High level theoretical study of the structure and rotational barriers of trans-stilbene

Abstract

The relative energies of stationary points on the potential energy surface of trans-stilbene have been accurately determined using Hartree–Fock, second and third-order Møller–Plesset (MP2, MP3), as well as Coupled Clusters theories with single and double excitations (CCSD), together with a perturbative estimate of connected triple excitations [CCSD(T)], in conjunction with basis sets of increasing size, containing up to 1130 basis functions. A focal point analysis has been carried out in order to determine how the energy differences and rotational barriers approach convergence, enabling extrapolation of the CCSD(T) results to a near-complete basis set. The investigated saddle points pertain to independent rotations of the phenyl rings about the single C–C bond, and to pedalling motions described by a twofold rotation of the central ethylene bond about the longitudinal axis of the molecule. The benchmark calculations presented in this study lead to the conclusion that, in the nonrelativistic limit and within the frozen core approximation, trans-stilbene in vacuum is a strictly planar molecule in its absolute energy minimum form, in sharp contrast with many previous theoretical studies. This point has been ultimately confirmed by an MP2 geometry optimization using the aug-cc-pVDZ basis set. At last, the energy of cis-stilbene relative to the trans-isomer is accurately evaluated.

Study of the photoelectron and electron momentum spectra of cyclopentene using benchmark Dyson orbital theories

“…Functional Theory and various many-body approaches up to the confines of non-relativistic quantum mechanics [89]. The obtained puckering angle (19.4º) presented in this work compares nonetheless more than favorably (3º error only) with the results of most experimental structural determinations.…”

Ab Initio Static and Molecular Dynamics Study of 4‐Styrylpyridine

“…However, the analysis of the resolved rotational structure in the fluorescence spectrum of trans-stilbene-recorded on an ultra-cold (6 K), collision-free molecular beam-demonstrates that this species is strictly planar in vacuum and in its ground-state vibronic level. [69] Such an experiment has not been carried out so far for trans-4-sty-A C H T U N G T R E N N U N G rylpyridine, but from the theoretical point of view, [70] it is known that the HF and MP2 methods give nonplanar geometries for trans-stilbene whereas the DFT methods give strictly planar geometries (which is in perfect agreement with experiment). Therefore, given the superior performance shown by the DFT methods, we can assert on the basis of our DFT results that trans-4-styrylpyridine is also strictly planar in vacuum and in the limit T!0 K.…”

Photoisomerization of Stilbene: A Spin-Flip Density Functional Theory Approach

“…The planarity of trans-stilbene, however, has been a source of controversy. 104,105 The SA-2-CAS(2,2) geometry optimization leads to a nonplanar structure whose phenyl groups rotate out of the molecular plane. 47 In the conventional DFT method with the B3LYP functional, calculations with the 6-31G(d) and cc-pVDZ basis sets give a planar conformation for the trans isomer, 50,106 while recent computations with the 6-31G(d,p), 6-311G(d,p), and 6-311þG(2d,p) basis sets predict a nonplanar geometry.…”

“…CCSD(T) (coupled cluster single and double excitations with perturbative triple excitations) calculations with an extrapolation to the complete basis set limit have predicted that the energy difference is 0.3 kcal/mol in favor of the planar form. 105 The cis isomer, (S 0 ) cis , has an approximately C 2 geometry. The cis -C 2 C 1 C 8 and -C 1 C 8 C 9 bond angles increase by 4°with respect to the trans isomer.…”