scholarly journals Multireference Ground and Excited State Electronic Structures of Free- versus Iron Porphyrin-Carbenes

2019 ◽  
Author(s):  
Gautam Stroscio ◽  
Martin Srnec ◽  
Ryan Hadt
Keyword(s):  
Excited State ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Closed Shell ◽  
Axial Ligand ◽  
Iron Porphyrin ◽  
Functional Theory ◽  
Reaction Coordinates ◽  
Ligand Charge Transfer ◽  
Energy Surfaces

Iron porphyrin carbenes (IPCs) are important reaction intermediates in engineered carbene transferase enzymes and homogeneous catalysis. However, discrepancies between theory and experiment complicate the understanding of IPC electronic structure (i.e., open- vs. closed-shell singlet (OSS vs. CSS)). Here we investigate the structurally dependent ground and excited spin state energetics of a free carbene and its IPC analogs. Only multireference <i>ab initio</i> wave function methods are consistent with experiment and predict a CSS ground state (Fe(II)←{:C(X)Y}<sup>0</sup>), contrary to density functional theory (DFT). The OSS is a high-lying metal-to-ligand charge transfer (MLCT) excited state that is sensitive to the nature of the axial ligand. Furthermore, potential energy surfaces (PESs) along the Fe–C bond elongation coordinate exhibit strong mixings between CSS/OSS characters, which can be an important feature for describing reaction mechanisms. Future studies on IPC reaction coordinates should evaluate contributions from ground and excited state multireference character. <br>

scholarly journals Multireference Ground and Excited State Electronic Structures of Free- versus Iron Porphyrin-Carbenes

2019 ◽  
Author(s):  
Gautam Stroscio ◽  
Martin Srnec ◽  
Ryan Hadt
Keyword(s):  
Excited State ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Closed Shell ◽  
Axial Ligand ◽  
Iron Porphyrin ◽  
Functional Theory ◽  
Reaction Coordinates ◽  
Ligand Charge Transfer ◽  
Energy Surfaces

Iron porphyrin carbenes (IPCs) are important reaction intermediates in engineered carbene transferase enzymes and homogeneous catalysis. However, discrepancies between theory and experiment complicate the understanding of IPC electronic structure (i.e., open- vs. closed-shell singlet (OSS vs. CSS)). Here we investigate the structurally dependent ground and excited spin state energetics of a free carbene and its IPC analogs. Only multireference <i>ab initio</i> wave function methods are consistent with experiment and predict a CSS ground state (Fe(II)←{:C(X)Y}<sup>0</sup>), contrary to density functional theory (DFT). The OSS is a high-lying metal-to-ligand charge transfer (MLCT) excited state that is sensitive to the nature of the axial ligand. Furthermore, potential energy surfaces (PESs) along the Fe–C bond elongation coordinate exhibit strong mixings between CSS/OSS characters, which can be an important feature for describing reaction mechanisms. Future studies on IPC reaction coordinates should evaluate contributions from ground and excited state multireference character. <br>

scholarly journals Multireference Ground and Excited State Electronic Structures of Free-Versus Iron Porphyrin-Carbenes

2019 ◽  
Author(s):  
Gautam Stroscio ◽  
Martin Srnec ◽  
Ryan Hadt
Keyword(s):  
Excited State ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Closed Shell ◽  
Axial Ligand ◽  
Iron Porphyrin ◽  
Functional Theory ◽  
Reaction Coordinates ◽  
Ligand Charge Transfer ◽  
Energy Surfaces

Iron porphyrin carbenes (IPCs) are important reaction intermediates in engineered carbene transferase enzymes and homogeneous catalysis. However, discrepancies between theory and experiment complicate the understanding of IPC electronic structure (i.e., open- vs. closed-shell singlet (OSS vs. CSS)). Here we investigate the structurally dependent ground and excited spin state energetics of a free carbene and its IPC analogs. Only multireference <i>ab initio</i> wave function methods are consistent with experiment and predict a CSS ground state (Fe(II)←{:C(X)Y}<sup>0</sup>), contrary to density functional theory (DFT). The OSS is a high-lying metal-to-ligand charge transfer (MLCT) excited state that is sensitive to the nature of the axial ligand. Furthermore, potential energy surfaces (PESs) along the Fe–C bond elongation coordinate exhibit strong mixings between CSS/OSS characters, which can be an important feature for describing reaction mechanisms. Future studies on IPC reaction coordinates should evaluate contributions from ground and excited state multireference character. <br>

scholarly journals The Photochemistry of Fe2(S2C3H6)(CO)6(µ-CO) and Its Oxidized Form, Two Simple [FeFe]-Hydrogenase CO-Inhibited Models. A DFT and TDDFT Investigation

