scholarly journals Stabilizing hidden room-temperature ferroelectricity via a metastable atomic distortion pattern

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Jeong Rae Kim ◽  
Jinhyuk Jang ◽  
Kyoung-June Go ◽  
Se Young Park ◽  
Chang Jae Roh ◽  
...  
Keyword(s):  
Density Functional ◽  
Room Temperature ◽  
Deep Neural Network ◽  
Close Correlation ◽  
Perovskite Oxides ◽  
Atomic Scale ◽  
Neural Network Analysis ◽  
Functional Theory ◽  
Atomic Structures ◽  
Equilibrium Pattern

Abstract Nonequilibrium atomic structures can host exotic and technologically relevant properties in otherwise conventional materials. Oxygen octahedral rotation forms a fundamental atomic distortion in perovskite oxides, but only a few patterns are predominantly present at equilibrium. This has restricted the range of possible properties and functions of perovskite oxides, necessitating the utilization of nonequilibrium patterns of octahedral rotation. Here, we report that a designed metastable pattern of octahedral rotation leads to robust room-temperature ferroelectricity in CaTiO3, which is otherwise nonpolar down to 0 K. Guided by density-functional theory, we selectively stabilize the metastable pattern, distinct from the equilibrium pattern and cooperative with ferroelectricity, in heteroepitaxial films of CaTiO3. Atomic-scale imaging combined with deep neural network analysis confirms a close correlation between the metastable pattern and ferroelectricity. This work reveals a hidden but functional pattern of oxygen octahedral rotation and opens avenues for designing multifunctional materials.

Laser Irradiation of Atomic Chains: A Show-Case Study Based on the Density Functional Theory

2006 ◽  
Vol 960 ◽  
Author(s):  
Anna M. Mazzone ◽  
Marco Bianconi
Keyword(s):  
Density Functional Theory ◽  
Laser Irradiation ◽  
Density Functional ◽  
Laser Pulses ◽  
Chain Structure ◽  
Atomic Scale ◽  
Functional Theory ◽  
Atomic Structures ◽  
The Density Functional Theory ◽  
Atomic Chains

ABSTRACTThis study is motivated by recent applications of short laser pulses to the manipulation of atomic structures at the atomic scale and is based on the Density Functional Theory. The structures considered are linear monoatomic chains, formed by covalent and metallic atoms, and the calculations illustrate their evolution under laser irradiation. The calaculations show that the modification of the chain structure spans from a slight relaxation of the interatomic distances to fragmentation and illustrate the times and energies needed to induce those changes.

scholarly journals Metal-Rich Metallaboranes: Synthesis, Structures and Bonding of Bi- and Trimetallic Open-Faced Cobaltaboranes

Inorganics ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 28
Author(s):  
Kriti Pathak ◽  
Chandan Nandi ◽  
Jean-François Halet ◽  
Sundargopal Ghosh
Keyword(s):  
Electronic Structures ◽  
Density Functional ◽  
Room Temperature ◽  
Electron Pair ◽  
X Ray Diffraction ◽  
Functional Theory ◽  
X Ray ◽  
Cluster 2 ◽  
Cobalt Center

Synthesis, isolation, and structural characterization of unique metal rich diamagnetic cobaltaborane clusters are reported. They were obtained from reactions of monoborane as well as modified borohydride reagents with cobalt sources. For example, the reaction of [Cp*CoCl]2 with [LiBH4·THF] and subsequent photolysis with excess [BH3·THF] (THF = tetrahydrofuran) at room temperature afforded the 11-vertex tricobaltaborane nido-[(Cp*Co)3B8H10] (1, Cp* = η5-C5Me5). The reaction of Li[BH2S3] with the dicobaltaoctaborane(12) [(Cp*Co)2B6H10] yielded the 10-vertex nido-2,4-[(Cp*Co)2B8H12] cluster (2), extending the library of dicobaltadecaborane(14) analogues. Although cluster 1 adopts a classical 11-vertex-nido-geometry with one cobalt center and four boron atoms forming the open pentagonal face, it disobeys the Polyhedral Skeletal Electron Pair Theory (PSEPT). Compound 2 adopts a perfectly symmetrical 10-vertex-nido framework with a plane of symmetry bisecting the basal boron plane resulting in two {CoB3} units bridged at the base by two boron atoms and possesses the expected electron count. Both compounds were characterized in solution by multinuclear NMR and IR spectroscopies and by mass spectrometry. Single-crystal X-ray diffraction analyses confirmed the structures of the compounds. Additionally, density functional theory (DFT) calculations were performed in order to study and interpret the nature of bonding and electronic structures of these complexes.

scholarly journals Isolation of a Bimetallic Cobalt(III) Nitride and Examination of its Hydrogen Atom Abstraction Chemistry and Reactivity Towards H2

2020 ◽  
Author(s):  
Debabrata Sengupta ◽  
Christian Sandoval-Pauker ◽  
Emily Schueller ◽  
Angela M. Encerrado-Manriquez ◽  
Alejandro J. Metta-Magaña ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Density Functional ◽  
Room Temperature ◽  
Hydrogen Atom Abstraction ◽  
Functional Theory ◽  
Kinetic Rate ◽  
Rate Analysis ◽  
Stable Product ◽  
Activation Pathways ◽  
Computational Analyses

