MDPI - Publisher of Open Access Journals

13 pages, 1942 KB

Open AccessArticle

New Light on an Old Story: Breaking Kasha’s Rule in Phosphorescence Mechanism of Organic Boron Compounds and Molecule Design

by Dan Deng, Bingbing Suo and Wenli Zou

Int. J. Mol. Sci. 2022, 23(2), 876; https://doi.org/10.3390/ijms23020876 - 14 Jan 2022

Cited by 2 | Viewed by 2820

Abstract

In this work, the phosphorescence mechanism of (E)-3-(((4-nitrophenyl)imino)methyl)-2H-thiochroman-4-olate-BF2 compound (S-BF2) is investigated theoretically. The phosphorescence of S-BF2 has been reassigned to the second triplet state (

T_{2}

) by the density matrix renormalization group (DMRG) method combined with the multi-configurational pair density [...] Read more.

T_{2}

) by the density matrix renormalization group (DMRG) method combined with the multi-configurational pair density functional theory (MCPDFT) to approach the limit of theoretical accuracy. The calculated radiative and non-radiative rate constants support the breakdown of Kasha’s rule further. Our conclusion contradicts previous reports that phosphorescence comes from the first triplet state (

T_{1}

). Based on the revised phosphorescence mechanism, we have purposefully designed some novel compounds in theory to enhance the phosphorescence efficiency from

T_{2}

by replacing substitute groups in S-BF2. Overall, both S-BF2 and newly designed high-efficiency molecules exhibit anti-Kasha

T_{2}

phosphorescence instead of the conventional

T_{1}

emission. This work provides a useful guidance for future design of high-efficiency green-emitting phosphors. Full article

(This article belongs to the Special Issue Molecular Structure, Electronic and Vibrational Spectra Theoretical Calculations in Materials Sciences)

► Show Figures

Graphical abstract

11 pages, 744 KB

Open AccessArticle

Absence of Superconductivity in the Hubbard Dimer Model for κ-(BEDT-TTF)₂X

by Dipayan Roy, R. Torsten Clay and Sumit Mazumdar

Crystals 2021, 11(6), 580; https://doi.org/10.3390/cryst11060580 - 22 May 2021

Cited by 1 | Viewed by 2910

Abstract

In the most studied family of organic superconductors

κ

-(BEDT-TTF)

_{2}

X, the BEDT-TTF molecules that make up the conducting planes are coupled as dimers. For some anions X, an antiferromagnetic insulator is found at low temperatures adjacent to superconductivity. With an average [...] Read more.

In the most studied family of organic superconductors

κ

-(BEDT-TTF)

_{2}

\frac{1}{2}

-filled. Numerous theories have suggested that fluctuations of the magnetic order can drive superconducting pairing in these models, even as direct calculations of superconducting pairing in monomer

\frac{1}{2}

-filled band models find no superconductivity. Here, we present accurate zero-temperature Density Matrix Renormalization Group (DMRG) calculations of a dimerized lattice with one hole per dimer. While we do find an antiferromagnetic state in our results, we find no evidence for superconducting pairing. This further demonstrates that magnetic fluctuations in the effective

\frac{1}{2}

-filled band approach do not drive superconductivity in these and related materials. Full article

(This article belongs to the Special Issue Organic Conductors)

► Show Figures

Graphical abstract

17 pages, 1383 KB

Open AccessArticle

Many-Body Effects in FeN₄ Center Embedded in Graphene

by Andrew Allerdt, Hasnain Hafiz, Bernardo Barbiellini, Arun Bansil and Adrian E. Feiguin

Appl. Sci. 2020, 10(7), 2542; https://doi.org/10.3390/app10072542 - 7 Apr 2020

Cited by 14 | Viewed by 4786

Abstract

We introduce a computational approach to study porphyrin-like transition metal complexes, bridging density functional theory and exact many-body techniques, such as the density matrix renormalization group (DMRG). We first derive a multi-orbital Anderson impurity Hamiltonian starting from first principles considerations that qualitatively reproduce [...] Read more.

U^{'}

and Hund exchange J. An exact canonical transformation is used to reduce the dimensionality of the problem and make it amenable to DMRG calculations, including all many-body terms (both intra- and inter-orbital), which are treated in a numerically exact way. We apply this technique to FeN

_{4}

centers in graphene and show that the inclusion of these terms has dramatic effects: as the iron orbitals become single occupied due to the Coulomb repulsion, the inter-orbital interaction further reduces the occupation, yielding a non-monotonic behavior of the magnetic moment as a function of the interactions, with maximum polarization only in a small window at intermediate values of the parameters. Furthermore,

U^{'}

changes the relative position of the peaks in the density of states, particularly on the iron

d_{z^{2}}

orbital, which is expected to affect the binding of ligands greatly. Full article

(This article belongs to the Special Issue Modeling Transition-Metal Systems: Emerging Developments and Applications)

► Show Figures

Figure 1

17 pages, 3865 KB

Open AccessArticle

Disassembly of Faceted Macrosteps in the Step Droplet Zone in Non-Equilibrium Steady State

by Noriko Akutsu

Crystals 2017, 7(2), 42; https://doi.org/10.3390/cryst7020042 - 8 Feb 2017

Cited by 13 | Viewed by 6056

Abstract

A Wulff figure—the polar graph of the surface tension of a crystal—with a discontinuity was calculated by applying the density matrix renormalization group method to the p-RSOS model, a restricted solid-on-solid model with a point-contact-type step–step attraction. In the step droplet zone in this model, the surface tension is discontinuous around the (111) surface and continuous around the (001) surface. The vicinal surface of 4H-SiC crystal in a Si–Cr–C solution is thought to be in the step droplet zone. The dependence of the vicinal surface growth rate and the macrostep size

〈 n 〉

on the driving force

Δ μ

for a typical state in the step droplet zone in non-equilibrium steady state was calculated using the Monte Carlo method. In contrast to the known step bunching phenomenon, the size of the macrostep was found to decrease with increasing driving force. The detachment of elementary steps from a macrostep was investigated, and it was found that

〈 n 〉

satisfies a scaling function. Moreover, kinetic roughening was observed for

| Δ μ | > Δ μ_{R}

, where

Δ μ_{R}

is the crossover driving force above which the macrostep disappears. Full article

(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)

► Show Figures

Figure 1

Search Results (4)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (4)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI