Chiroptical properties from time-dependent density functional theory. I. Circular dichroism spectra of organic molecules

Abstract

We report the implementation of the computation of rotatory strengths, based on time-dependent density functional theory, within the Amsterdam Density Functional program. The code is applied to the simulation of circular dichroism spectra of small and moderately sized organic molecules, such as oxiranes, aziridines, cyclohexanone derivatives, and helicenes. Results agree favorably with experimental data, and with theoretical results for molecules that have been previously investigated by other authors. The efficient algorithms allow for the simulation of CD spectra of rather large molecules at a reasonable accuracy based on first-principles theory. The choice of the Kohn-Sham potential is a critical issue. It is found that standard gradient corrected functionals often yield the correct shape of the spectrum, but the computed excitation energies are systematically underestimated for the samples being studied. The recently developed exchange-correlation potentials ''GRAC'' and ''SAOP'' often yield much better agreement here with experiments for the excitation energies. The rotatory strengths of individual transitions are usually improved by these potentials as well.

Chiroptical properties from time-dependent density functional theory. II. Optical rotations of small to medium sized organic molecules

“…18 Likewise, we have recently demonstrated that in the case of the computation of rotatory strengths the gauge dependence of the results is only very minor in case high quality basis sets including diffuse functions were employed. 14 Comparison with experimental data clearly indicates that reliable results for chiroptical properties are only obtained with such high quality basis sets in which case the gauge dependence is not very pronounced. The computation of chiroptical observables, given as total molecular properties, is very much unlike the case of NMR chemical shifts where extremely sensitive gauge dependent properties of different atoms within a molecule are evaluated and for which a gauge independent formalism is therefore vital.…”

“…We have previously found that SAOP yields improved results for individual rotatory strengths of selected molecules. 14 The SIC functional has been successfully applied by us 28 to NMR chemical shifts ͑and, somewhat less satisfactory, to nuclear spin-spin coupling constants͒. Therefore we might expect it to offer some improvements in the case of optical rotations as well, at least in some difficult cases, since they also represent a perturbation caused by an external magnetic field.…”

“…For these molecules, we have further omitted computations with the basis set Vd. For our previous work 14 we have computed the CD spectrum of hexahelicene with both the IV and Vd bases and could not observe any significant differences. The helicenes have very intense low lying CD transitions that dominate also their optical rotations.…”

“…Not surprisingly therefore, there has been recently an increasing interest in the computation of optical activity related observables by timedependent density functional theory [9][10][11] ͑TDDFT͒. For example, TDDFT implementations for electronic circular dichroism have been presented by Furche et al 12,13 in 2000 and by Autschbach et al 14 in 2002. Vibrational circular dichroism ͑VCD͒ has already been implemented for DFT by Stephens et al in 1996.…”

Ternary thiophene–X–thiophene semiconductor building blocks (X=fluorene, carbazole, phenothiazine): Modulating electronic properties and electropolymerization ability by tuning the X core

“…The excitation analysis had been performed by means of Time Dependent Density Functional Theory (TD-DFT) [53][54][55]; calculations were carried out based on geometries optimized by means ADF with the previously described method. For each excitation, the composition of the solution vector of the TD-DFT eigenvalue problem from which the transition dipole moments are computed [56][57][58] in terms of contributions from pairs of occupied and virtual MOs allows a convenient and intuitive analysis of the results in terms of "excitations" from occupied to virtual Kohn-Sham orbitals [59]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 7 We applied the Davidson iterative procedure for the computation of the eigenvalues and the eigenvectors of the TDDFT equation [60].The parameterizations adopted in the excitation analysis and in the theoretical prediction of the UV/Vis spectra are listed in Appendix B.…”