Room temperature photolysis of the bis(azide)cobaltate(II) complex [Na(THF)<sub>x</sub>][(<sup>ket</sup>guan)Co(N3)2] (<sup>ket</sup>guan = [(tBu2CN)C(NDipp)2]–, Dipp = 2,6-diisopropylphenyl) (3a) in THF cleanly forms the binuclear cobalt nitride [Na(THF)4{[(<sup>ket</sup>guan)Co(N3)]2(μ-N)}]<sub>n</sub> (1). Compound 1 represents the first example of an isolable, bimetallic cobalt nitride complex, and it has been fully characterized by spectroscopic, magnetic, and computational analyses. Density functional theory supports a CoIII=N=CoIII canonical form with significant π-bonding between the cobalt centers and the nitride atom. Unlike other Group 9 bridging nitride complexes, no radical character is detected at the bridging N-atom of 1. Indeed, 1 is unreactive towards weak C-H donors and even co-crystallizes with a molecule of cyclohexadiene (CHD) in its crystallographic unit cell to give 1·CHD as a room temperature stable product. Notably, addition of pyridine to 1 or photolyzed solutions of [(<sup>ket</sup>guan)Co(N3)(py)]<sub>2</sub> (4a) leads to destabilization via activation of the nitride unit, resulting in the mixed-valent Co(II)/(III) bridged imido species [(<sup>ket</sup>guan)Co]2(μ-NH)(μ-N3) (5) formed from intermolecular hydrogen atom abstraction (HAA) of strong C-H bonds (BDE ~ 100 kcal/mol). Kinetic rate analysis of the formation of 5 in the presence of C6H12 or C6D12 gives a KIE = 2.5±0.1, supportive of a HAA formation path-way. The reactivity of our system was further probed by photolyzing C6D6/py-d5 solutions of 4a under an H2 atmosphere (150 psi), which leads to the exclusive formation of the bis(imido)[(<sup>ket</sup>guan)Co(μ-NH)]2 (6) as a result of dihydrogen activa-tion. These results provide unique insights into the chemistry and electronic structure of late 3d-metal nitrides while providing entryway into C-H activation pathways.

scholarly journals DFT Studies of Graphene-Functionalised Derivatives of Capecitabine

2017 ◽  
Vol 72 (12) ◽  
pp. 1131-1138 ◽  
Author(s):  
Mehdi Aramideh ◽  
Mahmoud Mirzaei ◽  
Ghadamali Khodarahmi ◽  
Oğuz Gülseren
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Atomic Scale ◽  
Phase System ◽  
Molecular Models ◽  
Functional Theory ◽  
Atomic Properties ◽  
Scale Properties ◽  
Derivatives Of

AbstractCancer is one of the major problems for so many people around the world; therefore, dedicating efforts to explore efficient therapeutic methodologies is very important for researchers of life sciences. In this case, nanostructures are expected to be carriers of medicinal compounds for targeted drug design and delivery purposes. Within this work, the graphene (Gr)-functionalised derivatives of capecitabine (CAP), as a representative anticancer, have been studied based on density functional theory calculations. Two different sizes of Gr molecular models have been used for the functionalisation of CAP counterparts, CAP-Gr3 and CAP-Gr5, to explore the effects of Gr-functionalisation on the original properties of CAP. All singular and functionalised molecular models have been optimised and the molecular and atomic scale properties have been evaluated for the optimised structures. Higher formation favourability has been obtained for CAP-Gr5 in comparison with CAP-Gr3 and better structural stability has been obtained in the water-solvated system than the isolated gas-phase system for all models. The CAP-Gr5 model could play a better role of electron transferring in comparison with the CAP-Gr3 model. As a concluding remark, the molecular properties of CAP changed from singular to functionalised models whereas the atomic properties remained almost unchanged, which is expected for a carrier not to use significant perturbations to the original properties of the carried counterpart.

scholarly journals Atomic-Scale Understanding of Structure and Properties of Complex Pyrophosphate Crystals by First-Principles Calculations

2019 ◽  
Vol 9 (5) ◽  
pp. 840 ◽  
Author(s):  
Redouane Khaoulaf ◽  
Puja Adhikari ◽  
Mohamed Harcharras ◽  
Khalid Brouzi ◽  
Hamid Ez-Zahraouy ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Atomic Scale ◽  
Functional Theory ◽  
Local Structures ◽  
Cationic Group ◽  
Metallic Cations ◽  
Bonding And Bridging ◽  
Open Question

The electronic structure and mechanical and optical properties of five pyrophosphate crystals with very complex structures are studied by first principles density functional theory calculations. The results show the complex interplay of the minor differences in specific local structures and compositions can result in large differences in reactivity and interaction that are rare in other classes of inorganic crystals. These are discussed by dividing the pyrophosphate crystals into three structural units. H2P2O7 is the most important and dominating unit in pyrophosphates. The other two are the influential cationic group with metals and water molecules. The strongest P-O bond in P2O5 is the strongest bond for crystal cohesion, but O-H and N-H bonds also play an important part. Different type of bonding between O and H atoms such as O-H, hydrogen bonding, and bridging bonds are present. Metallic cations such as Mg, Zn, and Cu form octahedral bonding with O. The water molecule provides the unique H∙∙∙O bonds, and metallic elements can influence the structure and bonding to a certain extent. The two Cu-containing phosphates show the presence of narrow metallic bands near the valence band edge. All this complex bonding affects their physical properties, indicating that fundamental understanding remains an open question.

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