Self-consistent Field Configuration Interaction Calculations Research Articles

Adiabatic versus diabatic descriptions of the lowest Rydberg and valence $1^\Sigma ^{+}$Σ+1 states of HCl

In this contribution we first report new ab initio self-consistent field configuration interaction calculations of the first excited adiabatic potential of (1)Σ(+) symmetry, the 2(1)Σ(+) or B(1)Σ(+) state, which presents two minima and can thus be seen as made up of the Rydberg E(1)Σ(+) and the valence V(1)Σ(+) states. Based on the computed 2(1)Σ(+) potential, we devised a theoretical procedure to compute the vibronic structure in order to try to explain the energy levels observed in the region above 76 254.4 cm(-1) which display an irregular vibrational structure, indicative of spectral perturbations. We try to find out which representation of the electronic states, the diabatic or the adiabatic one, is best suited to replicate the lowest observed vibronic levels of the E and V states. To this end, we deduce, from the 2(1)Σ(+) potential and its complementary adiabatic potential, two diabatic potentials. We then carry out a coupled equation treatment based on these diabatic potentials. The results of this treatment indicate that, in the present case, the adiabatic representation is better than the diabatic one to describe the observed vibronic levels. This is due, as expected, to the existence of a strong electrostatic interaction between the two diabatic potentials.

Crystal field and molecular orbital calculation of the optical transitions in Ce doped alkaline earth sulfide (MgS, CaS, SrS, and BaS) phosphors

The effect that different alkaline earth sulfide host materials have on the Ce +3 5d→4f optical transitions is investigated using self-consistent field-configuration interaction calculations. The results are in excellent agreement with the experimentally determined transition energies for MgS : Ce, CaS : Ce, SrS : Ce, and BaS : Ce. The red shift of the spectroscopy of BaS : Ce relative to that of SrS : Ce was correctly predicted. In addition, calculated oscillator strengths of the electronic transitions in SrS : Ce and BaS : Ce were fit with Gaussian shapes to model the vibronic structure. Both absorption and emission spectra were generated, and were found to have good agreement with experimental spectra. Point charge-crystal-field calculations were employed in an attempt to account for the experimentally observed trend, but failed to do so. A population analysis of the configuration interaction states indicates that the trend in emission energies is caused by differing extents of covalency experienced by the Ce 5d orbitals in the various host materials.