Toward an Accurate Ab Initio Description of Low-Lying Singlet Excited States of Polyenesстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 17 августа 2021 г.
Аннотация:Low-lying excited states of carotenoids play a crucial role in many important biophysical processes such as photosynthesis. Most of these excited states are strongly correlated which both makes them challenging for a qualitative ab initio description
and an engaging model system for trying out emerging multireference methods. Among these methods, driven similarity renormalization group (DSRG) and its perturbative version (DSRG-MRPT2) are especially attractive in terms of both accuracy and moderate numerical complexity. In this paper, we applied density matrix renormalization group (DMRG) followed by DSRG-MRPT2 for a calculation of vertical and adiabatic excitation energies into the 2Ag-, 1Bu−, and 1Bu+ electronic states of polyenes containing
from 8 to 13 conjugating double bonds acting as a model for natural carotenoids. It was shown that the DSRG flow parameter should be adjusted to ensure both the energy convergence with respect to it and the agreement with the experimental data. With the
increased flow parameter, the proposed combination of methods provides a reasonable agreement with experiment. The deviations of the adiabatic excitation energies are less than 1000 cm−1 for the 2Ag- and less than 3000 cm−1 for the excited states of the Bu symmetry which in terms of accuracy significantly outperforms N-electron valence
state perturbation theory (NEVPT2). At the same time, DSRG-MRPT2 is shown to be robust with respect to variation of quality of the DMRG reference wavefunction such as the orbital optimization or the number of electronic states in the averaging.