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Rodney J Bartlett - One of the best experts on this subject based on the ideXlab platform.
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similarity Transformed Equation of motion coupled cluster singles and doubles method with spin orbit effects for excited states
Journal of Chemical Physics, 2019Co-Authors: Denis Bokhan, D N Trubnikov, Ajith Perera, Rodney J BartlettAbstract:The similarity Transformed Equation-of-motion coupled-cluster method (STEOM-CCSD) for excited states is extended to treat spin-orbit coupling interactions (SOIs) using the spin-orbit mean field approximation of the Breit-Pauli Hamiltonian. Two possible schemes to include the spin-orbit splittings of excited states within the STEOM-CCSD model are formulated. They are identified as “diagonalize-then-perturb” and “perturb-then-diagonalize” approaches. The second approach is more suited for cases where SOI is larger, and the first approach breaks down. With the aid of the standard many-body diagrammatic techniques, expressions for all the necessary matrix elements can be derived. These new formulations are implemented in the ACES III suite of parallel coupled cluster programs, and benchmark studies are performed. Numerical tests for several atoms and molecules show a good agreement of calculated spin-orbit splittings to experiment, while also documenting the numerical differences between the two approaches.
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similarity Transformed Equation of motion coupled cluster singles and doubles method with spin orbit effects for excited states
Journal of Chemical Physics, 2019Co-Authors: Denis Bokhan, D N Trubnikov, Ajith Perera, Rodney J BartlettAbstract:The similarity Transformed Equation-of-motion coupled-cluster method (STEOM-CCSD) for excited states is extended to treat spin-orbit coupling interactions (SOIs) using the spin-orbit mean field approximation of the Breit-Pauli Hamiltonian. Two possible schemes to include the spin-orbit splittings of excited states within the STEOM-CCSD model are formulated. They are identified as “diagonalize-then-perturb” and “perturb-then-diagonalize” approaches. The second approach is more suited for cases where SOI is larger, and the first approach breaks down. With the aid of the standard many-body diagrammatic techniques, expressions for all the necessary matrix elements can be derived. These new formulations are implemented in the ACES III suite of parallel coupled cluster programs, and benchmark studies are performed. Numerical tests for several atoms and molecules show a good agreement of calculated spin-orbit splittings to experiment, while also documenting the numerical differences between the two approaches.The similarity Transformed Equation-of-motion coupled-cluster method (STEOM-CCSD) for excited states is extended to treat spin-orbit coupling interactions (SOIs) using the spin-orbit mean field approximation of the Breit-Pauli Hamiltonian. Two possible schemes to include the spin-orbit splittings of excited states within the STEOM-CCSD model are formulated. They are identified as “diagonalize-then-perturb” and “perturb-then-diagonalize” approaches. The second approach is more suited for cases where SOI is larger, and the first approach breaks down. With the aid of the standard many-body diagrammatic techniques, expressions for all the necessary matrix elements can be derived. These new formulations are implemented in the ACES III suite of parallel coupled cluster programs, and benchmark studies are performed. Numerical tests for several atoms and molecules show a good agreement of calculated spin-orbit splittings to experiment, while also documenting the numerical differences between the two approaches.
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explicitly correlated similarity Transformed Equation of motion coupled cluster method
Journal of Chemical Physics, 2015Co-Authors: Denis Bokhan, D N Trubnikov, Rodney J BartlettAbstract:Similarity Transformed Equation-of-motion method, based on linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] model, has been formulated and implemented. An extension of similarity transformation operator is introduced in order to treat short-range correlation effects for excited states. Additionally, effective reduction of the number of active virtuals can be obtained by such modification. Numerical tests for sets of valence and Rydberg excited states of several molecules are conducted. Statistical measures of errors in excitation energies show that explicitly correlated results are accurate up to 0.1 e.V already at a double-ζ level compared to those in the complete basis set limit, if the excitation energy is not too close to an ionization threshold. An example of long-range charge transfer excitation is also considered and highly accurate results are obtained.
