Search results for " function"
showing 10 items of 9395 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…
Nature of the ring-closure process along the rearrangement of octa-1,3,5,7-tetraene to cycloocta-1,3,5-triene from the perspective of the electron lo…
2011
We analyze the behavior of the energy profile of the ring-closure process for the transformation of (3Z,5Z)-octa-1,3,5,7-tetraene 5 to (1Z,3Z,5Z)-cycloocta-1,3,5-triene 6 through a combination of electron localization function (ELF) and catastrophe theory (CT). From this analysis, concepts such as bond breaking/forming processes, formation/annihilation of lone pairs, and other electron pair rearrangements arise naturally through the reaction progress simply in terms of the different ways of pairing up the electrons. A relationship between the topology and the nature of the bond breaking/forming processes along this rearrangement is reported. The different domains of structural stability of …
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…
Towards saturation of the electron-capture delayed fission probability: The new isotopes $^{240}Es$ and $^{236}Bk$
2016
Abstract The new neutron-deficient nuclei 240 Es and 236 Bk were synthesised at the gas-filled recoil separator RITU. They were identified by their radioactive decay chains starting from 240 Es produced in the fusion–evaporation reaction 209 Bi( 34 S,3n) 240 Es. Half-lives of 6 ( 2 ) s and 22 − 6 + 13 s were obtained for 240 Es and 236 Bk, respectively. Two groups of α particles with energies E α = 8.19 ( 3 ) MeV and 8.09 ( 3 ) MeV were unambiguously assigned to 240 Es. Electron-capture delayed fission branches with probabilities of 0.16 ( 6 ) and 0.04 ( 2 ) were measured for 240 Es and 236 Bk, respectively. These new data show a continuation of the exponential increase of ECDF probabilitie…
An ab initio study of the electron affinity of O2
1993
Abstract Coupled pair functional, multiconfigurational second-order perturbation theory, and multireference CI methods have been applied in a calculation of the electron affinity of the oxygen molecule. The convergence of the theoretical result has been checked with respect to a systematic expansion of the one-electron basis and the multireference CI wavefunction. The best calculated value, 0.39 eV, is 0.06 eV smaller than the recent experimental value 0.45±0.01 eV.
Ab Initio Methods for Excited States
2005
This chapter focuses mainly on the performance of ab initio methods for the description of spectroscopic molecular properties of compounds. Most of the quantum-chemical methods developed up to date are based on the concept of the one-electron wave function. The electronic states of a system with N electrons are described by a double expansion. Molecular orbitals (MOs) are one-electron wave functions expressed as linear combinations of a known one-electron basis set (K) and the N electron wave function is formulated in a many-electron basis set formed by determinants (or linear combination of them to form spin-adapted wave functions), built as normalized antisymmetric products of MOs. Accord…
Electron correlation effects on the calculated 13C NMR spectra of vinyl cations
1997
Abstract A study of calculated 13C NMR chemical shifts in vinyl cations is presented. The sensitivity of predicted isotropic shifts to correlation, basis set and geometry effects is explored. In order to obtain accurate estimates that are reasonably well converged with respect to further improvements in theory, it appears that the CCSD(T) method must be used with a basis of triple-zeta plus polarization quality on the carbon atoms. Second-order many-body perturbation theory performs adequately for all carbons except for that bearing the formal positive charge, while the self-consistent field approximation cannot be relied upon to predict even the correct qualitative ordering in the spectrum…
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…