Influence of the variation in the Hubbard parameter (U) on activation energies of CeO2-catalysed reactions

2020 ◽  
Vol 98 (4) ◽  
pp. 385-389 ◽  
Author(s):  
Hussein A. Miran ◽  
Mohammednoor Altarawneh ◽  
Zainab N. Jaf ◽  
M. Mahbubur Rahman ◽  
Mansour H. Almatarneh ◽  
...  
Keyword(s):  
Density Functional ◽  
Strongly Correlated ◽  
Kinetics Parameters ◽  
Kinetics Modelling ◽  
The Density Functional Theory ◽  
Daunting Task ◽  
Structural And Electronic Properties ◽  
U Value ◽  
Hubbard Parameter ◽  
Reaction Energies

Accurate description of thermodynamic, structural, and electronic properties for bulk and surfaces of ceria (CeO2) necessitates the inclusion of the Hubbard parameter (U) in the density functional theory (DFT) calculations to precisely account for the strongly correlated 4f electrons. Such treatment is a daunting task when attempting to draw a potential energy surface for CeO2-catalyzed reaction. This is due to the inconsistent change in thermo-kinetics parameters of the reaction in reference to the variation in the U values. As an illustrative example, we investigate herein the discrepancy in activation and reaction energies for steps underlying the partial and full hydrogenation of acetylene over the CeO2(111) surface. Overall, we find that both activation and reaction energies positively correlate with the increase in the U value. In addition to benchmarking against more accurate theoretical methodologies, we suggest that U values are better optimized against kinetics modelling of experimentally observed profiles of products from the catalytic-assisted system of reactions.

CH2O Adsorption on M (M = Li, Mg and Al) Atom Deposited ZnO Nano-Cage: DFT Study

2018 ◽  
Vol 786 ◽  
pp. 384-392 ◽  
Author(s):  
Hussein Y. Ammar
Keyword(s):  
Density Functional Theory ◽  
Bond Length ◽  
Density Functional ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties ◽  
Formaldehyde Molecule ◽  
Electronic Configurations ◽  
Adsorption Energies ◽  
Homo Lumo

The structural and electronic properties of Li, Mg and Al deposited ZnO nanocages and their effects on the adsorption of formaldehyde molecule have been investigated using the density functional theory (DFT) computations. To understand the behavior of the adsorbed CH2O molecule on the ZnO nanocage, results of DFT calculations of the M-deposited nanocages (M=Li, Mg and Al), as well as complex systems consisting of the adsorbed CH2O molecule on M-deposited ZnO nanocage were reported. The results presented include adsorption energies, bond lengths, electronic configurations, density of states and molecular orbitals. It was found that, the most energetically stable adsorption configurations of CH2O molecule on the bare ZnO leads to 12% dilation in C=O bond length of CH2O and 14% decrease in HOMO-LUMO gap of ZnO cluster. The most energetically stable adsorption configurations of CH2O molecule on Li, Mg and Al-deposited ZnO lead to 4%, 4% and 11% dilation in C=O bond length of CH2O and-0.66, -45 and , +66% change in HOMO-LUMO gap of ZnO nanocages, respectively. The interaction between CH2O with bare ZnO and M-deposited ZnO nanocages is attributed to charge transfer mechanism. These results may be meaningful for CH2O degradation and detection.

The Interaction between Graphene and the SiC Substrate: Ab Initio Calculations for Polar and Nonpolar Surfaces

2016 ◽  
Vol 858 ◽  
pp. 1125-1128
Author(s):  
Ioannis Deretzis ◽  
Filippo Giannazzo ◽  
Antonino La Magna
Keyword(s):  
Density Functional Theory ◽  
Energy Spectrum ◽  
Density Functional ◽  
Low Energy ◽  
Electrical Characteristics ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties ◽  
Exclusive Property

Notwithstanding the graphitization of SiC under high thermal treatment can take place for all SiC surfaces, the quality of the resulting graphene as well as its structural and electrical characteristics strongly depend on the SiC face where growth has taken place. In this paper we use the density functional theory to analyze the structural and electronic properties of epitaxial graphene grown on three different SiC planes. Calculations are presented for the (6√3×6√3)R30°-reconstructed SiC(0001) surface (Si face) as well as the nonpolar SiC(11-20) and SiC(1-100) planes. We argue that the formation of a strongly-bound interface buffer layer is an exclusive property of the SiC(0001) surface. Moreover, our results indicate that nonpolar planes give rise to graphene with a nearly ideal low-energy spectrum.

