Taming the excited states of butadiene, hexatriene, and octatetraene using state specific multireference perturbation theory with density functional theory orbitals

Abstract

To compute the electronic excitation energies, a state-specific multireference Møller–Plesset perturbation theory (SSMRPT) with a complete active space configuration interaction reference function constructed using the orbitals obtained by the density functional theory (DFT) is presented as an accurate, as well as computationally affordable, and efficient protocol at the level of second order. The global hybrid B3LYP (Becke, 3-parameter, Lee–Yang–Parr) functional has been used to generate orbitals. The present method, called DFT-SSMRPT, uses perturbers that are individual Slater determinants and accounts for the coupling between the nondynamical and dynamical correlation effects. We have applied the new method to compute excitation energies in conjugated systems of π-electrons such as trans-1,3-butadiene, trans,trans-1,3,5-hexatriene, and all-trans-1,3,5,7-octatetraene. The ordering of the excited states is correctly reproduced by the DFT-SSMRPT calculations. The relative ordering of low-lying excited 1Bu and 1Ag states alters when the length of the polyene changes. The results match reasonably well with the literature including experimental and best theoretical findings. The accuracy of the method is sufficient to discern the energy gap between the close low-lying singlet and triplet states. The DFT-SSMRPT appears as an affordable computational ab initio avenue for a qualitatively correct description of excitation energies.

Description of the Methylene Amidogene Radical and Its Anion with an Economical Treatment of Correlation Effects Using Density Functional Theory Orbitals

“…The estimates provided by the DFT-CASCI and CASSCF methods are practically identical . The method produces bond lengths, angles, and normal-mode frequencies that are in agreement with the commonly used approaches.…”

“…In light of this end, we revisit the electronic structural properties of the ground and low-lying excited states (X ̃2B 2 , A ̃2B 1 , and B ̃2A 1 ) of the neutral radical H 2 CN by our recently suggested state-specific multireference perturbation theory (SSMRPT) procedure with density functional theory orbitals (DFT-SSMRPT). 26 The DFT-SSMRPT method (a secondorder Rayleigh−Schrodinger perturbation theory) is designed to deal with multireference (MR)/multiconfigurational (MC) or strongly correlated systems problems, since it is particularly efficient for capturing various electronic correlation effects in a systematic, balanced, and accurate manner. Geometries, harmonic vibrational frequencies, dissociation surfaces, and excitation energies for the electronic states of H 2 CN have been computed and analyzed in the present work.…”

Theory, implementation, and disappointing results for two-photon absorption cross sections within the doubly electron-attached equation-of-motion coupled-cluster framework

“…Prototypical polyenes such as butadiene, hexatriene, and octatetraene feature close-lying excited states with multiconfigurational (mixed Rydberg and doubly excited) wave functions [14][15][16][17] . These systems, therefore, represent challenging cases that give a measure of the balance of dynamical and static correlation captured by a multireference method in the description of these excited-state energies and wave functions.…”

“…The theoretical treatment of diradical electronic structure requires sophisticated methods that can provide a balanced treatment of the static and dynamical electronic correlation. Further, accurate modeling of the excitation-energy spectra of prototypical polyenes (e.g., trans-butadiene, transhexatriene, trans-octatetraene) is notoriously difficult due to the presence of low-lying states with multiconfigurational character [9][10][11][12][13][14][15][16][17] . For example, the 2A g singlet in trans-butadiene has contributions from both the Rydberg excitations and doubly excited configurations relative to its ground state, which requires methods that can describe these contributions in a balanced fashion.…”

Full-frequency dynamical Bethe-Salpeter equation without frequency and a study of double excitations

“…As an example, we have studied the 2 1 A g excitation of butadiene, hexatriene, and octatetraene, which is known to have substantial double excitation character. 24,33,[39][40][41][42][43] Table I provides our GW/BSE@HF excitation energies and the percentage contribution of doubles excitations (%R 2 ) to the eigenvector. We also list theoretical best estimates ("TBE-1") 35 and literature values from strict and extended ADC(2), EOM-CCSD, and ADC(3) methods.…”