Density matrix renormalization group pair-density functional theory (DMRG-PDFT): singlet–triplet gaps in polyacenes and polyacetylenes

Sharma, Prachi; Bernales, Varinia; Knecht, Stefan; Truhlar, Donald G.; Gagliardi, Laura

doi:10.1039/c8sc03569e

Cited by 96 publications

(118 citation statements)

References 108 publications

(155 reference statements)

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“…Diradicals 2, 4 and 6 have central naphthalene unit contribution to the active space while for 8 and 10 this contribution is from central tetracene unit. This revelation is important here, as in literature the boundary of the originating open-shell ground state for oligoacene is roughly established at heptacene 18,73,74 and the delocalized radical also has the similar qualitative appearance 75,76. The exchange coupling constant values in this even-acene series decreases in going from 2 to 4 to 6 but increases in going from 6 to 8.…”

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confidence: 51%

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Kaur

Ali²

2020

Preprint

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The polyacene tend to transition from closed-shell to open-shell singlet systems with increase in the number of linearly fused benzene rings thus, enriching it's electronic as well as magnetic properties. Here, we have probed the role of such a polyacene couplers in mediating the magnetic exchange coupling between nitroxy radicals. For this, magnetic exchange coupling constants (2J) are computed employing broken-symmetry approach within density functional theory (DFT) as well as symmetry-adopted wave function based multi-configuration approach. Within DFT approach, apart from most commonly used exchange-correlation functional (generalized gradient approximation (GGA), meta-GGA, and hybrid) constrained spin density (CDFT) and on-site Coulomb correlation corrected GGA+U functionals have also been used to evaluate the exchange coupling constants in the diradicals. All DFT based methods approximate an exponential increase in the coupling constant values with increase in the length of the coupler. This is indeed an unexpected observation with no experimental report available to such an outcome by DFT calculations. Therefore, the electronic structures for these diradical systems with the increase in number of benzene rings were looked upon thoroughly. The properties like increase in number of degenerate or quasi-degenerate molecular orbitals (MOs), the lowering in energy of low-lying excited states and the development of intrinsic radical character of the coupler add to the complexity in evaluation of 2J values for such diradical systems with DFT approach. Consequently, wave function based multi-reference approach (CAASCF/NEVPT2) has been adopted. The active space has been limited to π-orbitals which are found to play an important role in the magnetic exchange interactions. With increase in the coupler size, the active space even with only π obitals would increase enormously which could not be taken into account even in the CASSCF study. The limited active space calculations also indicate quite strong exchange interaction, thus in principle, supporting the DFT observations of long-range magnetic exchange interactions but not an exponential increase in 2J with length of couplers.

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confidence: 51%

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Kaur

Ali²

2020

Preprint

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“…Recently it was used to evidence the different covalent and ionic contributions of the excited states of benzene [101] and to predict singlet-triplet gaps in large polyacenes and polyacetylenes in combination with DMRG. [102] As imilar method is the state-interaction state-average spin-restricted ensemblereferenced Kohn-Sham (SI-SA-REKS) method, [103] which combines dynamic correlation from DFT with am ulticonfigurational approach. This method is already sufficiently developed to have analytical gradients implemented [104] and has already been used in non-adiabatic dynamics simulations, for example,o fm olecular rotors [105] and biomimetic molecular switches.…”

Section: Hybrid Methods Combining Dft and Wave Function Theorymentioning

confidence: 99%

Molecular Photochemistry: Recent Developments in Theory

2020

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Photochemistry is a fascinating branch of chemistry that is concerned with molecules and light. However, the importance of simulating light‐induced processes is reflected also in fields as diverse as biology, material science, and medicine. This Minireview highlights recent progress achieved in theoretical chemistry to calculate electronically excited states of molecules and simulate their photoinduced dynamics, with the aim of reaching experimental accuracy. We focus on emergent methods and give selected examples that illustrate the progress in recent years towards predicting complex electronic structures with strong correlation, calculations on large molecules, describing multichromophoric systems, and simulating non‐adiabatic molecular dynamics over long time scales, for molecules in the gas phase or in complex biological environments.

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“…[101] Ebenso wurde es in Kombination mit DMRG fürd ie Vorhersage der Singulett-Triplett-Abstände großer Polyacene und Polyacetylene verwendet. [102] Eine weitere verwandte Methode ist der State-Interaction-State-Average-Spin-Restricted-Ensemble-Referenced-Kohn-Sham-Formalismus (SI-SA-REKS), [103] der eine Beschreibung der dynamischen Korrelationsenergie mittels DFT mit einem Multi-Konfigurations-Ansatz kombiniert. Diese Methode ist bereits soweit entwickelt, dass eine Implementierung analytischer Gradienten verfügbar ist.…”

Section: Multi-konfigurations-und Multi-referenz-methodenunclassified

Molekulare Photochemie: Moderne Entwicklungen in der theoretischen Chemie

Mai

González

2020

Angewandte Chemie

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Photochemie ist ein faszinierendes Teilgebiet der Chemie, das sich mit der Wechselwirkung von Molekülen und Licht befasst. Die Simulation von lichtinduzierten Prozessen spielt auch in anderen Forschungsgebieten wie Biologie, Materialwissenschaften oder Medizin eine bedeutende Rolle. Dieser Kurzaufsatz beleuchtet die jüngsten Entwicklungen in der theoretischen Chemie, die das Ziel haben, experimentelle Genauigkeit bei der Berechnung von elektronisch angeregten Zuständen von Molekülen und bei der Simulation von deren lichtinduzierten Dynamiken zu erreichen. Wir konzentrieren uns dabei auf neue, aufstrebende Methoden und zeigen ausgewählte Beispiele, welche die Fortschritte der letzten Jahre für folgende Themen aufzeigen: die Voraussage komplexer Elektronenstrukturen mit starker Korrelation, die Berechnung von großen Molekülen, die Beschreibung von multi‐chromophorischen Systemen und die Simulation nicht‐adiabatischer Moleküldynamik auf langen Zeitskalen; dies umfasst Moleküle sowohl in der Gasphase als auch in komplexer biologischer Umgebung.

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Density matrix renormalization group pair-density functional theory (DMRG-PDFT): singlet–triplet gaps in polyacenes and polyacetylenes

Abstract: The density matrix renormalization group (DMRG) is a powerful method to treat static correlation.

Cited by 96 publications

References 108 publications

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

First Principle Investigations of Long-range Magnetic Exchange Interactions via Polyacene Coupler

Molecular Photochemistry: Recent Developments in Theory

Molekulare Photochemie: Moderne Entwicklungen in der theoretischen Chemie

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