Theoretical and Experimental Spectroscopy of the S₂ State of CHF and CDF: Dynamically Weighted Multireference Configuration Interaction Calculations for High-Lying Electronic States

Abstract

Dynamically adjusting the weights in state-averaged multiconfigurational self-consistent field (SA-MCSCF) calculations using an energy-dependent functional allows the electronic wave function to smoothly evolve across the potential energy surface (PES) and correctly preserves differing asymptotic electronic-state degeneracy patterns. We have developed a generalized dynamic weighting (GDW) method to treat high-lying electronic states. To test the method, a global PES was constructed for the S 2 ( B) state of CHF (CDF), which lies nearly 31000 cm -1 above the minimum of the ground state. The GDW method was used to produce SA-MCSCF reference states for subsequent multireference configuration interaction (MRCI) calculations, whose Davidson-corrected energies were extrapolated to the complete basis set limit. Quantum mechanical vibrational energy calculations for CDF were performed using the fitted PES, and the predicted energy levels are in excellent agreement with an extensive set of experimentally determined (optical-optical double resonance) levels, with a mean unsigned error of only 12 cm -1 .

Communication: Rigorous quantum dynamics of O + O2 exchange reactions on an ab initio potential energy surface substantiate the negative temperature dependence of rate coefficients

“…It has recently been shown by Dawes et al 21,22 that the "reef"-like saddle point present in many previous ozone PESs is an artifact of the electronic structure model used to generate the PESs. The new Dawes-LolurLi-Jiang-Guo (DLLJG) PES, obtained with a dynamically weighted 23,24 explicitly-correlated multi-reference configuration interaction [25][26][27] approach with the Davidson correction 28 and spin-orbit correction (DW-MRCI-F12+Q), is "reef"-free, thus qualitatively different from all previous ozone PESs. 16,20,29 The disappearance of the "reef" structure essentially results from the employment of a large basis set, larger active configuration spaces, and dynamical weighting of excited states.…”

Spectroscopy and dynamics of the predissociated, quasi-linear S2 state of chlorocarbene

“…Calculations relating to any particular molecular state of interest were performed using a dynamically weighted full-valence CASSCF procedure, focusing maximum weight on the state of interest (the singlet and triplet states were computed separately). 23 This was used as the reference for subsequent Davidson-corrected MRCI(+Q) calculations. The MOLPRO code was used to perform all of the electronic structure calculations reported here.…”

Communication: An accurate global potential energy surface for the ground electronic state of ozone

“…15 To briefly summarize, we found that the height of the submerged reef and depth of the vdW well are substantially reduced by both basis set and active space completeness. We followed the switch in character between the ground state and an excited state correlated with O 2 ( 1 g ) + O( 1 D g ) products and noted that if all 13 singlet states were included using a dynamically weighted state-averaged method 25,26 (DW-SA-CASSCF), then the transition was better behaved and the reef all but disappeared. Finally, by including more than one reference state in the internally contracted icMRCI (thus increasing the number of contracted configurations and reducing the effect of internal contraction), we obtained a MEP that is a monotonic function of the distance to the dissociating O-atom (no reef feature).…”