explored by ab initio molecular orbital theory. The hydroxycarbonyl cation (I) is found to be most stable; the associated proton affinity is calculated to be 130 kcal/mol, in reasonable agreement with experimental data. The dioxiryl cation (IV), about 90 kcal/mol less stable than I, is found to be a second minimum on the potential energy surface. The reaction path connecting isomers I and IV appears to involve barriers of significant magnitude; consequently, it is possible that both HCO+2 and CO2H+ may be detectible experimentally or serve as reaction intermediates.

Experimental Versus Theoretical Electron Densities. Small Molecules, Large Molecules, and Salts

Abstract High quality ab initio calculations of electron deformation densities and comparisons with available experimental results are presented for small molecules. AHF (approximate Hartree-Fock) basis set and electron correlation effects are assessed. The high quality of the 4-31G + BF (bond functions) basis set for the computation of deformation densities is established for small molecules. Comparison of 4-31G + BF electron densities with all available experimental data is made for some selected large organic molecules. Errors and problems in the experimental and theoretical methods are discussed. Crystal effects such as hydrogen bonding and ion effects in salts are estimated. It is shown that all the effects considered (i.e., near HF basis set, correlation, hydrogen bonding and ion effects) are small compared to possible experimental uncertainties. Thus, at present, economical 4-31G + BF calculations of isolated molecules are sufficiently accurate for comparisons with any type of experimental determin...

Electron density in Mo/ller–Plesset theory

The Mo/ller–Plesset theorem states that for the electronic Hamiltonian in the form H = JpFp+V, where the eigenfunctions of Fp are the Hartree–Fock molecular spin orbitals and the eigenvalues are the one‐electron energies, by treating V as a perturbation the first order term in the expansion of the electron density vanishes. In spite of this, some one‐electron properties are not given at the H–F level. This Note presents the expression for the second order correction to the electron density.

Carbon-beryllium binding in CH2Be

Ab initio molecular orbital theory is used to study carbon-beryllium binding in the lowest singlet and triplet states of CH2Be. When electron correlation is included, both singlet and triplet states are significantly bound relative to the ground states of CH2 and Be fragments.

Integrals of gaussian and continuum functions for polyatomic molecules. An addition theorem for solid harmonic gaussians

Abstract An addition theorem for solid harmonic gaussian functions in terms of surface spherical harmonics is derived and presented in a form particularly useful for evaluating molecular integrals involving gaussian and continuum functions on array processors.