THEORETICAL STUDY OF THE BAND GAP OF SrSe AND SrTe IN GW APPROXIMATION

2011 ◽  
Vol 25 (23) ◽  
pp. 1905-1914
Author(s):  
XIAO LING ZHU ◽  
HONG ZHANG ◽  
XIN LU CHENG
Keyword(s):  
Band Gap ◽  
Density Functional ◽  
Theoretical Study ◽  
Generalized Gradient ◽  
Gw Approximation ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties ◽  
Experimental Values ◽  
Interaction Approximation

Using the first-principles pseudopotential method within a generalized gradient approximation of the density functional theory, the structural and electronic properties of SrSe and SrTe have been studied. The calculated lattice parameters are in excellent agreement with experimental values, whereas the error in the minimum gap value is as high as 43.25% in SrSe . To get reliable band gap values of SrSe and SrTe , we employ the GW (G is the Green's function and W is the screened Coulomb interaction) approximation method. The result in GW approximation improves the band gap value of the SrSe greatly and agrees with the value of experimental measurement.

scholarly journals Unified Assessment of the Effects of Van der Waals Interactions on the Structural and Electronic Properties of Some Layered Organic Solids κ-(BEDT-TTF)2X

Crystals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 348
Author(s):  
Predrag Lazić ◽  
Ognjen Milat ◽  
Branko Gumhalter ◽  
Silvia Tomić
Keyword(s):  
Density Functional ◽  
Van Der Waals ◽  
Detailed Examination ◽  
Test System ◽  
Van Der Waals Interactions ◽  
Electronic Band ◽  
Prototype Test ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties ◽  
Experimental Crystal

Proper inclusion of van der Waals interactions (vdW) in ab initio calculations based on the density functional theory (DFT) is crucial to describe soft, organic, layered solids such as κ -(BEDT-TTF) 2 X . Since no consensus has been reached on the reliability of available vdW DFT functionals, most of the first principles calculations have been based on experimental crystal structure data without any structural optimization. Here, we explore optimal DFT-based schemes that account for the effects of vdW interactions on the structural and electronic band properties of three paradigmatic charge transfer salts, κ -(BEDT-TTF) 2 Cu 2 (CN) 3 , κ -(BEDT-TTF) 2 Ag 2 (CN) 3 , and κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl, for which a unified optimization of the structure is possible. Detailed examination of the prototype test system κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl shows that the optB88-vdW functional performs slightly better than the PBE-vdW and that the choice of pseudopotentials is critical to obtaining realistic results.

scholarly journals On the Use of DFT+U to Describe the Electronic Structure of TiO2 Nanoparticles: (TiO2)35 as a Case Study

2020 ◽  
Author(s):  
Angel Morales ◽  
Stephen Rhatigan ◽  
Michael Nolan ◽  
Frances Illas
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Plane Waves ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties ◽  
Rotationally Invariant

One of the main drawbacks in the density functional theory (DFT) formalism is the underestimation of the energy gaps in semiconducting materials. The combination of DFT with an explicit treatment of electronic correlation with a Hubbard-like model, known as DFT+<i>U</i> method, has been extensively applied to open up the energy gap in materials. Here, we introduce a systematic study where the selection of <i>U</i> parameter is analyzed considering two different basis sets: plane-waves (PWs) and numerical atomic orbitals (NAOs), together with different implementations for including <i>U</i>, to investigate the structural and electronic properties of a well-defined bipyramidal (TiO<sub>2</sub>)<sub>35 </sub>nanoparticle (NP). This study reveals, as expected, that a certain <i>U</i> value can reproduce the experimental value for the energy gap. However, there is a high dependence on the choice of basis set and, and on the +<i>U</i> parameter employed. The present study shows that the linear combination of the NAO basis functions, as implemented in FHI-aims, requires a lower <i>U</i> value than the simplified rotationally invariant approaches as implemented in VASP. Therefore, the transferability of <i>U</i> values between codes is unfeasible and not recommended, demanding initial benchmark studies for the property of interest as a reference to determine the appropriate value of <i>U</i>.

scholarly journals Cerium-Doped Endohedral Fullerene: A Density-Functional Theory Study

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
A. Z. AlZahrani
Keyword(s):  
Density Functional Theory ◽  
Total Energy ◽  
Density Functional ◽  
Structural Parameters ◽  
Repulsive Interaction ◽  
Total Density ◽  
Generalized Gradient ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Structural And Electronic Properties

First-principles total energy calculations of the structural and electronic properties of Ce-doped fullerene have been performed within the framework of the density functional theory at the generalized gradient approximation level. Among various locations, Ce atom was found to engage with the six-fold carbon ring. The total energy is found to significantly change as the Ce atom being shifted from the center of the cage toward the edge close to the six-membered ring where the total energy reaches its local minimum. Moreover, repulsive interaction between Ce atom and the cage components turns as the adatom directly interacts with the six C atoms of the ring. The lowest-energy CeC60 geometry is found to have a binding energy of approximately 5.34 eV, suggesting strong interaction of the dopant with the cage members. Furthermore, fundamental key structural parameters and the total density of states of the optimized structure have been determined and compared with the available data.

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