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ab initio simulation of uv vis absorption spectra for atmospheric modeling method design for medium sized molecules
Physical Chemistry Chemical Physics, 2010Co-Authors: Anna Melnichuk, Ajith Perera, Rodney J BartlettAbstract:A procedure is presented to obtain accurate absorption cross-sections for dissociative excited states. The focus is the ability to approximate many vibrational degrees of freedom while maintaining a minimal computational time. The vibrational Hamiltonian for bound and unbound surfaces is solved within a discrete variable representation (DVR) framework. Properties and energies of excited states are computed using electron correlated singles and doubles Equation-of-motion (EOM-CCSD) and similarity Transformed Equation-of-motion (STEOM-CCSD) methods as implemented in ACESII. The novelty of this procedure is that it is designed to work for medium-sized molecules (size limited by the choice of electronic structure method, not vibrational degrees of freedom) with one or more photodissociation pathways. The theoretical absorption cross-section of NaOH is presented as a small-scale example.
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gradients for the similarity Transformed Equation of motion coupled cluster method
Journal of Chemical Physics, 1999Co-Authors: Steven R Gwaltney, Rodney J Bartlett, Marcel NooijenAbstract:A derivation of gradients for the similarity Transformed Equation-of-motion coupled-cluster singles and doubles method is presented. Algebraic operator Equations for all of the terms which appear in the Equations are given, with a discussion about the procedure for solving the Equations.
Marcel Nooijen - One of the best experts on this subject based on the ideXlab platform.
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similarity Transformed Equation of motion vibrational coupled cluster theory
Journal of Chemical Physics, 2018Co-Authors: Jacob A Faucheaux, Marcel Nooijen, So HirataAbstract:A similarity-Transformed Equation-of-motion vibrational coupled-cluster (STEOM-XVCC) method is introduced as a one-mode theory with an effective vibrational Hamiltonian, which is similarity Transformed twice so that its lower-order operators are dressed with higher-order anharmonic effects. The first transformation uses an exponential excitation operator, defining the Equation-of-motion vibrational coupled-cluster (EOM-XVCC) method, and the second uses an exponential excitation-deexcitation operator. From diagonalization of this doubly similarity-Transformed Hamiltonian in the small one-mode excitation space, the method simultaneously computes accurate anharmonic vibrational frequencies of all fundamentals, which have unique significance in vibrational analyses. We establish a diagrammatic method of deriving the working Equations of STEOM-XVCC and prove their connectedness and thus size-consistency as well as the exact equality of its frequencies with the corresponding roots of EOM-XVCC. We furthermore el...
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exploring the accuracy of a low scaling similarity Transformed Equation of motion method for vertical excitation energies
Journal of Chemical Theory and Computation, 2018Co-Authors: Achintya Kumar Dutta, Frank Neese, Marcel Nooijen, Robert IzsakAbstract:The newly developed back Transformed pair natural orbital based similarity Transformed Equation of motion (bt-STEOM) method at the coupled cluster singles and doubles level (CCSD) is combined with an appropriate modification of our earlier active space selection scheme for STEOM. The resulting method is benchmarked for valence, Rydberg, and charge transfer excited states of Thiel’s test set and other test systems. The bt-PNO-STEOM-CCSD method gives very similar results to canonical STEOM-CCSD for both singlet and triplet excited states. It performs in a balanced manner for all these types of excited states, while the EOM-CCSD method performs especially well for Rydberg excited states and the CC2 method excels at obtaining accurate results for valence excited states. Both EOM-CCSD and CC2 perform worse than bt-PNO-STEOM-CCSD for charge transfer states for the test cases studied.
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similarity Transformed Equation of motion coupled cluster theory revisited a benchmark study of valence excited states
Molecular Physics, 2014Co-Authors: John Sous, Prateek Goel, Marcel NooijenAbstract:The similarity Transformed Equation of motion coupled cluster (STEOM-CC) method is benchmarked against CC3 and EOM-CCSDT-3 for a large test set of valence excited states of organic molecules studied by Schreiber et al. [M. Schreiber, M.R. Silva-Junior, S.P. Sauer, and W. Thiel, J. Chem. Phys. 128, 134110 (2008)]. STEOM-CC is found to behave quite satisfactorily and provides significant improvement over EOM-CCSD, CASPT2 and NEVPT2 for singlet excited states, lowering standard deviations of these methods by almost a factor of 2. Triplet excited states are found to be described less accurately, however. Besides the parent version of STEOM-CC, additional variations are considered. STEOM-D includes a perturbative correction from doubly excited determinants. The novel STEOM-H (ω) approach presents a sophisticated technique to render the STEOM-CC Transformed Hamiltonian hermitian. In STEOM-PT, the expensive CCSD step is replaced by many-body second-order perturbation theory (MBPT(2)), while extended STEOM (EXT-S...
