Performance of Multilevel Methods for Excited States

J. Chem. Theory Comput.

Tajti

et al. 2023

Self Cite

While Coupled-Cluster methods have been proven to provide an accurate description of excited electronic states, the scaling of the computational costs with the system size limits the degree for which these methods can be applied. In this work different aspects of fragment-based approaches are studied on noncovalently bound molecular complexes with interacting chromophores of the fragments, such as π-stacked nucleobases. The interaction of the fragments is considered at two distinct steps. First, the states localized on the fragments are described in the presence of the other fragment(s); for this we test two approaches. One method is founded on QM/MM principles, only including the electrostatic interaction between the fragments in the electronic structure calculation with Pauli repulsion and dispersion effects added separately. The other model, a Projection-based Embedding (PbE) using the Huzinaga equation, includes both electrostatic and Pauli repulsion and only needs to be augmented by dispersion interactions. In both schemes the extended Effective Fragment Potential (EFP2) method of Gordon et al. was found to provide an adequate correction for the missing terms. In the second step, the interaction of the localized chromophores is modeled for a proper description of the excitonic coupling. Here the inclusion of purely electrostatic contributions appears to be sufficient: it is found that the Coulomb part of the coupling provides accurate splitting of the energies of interacting chromophores that are separated by more than 4 Å.

Section: Methodologies For Modeling Intermolecular Interactions In Ex...mentioning

confidence: 99%

Benchmarking Aspects of Ab Initio Fragment Models for Accurate Excimer Potential Energy Surfaces

J. Chem. Theory Comput.

Tajti

et al. 2023

Self Cite

“…This expression is often used in QM/MM and other embedding schemes, we also have tested it in Ref. 25. The quality of this approximation depends on the electronic structure method, as well as on the choice of V ef f i and ∆V i and will be discussed in Subsection 2.1 in detail.…”

Section: Methodologies Of Modeling Intermolecular Interactions In Exc...mentioning

confidence: 99%

“…Parravicini and Jagau 40 studied ionization, electron attachment and electronic resonances; also applying the concentric virtual orbital localization scheme. 41 A benchmark study by Hégely et al 42 compared various multilevel approaches including PbE for the calculation of excitation energies.…”

Section: Huzinaga Embedding Schemementioning

confidence: 99%

Definition and benchmarking of ab initio fragment methods for accurate excimer potential energy surfaces

Stanton

et al. 2023

Preprint

While Coupled-Cluster methods have been proven to provide an accurate description of excited electronic states, the scaling of the computational costs with the system size limits their applicability. In this study a fragment-based approach is presented which can be applied to non-covalently bound molecules with interacting chromophores localized on the fragments (so called Frankel pairs), such as $\pi$-stacked nucleobases. The interaction of the fragments is considered at two distinct points. First, the states localized on the fragments are described in the presence of the other fragment(s), for which we test two approaches. A QM/MM type method that only includes the electrostatic interaction between the fragments in the electronic structure calculations, while Pauli repulsion and dispersion effects are added separately. The other model, a Projection-based Embedding (PbE) using the Huzinaga equation includes both electrostatic and Pauli repulsion and only needs to be augmented by dispersion interactions. In both schemes the extended Effective Fragment Potential (EFP2) method of Gordon et al.~was found to provide an accurate correction for the missing terms. In the second step, the interaction of the localized chromophores is modeled for a proper description of the excitonic coupling. Here the inclusion of purely electrostatic contributions appears to be sufficient: it is found that the Coulomb part of the coupling, as evaluated using the Transition Density Cube method, provides accurate splitting of the energy of interacting chromophores above 4 \AA\ intermolecular separations.

“…This expression is often used in QM/MM and other embedding schemes; we also have tested it in Ref. 30. The quality of this approximation depends on the electronic structure method used, as well as upon the choice of V ef f i and ∆V i ; this will be discussed in detail in Subsection 2.1.…”

Section: Methodologies For Modeling Intermolecular Interactions In Ex...mentioning

confidence: 99%

“…The orbitals obtained this way can be used in correlated wavefunction (WF) calculations for both ground and excited states. 30 The energy ansatz of this method for WF-in-DFT embedding is…”

Section: Huzinaga Embedding Schemementioning

confidence: 99%

Definition and benchmarking of ab initio fragment methods for accurate excimer potential energy surfaces

Stanton

et al. 2023

Preprint

While Coupled-Cluster methods have been proven to provide an accurate description of excited electronic states, the scaling of the computational costs with the system size limits the degree for which these methods can be applied. In this study a fragment-based approach is presented for non-covalently bound molecular complexes with interacting chromophores of the fragments (so called Frenkel pairs), such as pi-stacked nucleobases. The interaction of the fragments is considered at two distinct steps. First, the states localized on the fragments are described in the presence of the other fragment(s); for this we test two approaches. One method is founded on QM/MM principles, only including the electrostatic interaction between the fragments in the electronic structure calculation with Pauli repulsion and dispersion effects added separately. The other model, a Projection-based Embedding (PbE) using the Huzinaga equation includes both electrostatic and Pauli repulsion and only needs to be augmented by dispersion interactions. In both schemes the extended Effective Fragment Potential (EFP2) method of Gordon et al. was found to provide an adequate correction for the missing terms. In the second step, the interaction of the localized chromophores is modeled for a proper description of the excitonic coupling. Here the inclusion of purely electrostatic contributions appears to be sufficient: it is found that the Coulomb part of the coupling, as evaluated by the transition density cube method, provides accurate splitting of the energies of interacting chromophores that are separated by more than 4 Angstrom.