Local Enhancement of Dynamic Correlation in Excited States: Fresh Perspective on Ionicity and Development of Correlation Density Functional Approximation Based on the On-Top Pair Density

<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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Minimal-active-space multistate density functional theory for excitation energy involving local and charge transfer states

npj Computational Materials ◽

10.1038/s41524-021-00624-3 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Ruoqi Zhao ◽

Christian P. Hettich ◽

Xin Chen ◽

Jiali Gao

Keyword(s):

Density Functional Theory ◽

Charge Transfer ◽

Excited States ◽

Density Functional ◽

Good Description ◽

Dynamic Simulations ◽

Functional Theory ◽

Active Space ◽

Dynamic Correlation ◽

High Level

AbstractMultistate density functional theory (MSDFT) employing a minimum active space (MAS) is presented to determine charge transfer (CT) and local excited states of bimolecular complexes. MSDFT is a hybrid wave function theory (WFT) and density functional theory, in which dynamic correlation is first incorporated in individual determinant configurations using a Kohn–Sham exchange-correlation functional. Then, nonorthogonal configuration-state interaction is performed to treat static correlation. Because molecular orbitals are optimized separately for each determinant by including Kohn–Sham dynamic correlation, a minimal number of configurations in the active space, essential to representing low-lying excited and CT states of interest, is sufficient to yield the adiabatic states. We found that the present MAS-MSDFT method provides a good description of covalent and CT excited states in comparison with experiments and high-level computational results. Because of the simplicity and interpretive capability through diabatic configuration weights, the method may be useful in dynamic simulations of CT and nonadiabatic processes.

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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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Embracing local suppression and enhancement of dynamic correlation effects in a CASΠDFT method for efficient description of excited states

Faraday Discussions ◽

10.1039/d0fd00050g ◽

2020 ◽

Vol 224 ◽

pp. 333-347

Author(s):

Katarzyna Pernal ◽

Oleg V. Gritsenko

Keyword(s):

Excited States ◽

Correlation Energy ◽

Correlation Effects ◽

Dynamic Correlation

In this work we show that the presence of covalent and ionic configurations in a wavefunction gives rise to spatial regions where the effects of suppression and enhancement of correlation energy, respectively, dominate.

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Configurational entropy of a hard sphere system using modified density functional approximation (MWDA)

10.1063/1.5113066 ◽

2019 ◽

Author(s):

Arijit Mondal ◽

Leishangthem Premkumar ◽

Shankar P. Das

Keyword(s):

Hard Sphere ◽

Density Functional ◽

Configurational Entropy ◽

Functional Approximation

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Exploitation of Baird Aromaticity and Clar’s Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

Chemistry ◽

10.3390/chemistry3020038 ◽

2021 ◽

Vol 3 (2) ◽

pp. 532-549

Author(s):

Felix Plasser

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Excited States ◽

Aromatic Hydrocarbons ◽

Density Functional ◽

Materials Science ◽

Chemical Shifts ◽

Qualitative Description ◽

Triplet States ◽

Excitation Energies ◽

Polycyclic Aromatic

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four biphenylene-derived PAHs finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). The results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

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Study of Anharmonicity in Zirconium Hydrides Using Inelastic Neutron Scattering and Ab-Initio Computer Modeling

Inorganics ◽

10.3390/inorganics9050029 ◽

2021 ◽

Vol 9 (5) ◽

pp. 29

Author(s):

Jiayong Zhang ◽

Yongqiang Cheng ◽

Alexander I. Kolesnikov ◽

Jerry Bernholc ◽

Wenchang Lu ◽

...

Keyword(s):

Neutron Scattering ◽

Excited States ◽

Lattice Dynamics ◽

Density Functional ◽

Inelastic Neutron Scattering ◽

Inelastic Neutron ◽

Vibrational States ◽

Functional Theory ◽

Hydrogen Deuterium ◽

Zirconium Hydrides

The anharmonic phonon behavior in zirconium hydrides and deuterides, including ϵ-ZrH2, γ-ZrH, and γ-ZrD, has been investigated from aspects of inelastic neutron scattering (INS) and lattice dynamics calculations within the framework of density functional theory (DFT). The harmonic model failed to reproduce the spectral features observed in the experimental data, indicating the existence of anharmonicity in those materials and the necessity of further explanations. Here, we present a detailed study on the anharmonicity in zirconium hydrides/deuterides by exploring the 2D potential energy surface of hydrogen/deuterium atoms and solving the corresponding 2D single-particle Schrödinger equation to obtain the eigenfrequencies, which are then convoluted with the instrument resolution. The convoluted INS spectra qualitatively describe the anharmonic peaks in the experimental INS spectra and demonstrate that the anharmonicity originates from the deviations of hydrogen potentials from quadratic behavior in certain directions; the effects are apparent for the higher-order excited vibrational states, but small for the ground and first excited states.

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