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similarity Transformed Equation of motion coupled cluster theory revisited a benchmark study of valence excited states
arXiv: Chemical Physics, 2014Co-Authors: John Sous, Prateek Goel, Marcel NooijenAbstract:The similarity Transformed Equation of motion coupled cluster (STEOM-CC) method is benchmarked against CC3 and EOM-CCSDT-3 for a large test set of valence excited states of organic molecules studied by Schreiber et al. [M. Schreiber, M.R. Silva-Junior, S.P. Sauer, and W. Thiel, J. Chem. Phys. $\textbf{128}$, 134110 (2008)]. STEOM-CC is found to behave quite satisfactorily and provides significant improvement over EOM-CCSD, CASPT2 and NEVPT2 for singlet excited states, lowering standard deviations of these methods by almost a factor of 2. Triplet excited states are found to be described less accurately, however. Besides the parent version of STEOM-CC, additional variations are considered. STEOM-D includes a perturbative correction from doubly excited determinants. The novel STEOM-H ($\omega$) approach presents a sophisticated technique to render the STEOM-CC Transformed Hamiltonian hermitian. In STEOM-PT, the expensive CCSD step is replaced by many-body second-order perturbation theory (MBPT(2)), while extended STEOM (EXT-STEOM) provides access to doubly excited states. To study orbital invariance in STEOM, we investigate orbital rotation in the STEOM-ORB approach. Comparison of theses variations of STEOM for the large test set provides a comprehensive statistical basis to gauge the usefulness of these approaches.
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analytical energy gradients for excited state coupled cluster methods automated algebraic derivation of first derivatives for Equation of motion coupled cluster and similarity Transformed Equation of motion coupled cluster theories
AdQC, 2005Co-Authors: Mark Wladyslawski, Marcel NooijenAbstract:Abstract The Equation-of-motion coupled-cluster (EOM-CC) and similarity Transformed Equation-of-motion coupled-cluster (STEOM-CC) methods have been firmly established as accurate and routinely applicable extensions of single-reference coupled-cluster theory to describe electronically excited states. An overview of these methods is provided, with emphasis on the many-body similarity transform concept that is the key to a rationalization of their accuracy. The main topic of the paper is the derivation of analytical energy gradients for such non-variational electronic structure approaches, with an ultimate focus on obtaining their detailed algebraic working Equations. A general theoretical framework using Lagrange's method of undetermined multipliers is presented, and the method is applied to formulate the EOM-CC and STEOM-CC gradients in abstract operator terms, following the previous work in [P.G. Szalay, Int. J. Quantum Chem. 55 (1995) 151] and [S.R. Gwaltney, R.J. Bartlett, M. Nooijen, J. Chem. Phys. 111 (1999) 58]. Moreover, the systematics of the Lagrange multiplier approach is suitable for automation by computer, enabling the derivation of the detailed derivative Equations through a standardized and direct procedure. To this end, we have developed the SMART (Symbolic Manipulation and Regrouping of Tensors) package of automated symbolic algebra routines, written in the Mathematica programming language. The SMART toolkit provides the means to expand, differentiate, and simplify Equations by manipulation of the detailed algebraic tensor expressions directly. The Lagrangian multiplier formulation establishes a uniform strategy to perform the automated derivation in a standardized manner: A Lagrange multiplier functional is constructed from the explicit algebraic Equations that define the energy in the electronic method; the energy functional is then made fully variational with respect to all of its parameters, and the symbolic differentiations directly yield the explicit Equations for the wavefunction amplitudes, the Lagrange multipliers, and the analytical gradient via the perturbation-independent generalized Hellmann–Feynman effective density matrix. This systematic automated derivation procedure is applied to obtain the detailed gradient Equations for the excitation energy (EE-), double ionization potential (DIP-), and double electron affinity (DEA-) similarity Transformed Equation-of-motion coupled-cluster singles-and-doubles (STEOM-CCSD) methods. In addition, the derivatives of the closed-shell-reference excitation energy (EE-), ionization potential (IP-), and electron affinity (EA-) Equation-of-motion coupled-cluster singles-and-doubles (EOM-CCSD) methods are derived. Furthermore, the perturbative EOM-PT and STEOM-PT gradients are obtained. The algebraic derivative expressions for these dozen methods are all derived here uniformly through the automated Lagrange multiplier process and are expressed compactly in a chain-rule/intermediate-density formulation, which facilitates a unified modular implementation of analytic energy gradients for CCSD/PT-based electronic methods. The working Equations for these analytical gradients are presented in full detail, and their factorization and implementation into an efficient computer code are discussed.
