Charles W. Bauschlicher

The construction of modified virtual orbitals (MVO’s) which are suited for configuration interaction calculations

A simple method, requiring the work of a single SCF iteration, is presented for the construction of modified virtual orbitals (MVO’s). Test calculations on H2O, Ar, and two states of CH2 show that for the truncation of orbitals at the CI level, the MVO’s are far more efficient than canonical SCF virtual orbitals or such related SCF virtuals as improved virtual orbitals (IVO’s) and for some cases approach the efficiency of natural orbitals. MVO’s are shown to be suitable for configuration selection based on energy contributions. The CI wave function is observed to be more compact with MVO’s, allowing better interpretation of the results.

On the use of corresponding orbitals in the calculation of nonorthogonal transition moments

Full valence and first‐order CI wave functions are invariant with respect to unitary transformations among the valence orbitals. We exploit this degree of freedom and show that by transforming the valence orbitals into a corresponding orbital basis, nonorthogonal transition moment calculations become an easily managed task. Sample full valence calculations on several states of O+2 and OF are also presented.

Electronic structure of CaO. I

Electronic wavefunctions for 15 states of CaO arising (nominally) from six electron occupancies are calculated at the single configuration (sc) SCF level and analyzed qualitatively in terms of Mulliken populations and an approximate overlap criterion. The accuracy of the sc approximation is assessed and shown to be highly inadequate in several cases. Approximate Te’s are extracted from these results when warranted by the quality of the sc wavefunctions. An improved two configuration wavefunction for the lowest 1Σ+ state is also determined and discussed in detail.

The lower electronic states of ClOO: A computational investigation

Eight doublet and eight quartet states of ClOO were investigated by ab initio CI techniques. The potential energy surfaces of the four lowest energy doublet states of both A″ and A′ symmetry indicate that only the 1 2A″ state is bound. In contrast to the model provided by the HO2 radical, all of the excited doublet states investigated were repulsive with respect to dissociation to Cl+O2 and metastable or bound with respect to dissociation to ClO+O. The transitions to the excited states investigated span the visible and near UV spectral regions, but the transition moments indicate that they are very weak. Since the photolysis products are the same as those of the rapid thermal dissociation, photolysis is not expected to be an important atmospheric process. The soft bending potential for the 1 2A′ state and the shape of the 1 4A″ state in the entrance channel of the ClO+O → Cl+O2 reaction provide a qualitative explanation for the underprediction of the low temperature reaction rate by previous trajectory ca...

MCSCF wave functions for excited states of polar molecules: Application to BeO

A previously reported multiconfiguration self‐consistent field (MCSCF) algorithm based on the generalized Brillouin’s theorem is extended in order to treat excited states of polar molecules. In particular, the algorithm takes into account the proper treatment of nonorthogonality in the space of single excitations and invokes, when necessary, a constrained optimization procedure to prevent variational collapse of exited states. In addition, a configuration selection scheme (suitable for use in conjunction with extended configuration interaction methods) is proposed for the MCSCF procedure. The algorithm is used to study the low‐lying singlet states of BeO, a system which has not previously been studied using an MCSCF procedure. MCSCF wave functions are obtained for three 1Σ+ and two 1Π states. The 1Σ+ results are juxtaposed with comparable results for MgO in order to assess the generality of description presented here.

On the low‐lying states of MgO. II

Using a double zeta plus polarization basis set of Slater orbitals, full valence MCSCF (FVMCSCF) calculations were performed for the low‐lying states of MgO. For each state the FVMCSCF calculations were used to identify the important configurations which are then used in an MCSCF calculation and subsequently as references in a single and double excitation CI calculation. This approach is found to treat all states equivalently, with the maximum error in the computed Te’s and Re’s of 800 cm−1 and ∼0.03 , respectively. The b 3Σ+ state which has yet to be characterized experimentally is predicted to have a Te of ∼8300 cm−1 and a bond length of 1.79 A. A spectroscopic analysis of the potential curves indicates that their shapes are in quite reasonable agreement with the range of experimental results.

Core binding-energy shifts for free negative ions of oxygen: O0 to O2−

Abstract The free-ion 1 s binding-energy shifts for oxygen anions are investigated as a function of anionic charge. The ΔSCF method is used for calculation

CI superposition error caused by bond functions

Abstract The dissociation energy and the equilibrium bond length are calculated for CIO at the first order CI level for a variety of basis sets, consisting of both standard atomic centered basis sets and those including bond functions. The basis sets with bond function are found to have a CI superposition error many times that of the standard atomic centered basis sets.

Accurate ab initio calculations for the 1B1-1A1 separation in methylene

Accurate ab initio calculations have been performed on the 1B1 state of methylene. The basis set was of better than triple-zeta quality and included two sets of polarization functions. This work combined with previous work yields a 1A1-1B1 separation of 1.07 eV. This determination is compared to those using Franck-Condon factors.

On the electronic structure of the 2 1A1 state of methylene

The electronic structure of the 2 1A1 state of methylene is studied using multiconfiguration self-consistent-field and extended configuration interaction wavefunctions, as a prelude to a detailed investigation of the role of excited states in the chemistry of carbenes. Using selected one-electron properties as a guide, correlated wavefunctions obtained by different approaches are compared for the purpose of establishing qualitative differences between 1 1A1 and 2 1A1 states.