Is the choice of a standard zeroth‐order hamiltonian in CASPT2 ansatz optimal in calculations of excitation energies in protonated and unprotonated schiff bases of retinal?

Wolański, Łukasz; Grabarek, Dawid; Andruniów, Tadeusz

doi:10.1002/jcc.25217

Cited by 3 publications

(1 citation statement)

References 80 publications

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“…The so‐called ionization potential electron affinity (IPEA) shift, a single parameter whose numerical value (0.25 au) was selected from benchmark calculations, was supposed to be systematically used from then on . More recently, discussions about the use of IPEA, and its specific numerical value, have appeared in the literature, concerning organic systems in general, iron compounds, and free‐based and regular porphyrins in particular. In the present work, calculations with and without the use of the IPEA shift are compared.…”

Section: Introductionmentioning

confidence: 99%

RASPT2 study of the valence excited states of an iron–porphyrin–carbonyl model complex

Amor

Heitz

2019

J Comput Chem

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Multireference wavefunction calculations of the singlet valence excited states of an iron–porphyrin–pyrazine–carbonyl complex up to the Soret band (about 3 eV) are presented. This complex is chosen to be a model for the active site of carboxyhemoglobin/carboxymyoglobin. The investigations are performed at the restricted active space second‐order perturbation (RASPT2) level involving an extended active space on the porphyrin ligand in addition to the active orbitals needed for the description of the metal–ligand interactions. Metal‐to‐ligand‐charge‐transfer states d → π* and some metal‐centered d → d transitions are found in the lowest part of the spectrum, below the first π → π* intraporphyrin transitions (Q band). Doubly excited states involving simultaneous intraporphyrin and metal‐centered excitations are found in the vicinity of the second set of intraporphyrin transitions (the so‐called Soret band). The effect of the extension of the active space on the porphyrin ligand beyond the Gouterman's orbitals set is investigated together with the effect of inclusion of the ionization potential electron affinity shift in the RASPT2 treatment. © 2019 Wiley Periodicals, Inc.

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Section: Introductionmentioning

confidence: 99%

RASPT2 study of the valence excited states of an iron–porphyrin–carbonyl model complex

Amor

Heitz

2019

J Comput Chem

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The lowest singlet states of hexatriene revisited

Guareschi,

Angeli

2023

Theor Chem Acc

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The two lowest excited singlet states of trans-hexatriene and cis-hexatriene are studied by multireference perturbation theory approaches (NEVPT2 and CASPT2) in their quasi-degenerate version (QD-NEVPT2 and MS-CASPT2). For these states, we report spectroscopic properties such as the vertical and adiabatic excitation energies, some features of the topology of the potential energy surfaces (PES), and the emission energies. The theoretical vertical excitation energies for the $${2{\hspace{0.05cm}}{^1\textrm{A}_g^-}}$$ 2 1 A g - and $${1{\hspace{0.05cm}}{^1\textrm{B}_u^+}}$$ 1 1 B u + states of trans-hexatriene are found to be almost degenerate, with a value, $$\simeq$$ ≃ 5.5–5.6 eV, higher than that normally accepted in the literature, 5.2 eV and 5.1 eV, respectively. The $${2{\hspace{0.05cm}}{^1\textrm{A}_1}}$$ 2 1 A 1 and $${1{\hspace{0.05cm}}{^1\textrm{B}_2}}$$ 1 1 B 2 states of cis-hexatriene are also almost degenerate and are estimated to be at $$\simeq$$ ≃ 5.4–5.5 and $$\simeq$$ ≃ 5.5 eV, respectively, again higher than the accepted values. The adiabatic excitation energies to the $${2{\hspace{0.05cm}}{^1\textrm{A}_g^-}}$$ 2 1 A g - and $${2{\hspace{0.05cm}}{^1\textrm{A}_1}}$$ 2 1 A 1 states can be observed experimentally (in particular for the cis isomer), and our results are in excellent agreement with the experimental values. On the contrary, the vertical excitation energies for these states are not directly observable in the experimental spectra and the “experimental” values are obtained by educated guesses. We show that the hypotheses underlying these guesses are not entirely grounded.

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Quadripartite bond length rule applied to two prototypical aromatic and antiaromatic molecules

Wolański

Grochala

2023

J Mol Model

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Context In 2000, a remarkably simple relationship was introduced, which connected the calculated geometries of isomolecular states of three different multiplicities. These encompass a ground single state, the first excited triplet state, as well as related radical anion and radical cation. The rule allows the prediction of the geometry of one of the species if the three remaining ones are known. Here, we verify the applicability of this bond length rule for two small planar cyclic organic molecules, i.e., benzene and cyclobutadiene, which stand as prototypical examples of, respectively, aromatic and antiaromatic systems. We see that the rule works fairly well to benzene, and it works independently for quinoid as well as for anti-quinoid minima, despite the fact that radical anion species poses challenges for correct theoretical description. Methods To obtain chosen electronic state equilibrium geometries, three types of computational approaches were utilized: fast and efficient density functional theory DFT, the coupled cluster method CC2, the complete active space self-consistent field (CASSCF) approach, and the most accurate but also resource-consuming perturbation theory with multireference wavefunction (CASPT2) with a default value and without IPEA-shift. Dunning and co-workers correlation-consistent basis sets (aug-)cc-pVXZ (X = D, T, Q) were employed. Gaussian 16 revision A.03, Turbomole 7.1, and Molcas 8.0 computational software were used.

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Is the choice of a standard zeroth‐order hamiltonian in CASPT2 ansatz optimal in calculations of excitation energies in protonated and unprotonated schiff bases of retinal?

Cited by 3 publications

References 80 publications

RASPT2 study of the valence excited states of an iron–porphyrin–carbonyl model complex

RASPT2 study of the valence excited states of an iron–porphyrin–carbonyl model complex

The lowest singlet states of hexatriene revisited

Quadripartite bond length rule applied to two prototypical aromatic and antiaromatic molecules

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