Correlated Configuration Interaction Wave Functions Research Articles

Self-consistent embedding theory for locally correlated configuration interaction wave functions in condensed matter

We present new developments on a density-based embedding strategy for the electronic structure of localized feature in periodic, metallic systems [see T. Kluner et al., J. Chem. Phys. 116, 42 (2002), and references therein]. The total system is decomposed into an embedded cluster and a background, where the background density is regarded as fixed. Its effect on the embedded cluster is modeled as a one-electron potential derived from density functional theory. We first discuss details on the evaluation of the various contributions to the embedding potential and provide a strategy to incorporate the use of ultrasoft pseudopotentials in a consistent fashion. The embedding potential is obtained self-consistently with respect to both the total and embedded cluster densities in the embedding region, within the framework of a frozen background density. A strategy for accomplishing this self-consistency in a numerically stable manner is presented. Finally, we demonstrate how dynamical correlation effects can be treated within this embedding framework via the multireference singles and doubles configuration interaction method. Two applications of the embedding theory are presented. The first example considers a Cu dimer embedded in the (111) surface of Cu, where we explore the effects of different models for the kinetic energy potential. We find that the embedded Cu density is reasonably well-described using simple models for the kinetic energy. The second, more challenging example involves the adsorption of Co on the (111) surface of Cu, which has been probed experimentally with scanning tunneling microscopy [H. C. Manoharan et al., Nature (London) 403, 512 (2000)]. In contrast to Kohn-Sham density functional theory, our embedding approach predicts the correct spin-compensated ground state.

Theoretical spectroscopy of the NO radical. III. Λ doubling and predissociation in the C 2Π state

The Λ doubling of the C 2Π state of NO is calculated by considering the heterogeneous couplings (spin–orbit and rotational angular momentum) between the C 2Π and the first three 2Σ+ states plus the homogeneous interaction of the C 2Π with the B 2Π state. All wave functions and energies result from highly correlated configuration interaction wave functions. A transformation from the adiabatic to the diabatic basis is performed by employing the radial coupling between the two 2Π states. The perturbation matrix is solved in the diabatic basis and leads directly to the eigenvectors and eigenvalues of the Λ components. It is found that for J≥3/2 the Λ components are completely mixed and can therefore not be labeled according to their Ω values any more. Vibrational averaging leads to a calculated value of 0.019 cm−1 (J=0.5, v=0) compared to the measured value of 0.016 cm−1 for the Λ doubling. The predissociation process of the C 2Π state is calculated in the adiabatic basis; the mechanism is found to be caused solely by the spin–orbit interaction with the a 4Π state.

Explicitly correlated configuration interaction wave functions for the He atom using correlated Gaussians

Explicitly correlated configuration interaction wave functions for the He atom using correlated Gaussians

Elastic and Inelastic Electron Scattering by He and Ne Atoms in Their Ground States

A study of elastic and inelastic scattering of electrons by He and Ne atoms in their ground states is made within the framework of the first Born approximation. For the elastic case a partial-wave analysis is also carried out. Properly correlated configuration interaction wave functions, and also Hartree-Fock wave functions, are used throughout. It is shown that for an accurate description of both elastic and inelastic scattering, a correlated wave function is essential. A table of elastic and inelastic electron scattering factors for the elements studied is given.