Robert Izsak - One of the best experts on this subject based on the ideXlab platform.
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An excited state coupled-cluster study on indigo dyes
2021Co-Authors: Marvin H. Lechner, Frank Neese, Robert IzsakAbstract:In the present study, the domain-based pair natural orbital implementation of the similarity-Transformed Equation of motion method is employed to reproduce the vibrationally resolved absorption spectra of indigo dyes. After an initial investigation of multireference, basis set and implicit solvent effects, our calculated 0–0 transition energies are compared to a benchmark set of experimental absorption band maxima. It is established that the agreement between our method and experimental results is well below the desired 0.1 eV threshold in virtually all cases and that the shift in excitation energies upon chemical substitution is also well reproduced. Finally, the entire spectra of some of the main components of the Tyrian purple dye mixture are reproduced and it is found that our computed spectra match the experimental ones without an empirical shift.
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accurate computation of the absorption spectrum of chlorophyll a with pair natural orbital coupled cluster methods
Journal of Physical Chemistry B, 2020Co-Authors: Frank Neese, Abhishek Sirohiwal, Romain Berraudpache, Robert Izsak, Dimitrios A PantazisAbstract:The ability to accurately compute low-energy excited states of chlorophylls is critically important for understanding the vital roles they play in light harvesting, energy transfer, and photosynthetic charge separation. The challenge for quantum chemical methods arises both from the intrinsic complexity of the electronic structure problem and, in the case of biological models, from the need to account for protein-pigment interactions. In this work, we report electronic structure calculations of unprecedented accuracy for the low-energy excited states in the Q and B bands of chlorophyll a. This is achieved by using the newly developed domain-based local pair natural orbital (DLPNO) implementation of the similarity Transformed Equation of motion coupled cluster theory with single and double excitations (STEOM-CCSD) in combination with sufficiently large and flexible basis sets. The results of our DLPNO-STEOM-CCSD calculations are compared with more approximate approaches. The results demonstrate that, in contrast to time-dependent density functional theory, the DLPNO-STEOM-CCSD method provides a balanced performance for both absorption bands. In addition to vertical excitation energies, we have calculated the vibronic spectrum for the Q and B bands through a combination of DLPNO-STEOM-CCSD and ground-state density functional theory frequency calculations. These results serve as a basis for comparison with gas-phase experiments.
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a new density for transition properties within the similarity Transformed Equation of motion approach
Molecular Physics, 2020Co-Authors: Soumen Ghosh, Romain Berraudpache, Achintya Kumar Dutta, Bernardo De Souza, Robert IzsakAbstract:Similarity Transformed Equation of motion coupled cluster theory offers an efficient way of computing excited state energies by decoupling the space of singles from higher excitations. However, whe...
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unveiling the photophysical properties of boron dipyrromethene dyes using a new accurate excited state coupled cluster method
Journal of Chemical Theory and Computation, 2020Co-Authors: Romain Berraudpache, Frank Neese, Giovanni Bistoni, Robert IzsakAbstract:Boron-dipyrromethene (BODIPY) molecules form a class of fluorescent dyes known for their exceptional photoluminescence properties. Today, they are used extensively in various applications from fluorescent imaging to optoelectronics. The ease of altering the BODIPY core has allowed scientists to synthesize dozens of analogues by exploring chemical substitutions of various kinds or by increasing the length of conjugated groups. However, predicting the impact of any chemical change accurately is still a challenge, especially as most computational methods fail to describe correctly the photophysical properties of BODIPY derivatives. In this study, the recently developed coupled cluster method called "domain-based local pair natural orbital similarity Transformed Equation of motion-coupled cluster singles and doubles" (DLPNO-STEOM-CCSD) is employed to compute the lowest vertical excitation energies of more than 50 BODIPY molecules. The method performs remarkably well yielding an accuracy of about 0.06 eV compared to the experimental absorption maxima. We also provide an estimate to the error made by neglecting vibronic effects in the computed spectra. The dyes selected for investigation here span a large range of molecular sizes and chemical functionalities and are embedded in solvents with different polarities. We have also investigated if the method is able to correctly reproduce the impact of a single chemical modification on the absorption energy. To characterize the method in more specific terms, we have studied four large BODIPY analogues used in real-life applications due to their interesting chemical properties. These examples should illustrate the capacity of the DLPNO-STEOM-CCSD procedure to become a method of choice for the study of photophysical properties of medium to large organic compounds.
