Accurate calculation of the intensity dependence of the refractive index using polarized basis sets

Accurate calculation of optically induced birefringences in chiral systems using efficient polarized basis sets

Using state-of-the-art ab initio methodology, we evaluate universal molecular parameters entering the expressions for various optically induced birefringences in chiral fluids. For this, we use the single and double excitation coupled cluster (CCSD) theory together with Dunning's augmented correlation consistent polarized basis sets of increasing size. As this is the first time these parameters are evaluated for chiral molecules using the CCSD approach, we choose possibly small test systems: a model asymmetric methane molecule, and (R)-fluoro-oxirane. With this choice, the convergence of the molecular parameters with the increase of the basis set size is investigated in detail. The results are compared to those obtained with the LPol-n (n = ds, dl, fs) and the ORP basis sets, and to the corresponding Density Functional Theory (DFT) counterparts. We can conclude that the DFT medium constant values are considerably far from coupled cluster, and therefore, aware of the known excellent performance of the CCSD method in the evaluation of various dynamic responses, we do not recommend the former methodology for accurate evaluation of the present properties. Regarding basis set convergence, the performace of the LPol-ds basis set is more efficient than that of the d-aug-cc-pVDZ set, and therefore, the former basis set can be a good choice when dealing with the study of larger systems.

Comparison of Property-Oriented Basis Sets for the Computation of Electronic and Nuclear Relaxation Hyperpolarizabilities

In the present work, we perform an assessment of several property-oriented atomic basis sets in computing (hyper)polarizabilities with a focus on the vibrational contributions. Our analysis encompasses the Pol and LPol-ds basis sets of Sadlej and co-workers, the def2-SVPD and def2-TZVPD basis sets of Rappoport and Furche, and the ORP basis set of Baranowska-Łączkowska and Łączkowski. Additionally, we use the d-aug-cc-pVQZ and aug-cc-pVTZ basis sets of Dunning and co-workers to determine the reference estimates of the investigated electric properties for small- and medium-sized molecules, respectively. We combine these basis sets with ab initio post-Hartree-Fock quantum-chemistry approaches (including the coupled cluster method) to calculate electronic and nuclear relaxation (hyper)polarizabilities of carbon dioxide, formaldehyde, cis-diazene, and a medium-sized Schiff base. The primary finding of our study is that, among all studied property-oriented basis sets, only the def2-TZVPD and ORP basis sets yield nuclear relaxation (hyper)polarizabilities of small molecules with average absolute errors less than 5.5%. A similar accuracy for the nuclear relaxation (hyper)polarizabilites of the studied systems can also be reached using the aug-cc-pVDZ basis set (5.3%), although for more accurate calculations of vibrational contributions, i.e., average absolute errors less than 1%, the aug-cc-pVTZ basis set is recommended. It was also demonstrated that anharmonic contributions to first and second hyperpolarizabilities of a medium-sized Schiff base are particularly difficult to accurately predict at the correlated level using property-oriented basis sets. For instance, the value of the nuclear relaxation first hyperpolarizability computed at the MP2/def2-TZVPD level of theory is roughly 3 times larger than that determined using the aug-cc-pVTZ basis set. We link the failure of the def2-TZVPD basis set with the difficulties in predicting the first-order field-induced coordinates. On the other hand, the aug-cc-pVDZ and ORP basis sets overestimate the property in question only by roughly 30%. In this study, we also propose a low-cost composite treatment of anharmonicity that relies on the combination of two basis sets, i.e., a large-sized basis set is employed to determine lowest-order derivatives with respect to the field-induced coordinates, and a medium-sized basis set is used to compute the higher-order derivatives. The results of calculations performed at the MP2 level of theory demonstrate that this approximate scheme is very successful at predicting nuclear relaxation hyperpolarizabilities.

On the performance of long-range-corrected density functional theory and reduced-size polarized LPol-n basis sets in computations of electric dipole (hyper)polarizabilities of π-conjugated molecules

Static longitudinal electric dipole (hyper)polarizabilities are calculated for six medium-sized π-conjugated organic molecules using recently developed LPol-n basis set family to assess their performance. Dunning's correlation-consistent basis sets of triple-ζ quality combined with MP2 method and supported by CCSD(T)/aug-cc-pVDZ results are used to obtain the reference values of analyzed properties. The same reference is used to analyze (hyper)polarizabilities predicted by selected exchange-correlation functionals, particularly those asymptotically corrected.