Search results for "Density Functional Theory"
showing 10 items of 981 documents
Ab Initio Calculations of the Transfer and Aggregation of F Centers in CaF2
2012
The F center and R center in CaF2 crystals have been studied by using density functional theory (DFT) with a hybrid B3PW description of exchange and correlation. Our calculations show that the F-center diffusion barrier is equal to 1.67 eV. During the F-center transfer, the trapped electron is more delocalized than that in the regular F-center case, and the gap between defect level and CB in the α-spin state decreases. The surface F-center investigation shows the trend of F centers to locate near the surface. The association energy calculations of R centers indicate stable aggregations of isolated F centers. During the F-center aggregation, a considerable covalency forms between two neighbo…
Ab initio calculations for the F-center transfer and R centers in SrF2
2013
We have simulated the F-center transfer and R center in SrF2 crystal by using density functional theory (DFT) with a hybrid B3PW description of exchange and correlation. Our calculations show that the F-center diffusion barrier is equal to 1.84 eV. During the F-center transfer, the trapped electron is more delocalized than that in the regular F-center case, and the gap between defect level and conduction bands (CB) in the a-spin state decreases. The formation energy calculations of R center show the trend of F centers to aggregate in SrF2. During the F-center aggregation, a considerable covalency forms between two neighboring fluorine vacancies with trapped electrons. Three incompletely pai…
Adiabatic versus Non-Adiabatic Electron Transfer at 2D Electrode Materials
2021
<div><div><div><p>Outer-sphere electron transfer (OS-ET) is a cornerstone elementary electrochemical reaction, yet microscopic understanding is largely based on idealized theories, developed in isolation from experiments that themselves are often close to the kinetic (diffusion) limit. Focusing on graphene as-grown on a copper substrate as a model 2D material/metal-supported electrode system, this study resolves the key electronic interactions in OS-ET, and identifies the role of graphene in modulating the electronic properties of the electrode/electrolyte interface. An integrated experimental-theoretical approach combining co-located multi-microscopy, centered on sc…
Quantitative prediction of gas-phase F19 nuclear magnetic shielding constants
2008
Benchmark calculations of (19)F nuclear magnetic shielding constants are presented for a set of 28 molecules. Near-quantitative accuracy (ca. 2 ppm deviation from experiment) is achieved if (1) electron correlation is adequately treated by employing the coupled-cluster singles and doubles (CCSD) model augmented by a perturbative correction for triple excitations [CCSD(T)], (2) large (uncontracted) basis sets are used, (3) gauge-including atomic orbitals are used to ensure gauge-origin independence, (4) calculations are performed at accurate equilibrium geometries [obtained from CCSD(T)/cc-pVTZ calculations correlating all electrons], and (5) vibrational averaging and temperature corrections…
First-principles calculations for SrTiO3() surface structure
2002
As a continuation of our recent abinitio calculations of SrTiO 3(1 0 0) surface relaxation for the two different terminations (SrO and TiO2) [Phys. Rev. B 64 (2001) 23417], we analyze here their electronic structures (band structure, density of states, and the electronic density redistribution with emphasis on the covalency effects). We compare results of abinitio Hartree–Fock method with electron correlation corrections and density functional theory with different exchange-correlation functionals, including hybrid (B3PW, B3LYP) exchange techniques. Our results are also compared with previous abinitio plane-wave local density approximation calculations and experiments when availab le. Consi…
Quantitative prediction of gas-phase N15 and P31 nuclear magnetic shielding constants
2010
High-level ab initio benchmark calculations of the (15)N and (31)P NMR chemical shielding constants for a representative set of molecules are presented. The computations have been carried out at the Hartree-Fock self-consistent field (HF-SCF), density functional theory (DFT) (B-P86 and B3-LYP), second-order Moller-Plesset perturbation theory (MP2), coupled cluster singles and doubles (CCSD), and CCSD augmented by a perturbative treatment of triple excitations [CCSD(T)] level of theory using basis sets of triple zeta quality or better. The influence of the geometry, the treatment of electron correlation, as well as basis set and zero-point vibrational effects on the shielding constants are d…
First Principles Calculations of Atomic and Electronic Structure of Ti3+Al- and Ti2+Al-Doped YAlO3
2021
M.G.B. appreciates support from the Chongqing Recruitment Program for 100 Overseas Innovative Talents (grant no. 2015013), the Program for the Foreign Experts (grant no. W2017011), Wenfeng High-end Talents Project (grant no. W2016-01) offered by the Chongqing University of Posts and Telecommunications (CQUPT), Estonian Research Council grant PUT PRG111, European Regional Development Fund (TK141), and NCN project 2018/31/B/ST4/00924. This study was supported by a grant from Latvian Research Council No. LZP-2018/1-0214 (for AIP). Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Program H202…
Heterovalent BiIII/PbII ionic substitution in one-dimensional trimethylsulfoxonium halide pseudo-perovskites (X = I, Br)
2021
We report on the synthesis and characterization of novel lead and bismuth hybrid (organic-inorganic) iodide and bromide pseudo-perovskites (ABX3) containing the trimethylsulfoxonium cation (CH3)3SO+ (TMSO) in the A site, Pb/Bi in the B site, and Br or I as X anions. All of these compounds are isomorphic and crystallize in the orthorhombic Pnma space group. Lead-based pseudo-perovskites consist of one-dimensional (1D) chains of face-sharing [PbX6] octahedra, while in the bismuth-based ones, the chains of [BiX6] are interrupted, with one vacancy every third site, leading to a zero-dimensional (0D) local structure based on separated [Bi2I9]3- dimers. Five solid solutions for the iodide with di…
Uncovering the metastable γ-Ag2WO4 phase: a joint experimental and theoretical study
2017
The synthesis of metastable solid phases is a pivotal starting point for innovative materials research. Here, we report the synthesis by means of a precipitation method of the metastable cubic γ-Ag2WO4 phase under ambient conditions. Different experimental techniques such as X-ray diffraction (XRD) with Rietveld refinement, field emission scanning electron microscopy (FE-SEM), micro-Raman/ultraviolet-visible (UV-vis) diffuse reflectance, photoluminescence spectroscopies, and differential scanning calorimetry (DSC) were employed. To complement the experimental data, the geometry, morphology, vibrational and electronic structure of γ-Ag2WO4 were characterized and evaluated using first-princip…
Graph-based analysis of ethylene glycol decomposition on a palladium cluster
2017
The ethylene glycol, CH2OH-CH2OH, decomposition mechanism, occurring on a subnanometric palladium cluster shaped by 12 atoms, was investigated by means of density functional theory. Different reaction routes were identified leading to H2 and CO. The whole reaction network was analyzed, framing the results within the graph theory. The possible decomposition pathways were discussed and compared, allowing one to draw a whole picture of all the parallel, possibly competitive, routes that starting from CH2OH-CH2OH originate H2 and CO.