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accurate band gap predictions of semiconductors in the framework of the similarity Transformed Equation of motion coupled cluster theory
Inorganic Chemistry, 2019Co-Authors: Anneke Dittmer, Frank Neese, Robert Izsak, Dimitrios MaganasAbstract:In this work, we present a detailed comparison between wave-function-based and particle/hole techniques for the prediction of band gap energies of semiconductors. We focus on the comparison of the back-Transformed Pair Natural Orbital Similarity Transformed Equation of Motion Coupled-Cluster (bt-PNO-STEOM-CCSD) method with Time Dependent Density Functional Theory (TD-DFT) and Delta Self Consistent Field/DFT (Δ-SCF/DFT) that are employed to calculate the band gap energies in a test set of organic and inorganic semiconductors. Throughout, we have used cluster models for the calculations that were calibrated by comparing the results of the cluster calculations to periodic DFT calculations with the same functional. These calibrations were run with cluster models of increasing size until the results agreed closely with the periodic calculation. It is demonstrated that bt-PNO-STEOM-CC yields accurate results that are in better than 0.2 eV agreement with the experiment. This holds for both organic and inorganic semiconductors. The efficiency of the employed computational protocols is thoroughly discussed. Overall, we believe that this study is an important contribution that can aid future developments and applications of excited state coupled cluster methods in the field of solid-state chemistry and heterogeneous catalysis.
Frank Neese - One of the best experts on this subject based on the ideXlab platform.
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An excited state coupled-cluster study on indigo dyes
2021Co-Authors: Marvin H. Lechner, Frank Neese, Robert IzsakAbstract:In the present study, the domain-based pair natural orbital implementation of the similarity-Transformed Equation of motion method is employed to reproduce the vibrationally resolved absorption spectra of indigo dyes. After an initial investigation of multireference, basis set and implicit solvent effects, our calculated 0–0 transition energies are compared to a benchmark set of experimental absorption band maxima. It is established that the agreement between our method and experimental results is well below the desired 0.1 eV threshold in virtually all cases and that the shift in excitation energies upon chemical substitution is also well reproduced. Finally, the entire spectra of some of the main components of the Tyrian purple dye mixture are reproduced and it is found that our computed spectra match the experimental ones without an empirical shift.
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protein matrix control of reaction center excitation in photosystem ii
Journal of the American Chemical Society, 2020Co-Authors: Frank Neese, Abhishek Sirohiwal, Dimitrios A PantazisAbstract:Photosystem II (PSII) is a multisubunit pigment-protein complex that uses light-induced charge separation to power oxygenic photosynthesis. Its reaction center chromophores, where the charge transfer cascade is initiated, are arranged symmetrically along the D1 and D2 core polypeptides and comprise four chlorophyll (PD1, PD2, ChlD1, ChlD2) and two pheophytin molecules (PheoD1 and PheoD2). Evolution favored productive electron transfer only via the D1 branch, with the precise nature of primary excitation and the factors that control asymmetric charge transfer remaining under investigation. Here we present a detailed atomistic description for both. We combine large-scale simulations of membrane-embedded PSII with high-level quantum-mechanics/molecular-mechanics (QM/MM) calculations of individual and coupled reaction center chromophores to describe reaction center excited states. We employ both range-separated time-dependent density functional theory and the recently developed domain based local pair natural orbital (DLPNO) implementation of the similarity Transformed Equation of motion coupled cluster theory with single and double excitations (STEOM-CCSD), the first coupled cluster QM/MM calculations of the reaction center. We find that the protein matrix is exclusively responsible for both transverse (chlorophylls versus pheophytins) and lateral (D1 versus D2 branch) excitation asymmetry, making ChlD1 the chromophore with the lowest site energy. Multipigment calculations show that the protein matrix renders the ChlD1 → PheoD1 charge-transfer the lowest energy excitation globally within the reaction center, lower than any pigment-centered local excitation. Remarkably, no low-energy charge transfer states are located within the "special pair" PD1-PD2, which is therefore excluded as the site of initial charge separation in PSII. Finally, molecular dynamics simulations suggest that modulation of the electrostatic environment due to protein conformational flexibility enables direct excitation of low-lying charge transfer states by far-red light.
