Molecular Structure, Thermodynamic and Spectral Characteristics of Metal-Free and Nickel Complex of Tetrakis(1,2,5-thiadiazolo)porphyrazine

<div> <div> <div> <p>The study of photochemical reaction dynamics requires accurate as well as computationally efficient electronic structure methods for the ground and excited states. While time-dependent density functional theory (TDDFT) is not able to capture static correlation, complete active space self-consistent field (CASSCF) methods neglect much of the dynamic correlation. Hence, inexpensive methods that encompass both static and dynamic electron correlation effects are of high interest. Here, we revisit hole-hole Tamm-Dancoff approximated (<i>hh</i>-TDA) density functional theory for this purpose. The <i>hh</i>-TDA method is the hole-hole counterpart to the more established particle-particle TDA (<i>pp</i>-TDA) method, both of which are derived from the particle-particle random phase approximation (<i>pp</i>-RPA). In <i>hh</i>-TDA, the <i>N</i>-electron electronic states are obtained through double annihilations starting from a doubly anionic (<i>N</i>+2 electron) reference state. In this way, <i>hh</i>-TDA treats ground and excited states on equal footing, thus allowing for conical intersections to be correctly described. The treatment of dynamic correlation is introduced through the use of commonly-employed density functional approximations to the exchange-correlation potential. We show that hh-TDA is a promising candidate to efficiently treat the photochemistry of organic and biochemical systems that involve several low-lying excited states – particularly those with both low-lying pipi* and npi* states where inclusion of dynamic correlation is essential to describe the relative energetics. In contrast to the existing literature on <i>pp</i>-TDA and <i>pp</i>-RPA, we employ a functional-dependent choice for the response kernel in <i>pp</i>- and <i>hh</i>-TDA, which closely resembles the response kernels occurring in linear response and collinear spin-flip TDDFT.</p> </div> </div> </div>

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Straining to React: Delocalization Drives the Stability and Omniphilicity of [1.1.1]propellane

10.26434/chemrxiv.9733628.v1 ◽

2019 ◽

Author(s):

Alistair Sterling ◽

Russell C. Smith ◽

Edward Anderson ◽

Fernanda Duarte

Keyword(s):

Electronic Structure ◽

Electron Density ◽

Ground State ◽

State Of The Art ◽

Coupled Cluster ◽

Complete Active Space ◽

The Stability ◽

Highly Strained ◽

Cluster Methods ◽

Homo Lumo

The highly strained caged hydrocarbon [1.1.1]propellane has long fascinated chemists with its seemingly paradoxical stability, yet promiscuous reactivity. In this work, we present a unified model of reactivity that accounts for its omniphilic character. Through Complete Active Space (CAS) calculations, state-of-the-art coupled-cluster methods [DLPNO-CCSD(T)] and DFT approaches, we challenge the hypothesis that reactivity of [1.1.1]propellane is driven by strain relief. Instead, a highly delocalized ground-state electronic structure is proposed, where HOMO-LUMO mixing gives a moldable electron density that results in omniphilicity.

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Hole-Hole Tamm-Dancoff-Approximated Density Functional Theory: A Highly Efficient Electronic Structure Method Incorporating Dynamic and Static Correlation

10.26434/chemrxiv.11828256 ◽

2020 ◽

Author(s):

Christoph Bannwarth ◽

Jimmy K. Yu ◽

Edward G. Hohenstein ◽

Todd J. Martínez

Keyword(s):

Density Functional Theory ◽

Electronic Structure ◽

Excited States ◽

Density Functional ◽

Random Phase ◽

Computationally Efficient ◽

Functional Theory ◽

Complete Active Space ◽

Dynamic Correlation ◽

Static Correlation

<div> <div> <div> <p>The study of photochemical reaction dynamics requires accurate as well as computationally efficient electronic structure methods for the ground and excited states. While time-dependent density functional theory (TDDFT) is not able to capture static correlation, complete active space self-consistent field (CASSCF) methods neglect much of the dynamic correlation. Hence, inexpensive methods that encompass both static and dynamic electron correlation effects are of high interest. Here, we revisit hole-hole Tamm-Dancoff approximated (<i>hh</i>-TDA) density functional theory for this purpose. The <i>hh</i>-TDA method is the hole-hole counterpart to the more established particle-particle TDA (<i>pp</i>-TDA) method, both of which are derived from the particle-particle random phase approximation (<i>pp</i>-RPA). In <i>hh</i>-TDA, the <i>N</i>-electron electronic states are obtained through double annihilations starting from a doubly anionic (<i>N</i>+2 electron) reference state. In this way, <i>hh</i>-TDA treats ground and excited states on equal footing, thus allowing for conical intersections to be correctly described. The treatment of dynamic correlation is introduced through the use of commonly-employed density functional approximations to the exchange-correlation potential. We show that hh-TDA is a promising candidate to efficiently treat the photochemistry of organic and biochemical systems that involve several low-lying excited states – particularly those with both low-lying pipi* and npi* states where inclusion of dynamic correlation is essential to describe the relative energetics. In contrast to the existing literature on <i>pp</i>-TDA and <i>pp</i>-RPA, we employ a functional-dependent choice for the response kernel in <i>pp</i>- and <i>hh</i>-TDA, which closely resembles the response kernels occurring in linear response and collinear spin-flip TDDFT.</p> </div> </div> </div>

