Search results for "Density Functional Theory."

Large thermoelectric figure of merit in hexagonal phase of 2D selenium and tellurium

2020

An inconvenient influence of iridium(III) isomer on OLED efficiency.

2010

The recently reported heteroleptic cyclometallated iridium(III) complex [Ir(2-phenylpyridine)(2)(2-carboxy-4-dimethylaminopyridine)] N984 and its isomer N984b have been studied more in detail. While photo- and electrochemical properties are very similar, DFT/TDDFT calculations show that the two isomers have different HOMO orbital characteristics. As a consequence, solution processed OLEDs made using a mixture of N984 and isomer N984b similar to vacuum processed devices show that the isomer has a dramatic detrimental effect on the performances of the device. In addition, commonly used thermogravimetric analysis is not suitable for showing the isomerization process. The isomer could impact pe…

Oxadiazolyl-pyridines and perfluoroalkyl-carboxylic acids as building blocks for protic ionic liquids: crossing the thin line between ionic and hydro…

2012

A series of 18 samples has been prepared in order to obtain fluorinated materials as Protic Ionic Liquids (PILs). These were synthesized by appropriately mixing 1,2,4-oxadiazoles derivatised with two pyridines, or one pyridine and a fluorinated chain, and perfluoroalkyl-carboxylic acids, either mono- or dicarboxylic, leading to symmetric and non-symmetric materials. Many of them showed low melting points. However, the possibility of classifying the synthesized materials as PILs is discussed in terms of effective ionicity of the systems by the combination of Density Functional Theory (DFT) calculation and IR spectroscopy. The important outcome of our investigation is that the complete proton…

First-principles modelling for time-resolved ARPES under different pump-probe conditions

2021

First-principles methods for time-resolved angular resolved photoelectron spectroscopy play a pivotal role in providing interpretation and microscopic understanding of the complex experimental data and in exploring novel observables or observation conditions that may be achieved in future experiments. Here we describe an efficient, reliable and scalable first-principles method for tr-ARPES based on time-dependent density functional theory including propagation and surface effects usually discarded in the widely used many-body techniques based on computing the non-equilibrium spectral function and discuss its application to a variety of pump–probe conditions. We identify four conditions, dep…

Simulating pump-probe photo-electron and absorption spectroscopy on the attosecond time-scale with time-dependent density-functional theory

2013

Molecular absorption and photoelectron spectra can be efficiently predicted with real-time time-dependent density functional theory. We show herein how these techniques can be easily extended to study time-resolved pump-probe experiments, in which a system response (absorption or electron emission) to a probe pulse is measured in an excited state. This simulation tool helps with the interpretation of fast-evolving attosecond time-resolved spectroscopic experiments, in which electronic motion must be followed at its natural timescale. We show how the extra degrees of freedom (pump-pulse duration, intensity, frequency, and time delay), which are absent in a conventional steady-state experimen…

Compressibility and phase stability of iron-rich ankerite

2021

ABSTRACT: The structure of the naturally occurring, iron-rich mineral Ca₁․₀₈(₆)Mg₀.₂₄(₂)Fe₀.₆₄(₄)Mn₀.₆₄(₄)(CO₃)₂ ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch-Murnaghan equation of state yields V₀ = 328.2(3) ų, bulk modulus B₀ = 89(4) GPa, and its first-pressure derivative B'₀ = 5.3(8)-values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO₃)₂ ankerite composition. At 12 GPa, the iron-rich ankerite structure …

Synthesis, Characterization, and Properties of Weakly Coordinating Anions Based on tris-Perfluoro-tert-Butoxyborane

2017

A convenient method for the preparation of strongly Lewis acidic tris-perfluoro-tert-butoxyborane B(ORF)3 (1), (ORF = OC(CF3)3) was developed, and its X-ray structure was determined. 1 was used as a precursor, guided by density functional theory (DFT) calculations and volume-based thermodynamics, for the synthesis of [NEt4][NCB(ORF)3] (3) and [NMe4][FB(ORF)3] (5) and the novel large and weakly coordinating anion salts [Li 15-Crown-5][B(ORF)4] (2) and [NEt4][CN{B(ORF)3}2] (4). The stability of [B(ORF)4]− was compared with that of some related known weakly coordinating anions by appropriate DFT calculations.

Stark ionization of atoms and molecules within density functional resonance theory

2013

We show that the energetics and lifetimes of resonances of finite systems under an external electric field can be captured by Kohn–Sham density functional theory (DFT) within the formalism of uniform complex scaling. Properties of resonances are calculated self-consistently in terms of complex densities, potentials, and wave functions using adapted versions of the known algorithms from DFT. We illustrate this new formalism by calculating ionization rates using the complex-scaled local density approximation and exact exchange. We consider a variety of atoms (H, He, Li, and Be) as well as the H2 molecule. Extensions are briefly discussed.

Reactivity of the Superheavy Element 115, Mc, and Its Lighter Homologue, Bi, with Respect to Gold and Hydroxylated Quartz Surfaces from Periodic Rela…

2021

Adsorption energies (Eads) of the superheavy element (SHE) Mc, its lighter homologue (Bi), as well as of another superheavy element Nh and some lighter homologues of SHEs on gold and hydroxylated quartz surfaces are predicted via periodic relativistic density functional theory calculations. The aim of this study is to support "one-atom-at-a-time" gas-phase chromatography experiments that are examining the reactivity and volatility of Mc. The obtained Eads values of the Bi and Mc atoms on the Au(111) surface are >200 kJ/mol. On the hydroxylated quartz surface, Mc should adsorb with a minimal energy of 58 kJ/mol. On both types of surfaces, Eads(Mc) should be ∼100 kJ/mol smaller than Eads(Bi) …

Six-coordinate [CoIII(L)2]z (z = 1−, 0, 1+) complexes of an azo-appended o-aminophenolate in amidate(2−) and iminosemiquinonate π-radical (1−) redox-…

2018

Aerobic reaction of the ligand H2L1, 2-(2-phenylazo)-anilino-4,6-di-tert-butylphenol, CoCl2·6H2O and Et3N in MeOH under refluxing conditions produces, after work-up and recrystallization, black crystals of [Co(L1)2] (1). When examined by cyclic voltammetry, 1 displays in CH2Cl2 three one-electron redox responses: two oxidative, E11/2 = 0.30 V (peak-to-peak separation, ΔEp = 100 mV) and E21/2 = 1.04 V (ΔEp = 120 mV), and one reductive E1/2 = −0.27 V (ΔEp = 120 mV) vs. SCE. Consequently, 1 is chemically oxidized by 1 equiv. of [FeIII(η5-C5H5)2][PF6], affording the isolation of deep purple crystals of [Co(L1)2][PF6]·2CH2Cl2 (2), and one-electron reduction with [CoII(η5-C5H5)2] yielded bluish-b…