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accurate computation of the absorption spectrum of chlorophyll a with pair natural orbital coupled cluster methods
Journal of Physical Chemistry B, 2020Co-Authors: Frank Neese, Abhishek Sirohiwal, Romain Berraudpache, Robert Izsak, Dimitrios A PantazisAbstract:The ability to accurately compute low-energy excited states of chlorophylls is critically important for understanding the vital roles they play in light harvesting, energy transfer, and photosynthetic charge separation. The challenge for quantum chemical methods arises both from the intrinsic complexity of the electronic structure problem and, in the case of biological models, from the need to account for protein-pigment interactions. In this work, we report electronic structure calculations of unprecedented accuracy for the low-energy excited states in the Q and B bands of chlorophyll a. This is achieved by using the newly developed domain-based local pair natural orbital (DLPNO) implementation of the similarity Transformed Equation of motion coupled cluster theory with single and double excitations (STEOM-CCSD) in combination with sufficiently large and flexible basis sets. The results of our DLPNO-STEOM-CCSD calculations are compared with more approximate approaches. The results demonstrate that, in contrast to time-dependent density functional theory, the DLPNO-STEOM-CCSD method provides a balanced performance for both absorption bands. In addition to vertical excitation energies, we have calculated the vibronic spectrum for the Q and B bands through a combination of DLPNO-STEOM-CCSD and ground-state density functional theory frequency calculations. These results serve as a basis for comparison with gas-phase experiments.
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unveiling the photophysical properties of boron dipyrromethene dyes using a new accurate excited state coupled cluster method
Journal of Chemical Theory and Computation, 2020Co-Authors: Romain Berraudpache, Frank Neese, Giovanni Bistoni, Robert IzsakAbstract:Boron-dipyrromethene (BODIPY) molecules form a class of fluorescent dyes known for their exceptional photoluminescence properties. Today, they are used extensively in various applications from fluorescent imaging to optoelectronics. The ease of altering the BODIPY core has allowed scientists to synthesize dozens of analogues by exploring chemical substitutions of various kinds or by increasing the length of conjugated groups. However, predicting the impact of any chemical change accurately is still a challenge, especially as most computational methods fail to describe correctly the photophysical properties of BODIPY derivatives. In this study, the recently developed coupled cluster method called "domain-based local pair natural orbital similarity Transformed Equation of motion-coupled cluster singles and doubles" (DLPNO-STEOM-CCSD) is employed to compute the lowest vertical excitation energies of more than 50 BODIPY molecules. The method performs remarkably well yielding an accuracy of about 0.06 eV compared to the experimental absorption maxima. We also provide an estimate to the error made by neglecting vibronic effects in the computed spectra. The dyes selected for investigation here span a large range of molecular sizes and chemical functionalities and are embedded in solvents with different polarities. We have also investigated if the method is able to correctly reproduce the impact of a single chemical modification on the absorption energy. To characterize the method in more specific terms, we have studied four large BODIPY analogues used in real-life applications due to their interesting chemical properties. These examples should illustrate the capacity of the DLPNO-STEOM-CCSD procedure to become a method of choice for the study of photophysical properties of medium to large organic compounds.
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accurate band gap predictions of semiconductors in the framework of the similarity Transformed Equation of motion coupled cluster theory
Inorganic Chemistry, 2019Co-Authors: Anneke Dittmer, Frank Neese, Robert Izsak, Dimitrios MaganasAbstract:In this work, we present a detailed comparison between wave-function-based and particle/hole techniques for the prediction of band gap energies of semiconductors. We focus on the comparison of the back-Transformed Pair Natural Orbital Similarity Transformed Equation of Motion Coupled-Cluster (bt-PNO-STEOM-CCSD) method with Time Dependent Density Functional Theory (TD-DFT) and Delta Self Consistent Field/DFT (Δ-SCF/DFT) that are employed to calculate the band gap energies in a test set of organic and inorganic semiconductors. Throughout, we have used cluster models for the calculations that were calibrated by comparing the results of the cluster calculations to periodic DFT calculations with the same functional. These calibrations were run with cluster models of increasing size until the results agreed closely with the periodic calculation. It is demonstrated that bt-PNO-STEOM-CC yields accurate results that are in better than 0.2 eV agreement with the experiment. This holds for both organic and inorganic semiconductors. The efficiency of the employed computational protocols is thoroughly discussed. Overall, we believe that this study is an important contribution that can aid future developments and applications of excited state coupled cluster methods in the field of solid-state chemistry and heterogeneous catalysis.