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Hole-Hole Tamm-Dancoff-Approximated Density Functional Theory: A Highly Efficient Electronic Structure Method Incorporating Dynamic and Static Correlation

10.26434/chemrxiv.11828256.v1 ◽

2020 ◽

Author(s):

Christoph Bannwarth ◽

Jimmy K. Yu ◽

Edward G. Hohenstein ◽

Todd J. Martínez

Keyword(s):

Density Functional Theory ◽

Electronic Structure ◽

Excited States ◽

Density Functional ◽

Random Phase ◽

Density Functional Theory Method ◽

Functional Theory ◽

Complete Active Space ◽

Dynamic Correlation ◽

Static Correlation

<div> <div> <div> <p>The study of photochemical reaction dynamics requires accurate as well as computationally efficient electronic structure methods for the ground and excited states. While time-dependent density functional theory (TDDFT) is not able to capture static correlation, complete active space self-consistent field (CASSCF) methods are deficient in their ability to describe dynamic correlation. Hence, inexpensive methods that encompass both static and dynamic electron correlation effects are of high interest. Here, we describe the hole-hole Tamm- Dancoff approximated (<i>hh</i>-TDA) density functional theory method, which is closely related to the previously established particle-particle random phase approximation (<i>pp</i>-RPA) and its TDA variant (<i>pp</i>-TDA). In <i>hh</i>-TDA, the <i>N</i>-electron electronic states are obtained through double annihilations starting from a doubly anionic (<i>N</i>+2 electron) reference state. In this way, <i>hh</i>-TDA treats ground and excited states on equal footing, thus allowing for conical intersections to be correctly described. The treatment of dynamic correlation is introduced through the use of commonly-employed density functional approximations to the exchange-correlation potential. <i>hh</i>-TDA appears to be a promising candidate to efficiently treat the photochemistry of organic and biochemical systems that involve several low-lying excited states – particularly those with both low-lying pipi* and npi* states where inclusion of dynamic correlation is essential to describe the relative energetics. In contrast to the existing literature on <i>pp</i>-TDA, we employ a functional- dependent choice for the response kernel in <i>pp</i>- and <i>hh</i>-TDA, which closely resembles the response kernels occurring in linear response and collinear spin-flip TDDFT. </p> </div> </div> </div>

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Study of thermal stability of n-type skutterudites Sr0.07Ba0.07Yb0.07Co4Sb12 by differential thermal analysis and Knudsen effusion method

Calphad ◽

10.1016/j.calphad.2021.102258 ◽

2021 ◽

Vol 73 ◽

pp. 102258

Author(s):

František Zelenka ◽

Jakub Strádal ◽

Pavel Brož ◽

Jan Vřešťál ◽

Jiří Buršík ◽

...

Keyword(s):

Thermal Stability ◽

Thermal Analysis ◽

Differential Thermal Analysis ◽

Knudsen Effusion ◽

Knudsen Effusion Method ◽

Effusion Method ◽

Thermal Stability Of

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Electronic Structure Study of Divanadium Complexes with Rigid Covalent Coordination: Potential Molecular Qubits with Slow Spin Relaxation

Dalton Transactions ◽

10.1039/d1dt00709b ◽

2021 ◽

Author(s):

Stephen Sproules

Keyword(s):

Electronic Structure ◽

Spin Relaxation ◽

Ground State ◽

Electronic Structures ◽

Structure Study ◽

Ligand Shell

The electronic structures of homovalent [V2(μ-S2)2(R2dtc)4] (R = Et, iBu) and mixed-valent [V2(μ-S2)2(R2dtc)4]+ are reported here. The soft-donor, eight-coordinate ligand shell combined with the fully delocalised ground state provides a...

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Magnetic Ground State and Electronic Structure Calculations of PbMnO3 Using DFT

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.895.420 ◽

2014 ◽

Vol 895 ◽

pp. 420-423 ◽

Cited By ~ 4

Author(s):

Sathya Sheela Subramanian ◽

Baskaran Natesan

Keyword(s):

Electronic Structure ◽

Band Structure ◽

Fermi Level ◽

Ground State ◽

Density Functional ◽

Electronic Structure Calculations ◽

Magnetic Ground State ◽

Electronic Band ◽

Structure Calculations ◽

Centrosymmetric Structure

Structural optimization, magnetic ground state and electronic structure calculations of tetragonal PbMnO3have been carried out using local density approximation (LDA) implementations of density functional theory (DFT). Structural optimizations were done on tetragonal P4mm (non-centrosymmetric) and P4/mmm (centrosymmetric) structures using experimental lattice parameters and our results indicate that P4mm is more stable than P4/mmm. In order to determine the stable magnetic ground state of PbMnO3, total energies for different magnetic configurations such as nonmagnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) were computed for both P4mm and P4/mmm structures. The total energy results reveal that the FM non-centrosymmetric structure is found to be the most stable magnetic ground state. The electronic band structure, density of states (DOS) and the electron localization function (ELF) were calculated for the stable FM structure. ELF revealed the distorted non-centrosymmetric structure. The band structure and DOS for the majority spins of FM PbMnO3showed no band gap at the Fermi level. However, a gap opens up at the Fermi level in minority spin channel suggesting that it could be a half-metal and a potential spintronic candidate.

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