Gas phase optical rotation calculated from coupled cluster theory with zero‐point vibrational corrections from density functional theory

Abstract

Molecular vibrations can have a significant influence on gas phase specific optical rotations. Mainly due to the large number of nuclear degrees of freedom in most chiral molecules, theoretical predictions of vibrational corrections quickly become prohibitively expensive. Here, we investigate an approach in which the purely electronic contribution is calculated at the coupled cluster singles and doubles level, while the zero-point vibrational correction is computed using the less demanding density functional theory (B3LYP functional). By comparing to experimental gas phase results for seven molecules and two wavelengths, we find that the mixed coupled cluster/B3LYP approach performs significantly better than pure B3LYP predictions. In fact, we find that it is more important to use high-level electron correlation for the electronic contribution than to include zero-point vibrational corrections.

Stereochemical analysis of (+)-limonene using theoretical and experimental NMR and chiroptical data

“…Using experimental and calculated chemical shifts for the populations, we have determined different populations. Interestingly, with incorporation of a solvent model, our populations based on enthalpies are very similar to the populations calculated by Partal Ureña et al [70] and Pedersen et al [45], both calculated in vacuo.…”

“…The conformers are the three equatorial conformers that we have found. The calculated ORD [45]. Likewise, the incorporation of vibrational averaging for six conformational rigid molecules did not improve the prediction of the optical rotation, maybe since the calculations were performed in vacuo and the experimental data were obtained in ethylcyclohexane [46].…”

“…Using our population mix based on experimental 13 C resonances, we can support this view: increasing the temperature increases the populations of conformer 2 and 3 which have calculated negative optical rotation values so that the decrease of the experimental values with increased temperature is explained. Pedersen et al [45] investigated the temperature effects on ORD values of limonene using coupled cluster calculations. They compared the results for three conformers with experimental gas phase data at 355 nm and 633 nm.…”

Time‐Dependent Density Functional Theory for Calculating Origin‐Independent Optical Rotation and Rotatory Strength Tensors

“…Another issue is the large magnitude of vibrational effects on optical rotations. [70][71][72] For a reliable comparison of computations with solution-phase data, it is most likely necessary to consider solvent and dynamic effects simultaneously. It has also been suggested to specifically improve upon calculated equilibrium values of optical rotation in conjunction with vibrational averaging by the use of correlated wavefunction-based calculations.…”

Cholesky Decomposition Techniques in Electronic Structure Theory

“…The decomposition was shown to give large savings for large basis sets with a variety of theoretical methods: Hartree-Fock (HF), density functional theory (DFT), second order Møller-Plesset perturbation theory (MP2), and the second-order approximate coupled cluster model (CC2) [34]. These implementations in the DALTON program has formed the basis for many computational developments and applications [35][36][37][38][39][40][41][42][43]. The CD strategy has subsequently been implemented in the MOLCAS program [44] for multiconfigurational methods (multiconfigurational self-consistent field (MCSCF) [45] and multiconfigurational second-order perturbation theory (CASPT2) [46]) as well as scaled opposite spin MP2 [47] and coupled cluster (CC) methods [44].…”