Difficulties of density functional theory in predicting the torsional potential of 2,2?-bithiophene

Abstract

ABSTRACT:The internal rotation of 2,2Ј-bithiophene was investigated within the Ž . density functional theory DFT approach. Fully optimized DFT torsional potentials are Ž . compared with Møller᎐Plesset MP2 results which predict a fourfold potential with s-cis-and s-trans-gauche minima. DFT calculations fail in describing the energetics of the internal rotation because they favor planar vs. perpendicular conformers. Gradientcorrected functionals provide torsional potentials where the gauche minima have almost vanished and the s-cis l s-trans interconversion barriers are twice as high as the barriers obtained at the MP2 level. The use of local functionals augments the shortcomings of the DFT approach. The gauche minima completely disappear and the rotational barriers are now about three times higher than the MP2 barriers. As an efficient computational approach, we suggest having geometries optimized at the DFT level and conformational energies evaluated via single-point MP2 calculations. The fitting of MP2rrDFT energies to truncated Fourier expansions allows one to predict the torsional angles and the relative energies of the critical points of the rotational potential with an accuracy similar to that afforded by MP2 calculations including full geometry optimization.

Theoretical study of the effect of ethynyl group on the structure and electrical properties of phenyl-thiadiazole systems as precursors of electron-conducting materials

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Electronic Structure and Charge Transport Properties of a Series of 3,6-(Diphenyl)-s-tetrazine Derivatives: Are They Suitable Candidates for Molecular Electronics?

“…60,61 Semiconducting related properties (E LUMO , EA, λ i and t 12 ) were calculated at the B3LYP/6-31+G* level of theory. Although Koopman's theorem is not rigorously applicable to Kohn-Sham orbital energies, Perdew proved a connection between ionization potentials/electron affinities and HOMO/LUMO energies through Janak's theorem (see, e.g.…”

Optoelectronic and nonlinear optical properties of triarylamine helicenes: a DFT study

“…The excited state characteristics (exCitation energies, transition dipole integral, rotatory strengths) were determined using adiabatic approximation using a time-dependent density functional approach (TDDFT) [68] employing the B3PW91fuctional and 6-311++ G(2d,2p) basis set. The computational cost of TDDFT is roughly comparable to singleexcitation theories based on a HF ground state, such as singleexcitation configuration interaction (CIS); however, numerical applications reported so far indicate that TDDFT employing current exchange-correlation functional performs significantly better than HF-based single-excitation theories for the low-lying valence excited states of both closed shell and open-shell molecules [69][70][71][72].…”

“…The total static dipole moment (μ), average linear polarizability (α) and first-order hyperpolarizability (β) using the x, y, z components of the compound from Gaussian 03 W [60] output were calculated by Eqs. 4-6 [61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77].…”