Denis Bokhan - One of the best experts on this subject based on the ideXlab platform.
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similarity Transformed Equation of motion coupled cluster singles and doubles method with spin orbit effects for excited states
Journal of Chemical Physics, 2019Co-Authors: Denis Bokhan, D N Trubnikov, Ajith Perera, Rodney J BartlettAbstract:The similarity Transformed Equation-of-motion coupled-cluster method (STEOM-CCSD) for excited states is extended to treat spin-orbit coupling interactions (SOIs) using the spin-orbit mean field approximation of the Breit-Pauli Hamiltonian. Two possible schemes to include the spin-orbit splittings of excited states within the STEOM-CCSD model are formulated. They are identified as “diagonalize-then-perturb” and “perturb-then-diagonalize” approaches. The second approach is more suited for cases where SOI is larger, and the first approach breaks down. With the aid of the standard many-body diagrammatic techniques, expressions for all the necessary matrix elements can be derived. These new formulations are implemented in the ACES III suite of parallel coupled cluster programs, and benchmark studies are performed. Numerical tests for several atoms and molecules show a good agreement of calculated spin-orbit splittings to experiment, while also documenting the numerical differences between the two approaches.
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similarity Transformed Equation of motion coupled cluster singles and doubles method with spin orbit effects for excited states
Journal of Chemical Physics, 2019Co-Authors: Denis Bokhan, D N Trubnikov, Ajith Perera, Rodney J BartlettAbstract:The similarity Transformed Equation-of-motion coupled-cluster method (STEOM-CCSD) for excited states is extended to treat spin-orbit coupling interactions (SOIs) using the spin-orbit mean field approximation of the Breit-Pauli Hamiltonian. Two possible schemes to include the spin-orbit splittings of excited states within the STEOM-CCSD model are formulated. They are identified as “diagonalize-then-perturb” and “perturb-then-diagonalize” approaches. The second approach is more suited for cases where SOI is larger, and the first approach breaks down. With the aid of the standard many-body diagrammatic techniques, expressions for all the necessary matrix elements can be derived. These new formulations are implemented in the ACES III suite of parallel coupled cluster programs, and benchmark studies are performed. Numerical tests for several atoms and molecules show a good agreement of calculated spin-orbit splittings to experiment, while also documenting the numerical differences between the two approaches.The similarity Transformed Equation-of-motion coupled-cluster method (STEOM-CCSD) for excited states is extended to treat spin-orbit coupling interactions (SOIs) using the spin-orbit mean field approximation of the Breit-Pauli Hamiltonian. Two possible schemes to include the spin-orbit splittings of excited states within the STEOM-CCSD model are formulated. They are identified as “diagonalize-then-perturb” and “perturb-then-diagonalize” approaches. The second approach is more suited for cases where SOI is larger, and the first approach breaks down. With the aid of the standard many-body diagrammatic techniques, expressions for all the necessary matrix elements can be derived. These new formulations are implemented in the ACES III suite of parallel coupled cluster programs, and benchmark studies are performed. Numerical tests for several atoms and molecules show a good agreement of calculated spin-orbit splittings to experiment, while also documenting the numerical differences between the two approaches.
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explicitly correlated similarity Transformed Equation of motion coupled cluster method
Journal of Chemical Physics, 2015Co-Authors: Denis Bokhan, D N Trubnikov, Rodney J BartlettAbstract:Similarity Transformed Equation-of-motion method, based on linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] model, has been formulated and implemented. An extension of similarity transformation operator is introduced in order to treat short-range correlation effects for excited states. Additionally, effective reduction of the number of active virtuals can be obtained by such modification. Numerical tests for sets of valence and Rydberg excited states of several molecules are conducted. Statistical measures of errors in excitation energies show that explicitly correlated results are accurate up to 0.1 e.V already at a double-ζ level compared to those in the complete basis set limit, if the excitation energy is not too close to an ionization threshold. An example of long-range charge transfer excitation is also considered and highly accurate results are obtained.