Inorganics ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 16
Author(s):  
Federica Arrigoni ◽  
Giuseppe Zampella ◽  
Luca De Gioia ◽  
Claudio Greco ◽  
Luca Bertini
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Temperature Dependent ◽  
Cationic Form ◽  
Functional Theory ◽  
Co Dissociation ◽  
State Potential ◽  
Energy Surfaces

FeIFeI Fe2(S2C3H6)(CO)6(µ-CO) (1a–CO) and its FeIFeII cationic species (2a+–CO) are the simplest model of the CO-inhibited [FeFe] hydrogenase active site, which is known to undergo CO photolysis within a temperature-dependent process whose products and mechanism are still a matter of debate. Using density functional theory (DFT) and time-dependent density functional theory (TDDFT) computations, the ground state and low-lying excited-state potential energy surfaces (PESs) of 1a–CO and 2a+–CO have been explored aimed at elucidating the dynamics of the CO photolysis yielding Fe2(S2C3H6)(CO)6 (1a) and [Fe2(S2C3H6)(CO)6]+ (2a+), two simple models of the catalytic site of the enzyme. Two main results came out from these investigations. First, a–CO and 2a+–CO are both bound with respect to any CO dissociation with the lowest free energy barriers around 10 kcal mol−1, suggesting that at least 2a+–CO may be synthesized. Second, focusing on the cationic form, we found at least two clear excited-state channels along the PESs of 2a+–CO that are unbound with respect to equatorial CO dissociation.

scholarly journals The Photochemistry of Fe2(S2C3H6)(CO)6(µ-CO) and its Oxidized Form, Two Simple [FeFe]-Hydrogenase CO-Inhibited Models. A DFT and TDDFT Investigation

2021 ◽  
Author(s):  
Federica Arrigoni ◽  
Giuseppe Zampella ◽  
Luca De Gioia ◽  
Claudio Greco ◽  
Luca Bertini
Keyword(s):  
Density Functional Theory ◽  
Excited State ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Temperature Dependent ◽  
Cationic Form ◽  
Functional Theory ◽  
Co Dissociation ◽  
State Potential ◽  
Energy Surfaces

FeIFeI Fe2(S2C3H6)(CO)6(&micro;-CO) (1a-CO) and its FeIFeII cationic species (2a+-CO) are the simplest model of the CO-inhibited [FeFe] hydrogenase active site, which is known to undergo CO photolysis within a temperature- dependent process whose products and mechanism are still a matter of debate. Using Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TDDFT) computations, the ground state and low-lying excited state potential energy surfaces (PESs) of 1a-CO and 2a+-CO have been explored aimed at elucidating the dynamics of the CO photolysis yielding Fe2(S2C3H6)(CO)6 (1a) and Fe2(S2C3H6)(CO)6+ (2a+), two simple models of the catalytic site of the enzyme. Two main results came out from these investigations. First, a-CO and 2a+-CO are both bound with respect to any CO dissociation with lowest free energy barriers around 10 kcal mol-1, suggesting that at least 2a+-CO might be synthetized. Second, focusing on the cationic form, we found at least two clear excited state channels along the PESs of 2a+-CO that are unbound with respect to equatorial CO dissociation.

scholarly journals The ANI-1ccx and ANI-1x Data Sets, Coupled-Cluster and Density Functional Theory Properties for Molecules

2020 ◽  
Author(s):  
Justin S. Smith ◽  
Roman Zubatyuk ◽  
Benjamin T. Nebgen ◽  
Nicholas Lubbers ◽  
Kipton Barros ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Potential Energy Surfaces ◽  
Density Functional ◽  
Atomic Charge ◽  
Density Functional Theory Calculations ◽  
Coupled Cluster ◽  
Data Sets ◽  
Data Set ◽  
Functional Theory ◽  
Energy Surfaces

<p>Maximum diversification of data is a central theme in building generalized and accurate machine learning (ML) models. In chemistry, ML has been used to develop models for predicting molecular properties, for example quantum mechanics (QM) calculated potential energy surfaces and atomic charge models. The ANI-1x and ANI-1ccx ML-based eneral-purpose potentials for organic molecules were developed through active learning; an automated data diversification process. Here, we describe the ANI-1x and ANI-1ccx data sets. To demonstrate data set diversity, we visualize them with a dimensionality reduction scheme, and contrast against existing data sets. The ANI-1x data set contains multiple QM properties from 5M density functional theory calculations, while the ANI-1ccx data set contains 500k data points obtained with an accurate CCSD(T)/CBS extrapolation. Approximately 14 million CPU core-hours were expended to generate this data. Multiple QM properties from density functional theory and coupled cluster are provided: energies, atomic forces, multipole moments, atomic charges, and more. We provide this data to the community to aid research and development of ML models for chemistry.</p>

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