scholarly journals Dipole Polarizability of C28 and its Counterparts Nb4B18 and Ta4B18. Insights from a Density Functional Theory (DFT) Endeavour

2021 ◽  
Vol 2090 (1) ◽  
pp. 012172
Author(s):  
Demetrios Xenides ◽  
Panaghiotis Karamanis
Keyword(s):  
Electron Correlation ◽  
Scientific Community ◽  
Density Functional ◽  
Preliminary Investigation ◽  
Dipole Polarizability ◽  
Density Functionals ◽  
Target Species ◽  
Functional Theory ◽  
Hartree Fock ◽  
Smooth Convergence

Abstract We report on a preliminary investigation of the non linear optical (NLO) properties and in particular dipole polarizability. The target species are two perfect tetrahedral nanoclusters Nb4B18 and Ta4B18, along with their nanofullerene counterpart that is C28. Our study based on density functionals (DFs) that have gained popularity among the scientific community. In addition we performed Hartree-Fock calculations known for not including dynamic electron correlation. The DF obtained values are characterized by some dispersion, with maximal differences to be around 5 %, in all three cases. Given that the DFT introduces a fuzzy percentage of electron correlation sets the observed convergence of HF values to DFT ones is at least surprising. Furthermore, it should be said that though the values can be characterized as accurate their reliability should not be taken for granted. Last, we note the smooth convergence of LC-BLYP, LC-BP86, LC-BPW91 to LC-whPBE.

scholarly journals The crystalline structure of SrRuO3: Application of hybrid scheme to the density functionals revised for solids

2017 ◽  
Vol 57 (2) ◽  
Author(s):  
Šarūnas Masys ◽  
Valdas Jonauskas
Keyword(s):  
Crystalline Structure ◽  
Density Functional ◽  
Theoretical Modelling ◽  
Density Functionals ◽  
Hybrid Scheme ◽  
Generalized Gradient ◽  
Functional Theory ◽  
Hartree Fock ◽  
Hybrid Density Functional ◽  
Theory Scheme

The crystalline structure of ground-state orthorhombic SrRuO3 is reproduced by applying the hybrid density functional theory scheme to the functionals based on the revised generalized-gradient approximations for solidstate calculations. The amount of Hartree–Fock (HF) exchange energy is varied in the range of 5–20% in order to systematically ascertain the optimum value of HF mixing which in turn ensures the best correspondence to the experimental measurements. Such investigation allows one to expand the set of tools that could be used for the efficient theoretical modelling of, for example, only recently stabilized phases of SrRuO3, helping to resolve issues emerging for the experimentalists.

scholarly journals Covariant density functional theory: predictive power and first attempts of a microscopic derivation

2018 ◽  
Vol 178 ◽  
pp. 02001
Author(s):  
Peter Ring
Keyword(s):  
Nuclear Matter ◽  
Density Functional ◽  
Predictive Power ◽  
Tensor Force ◽  
Density Functionals ◽  
Functional Theory ◽  
Hartree Fock ◽  
Microscopic Derivation ◽  
Nuclear Systems ◽  
Covariant Density

We discuss systematic global investigations with modern covariant density functionals. The number of their phenomenological parameters can be reduced considerable by using microscopic input from ab-initio calculations in nuclear matter. The size of the tensor force is still an open problem. Therefore we use the first full relativistic Brueckner-Hartree-Fock calculations in finite nuclear systems in order to study properties of such functionals, which cannot be obtained from nuclear matter calculations.

scholarly journals TREATMENTS OF THE EXCHANGE ENERGY IN DENSITY-FUNCTIONAL THEORY

2008 ◽  
Vol 22 (14) ◽  
pp. 2225-2239
Author(s):  
TAMÁS GÁL
Keyword(s):  
Density Functional Theory ◽  
Ground State ◽  
Density Functional ◽  
Common Ground ◽  
Particle Density ◽  
Exchange Energy ◽  
Density Functionals ◽  
Simple Derivation ◽  
Functional Theory ◽  
Hartree Fock

Following a recent work [Gál, Phys. Rev. A64, 062503 (2001)], a simple derivation of the density-functional correction of the Hartree–Fock equations, the Hartree–Fock–Kohn–Sham equations, is presented, completing an integrated view of quantum mechanical theories, in which the Kohn–Sham equations, the Hartree–Fock–Kohn–Sham equations and the ground-state Schrödinger equation formally stem from a common ground: density-functional theory, through its Euler equation for the ground-state density. Along similar lines, the Kohn–Sham formulation of the Hartree–Fock approach is also considered. Further, it is pointed out that the exchange energy of density-functional theory built from the Kohn–Sham orbitals can be given by degree-two homogeneous N-particle density functionals (N = 1, 2, …), forming a sequence of degree-two homogeneous exchange-energy density functionals, the first element of which is minus the classical Coulomb-repulsion energy functional.

scholarly journals Theoretical Diagnostics of Second and Third-order Hyperpolarizabilities of Several Acid Derivatives

2019 ◽  
Vol 17 (1) ◽  
pp. 151-156 ◽  
Author(s):  
A. Karakas ◽  
Y. Ceylan ◽  
M. Karakaya ◽  
M. Taser ◽  
B. B. Terlemez ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Density Functional ◽  
Band Gaps ◽  
Dipole Polarizability ◽  
Third Order ◽  
Functional Theory ◽  
Hartree Fock ◽  
The Density Functional Theory ◽  
Similar Materials ◽  
Alpha Beta

AbstractThe density functional theory (DFT) at B3LYP/6-31G(d) level has been utilized to achieve the electric dipole moment $\left( \mu \right),$static dipole polarizability $\left( \alpha \right)$and first hyperpolarizability $\left( \beta \right)$values for ferulic acid (1) and chenodeoxycholic acid (2). The time-dependent Hartree-Fock (TDHF) technique as a powerful quantum chemical method has been implemented to reveal the dynamic $\alpha ,\,\beta $and third-order hyperpolarizabilities $\left( \gamma \right)$of the examined compounds. Our computational conclusions have been compared with the results of similar materials in the literature. The first and second frontier molecular orbitals (MOs) and their band gaps have also been investigated by means of DFT.

scholarly journals One-photon Absorption Characterizations, Dipole Polarizabilities and Second Hyperpolarizabilities of Chlorophyll a and Crocin

2018 ◽  
Vol 16 (1) ◽  
pp. 1242-1247
Author(s):  
A. Karakas ◽  
Y. Ceylan ◽  
M. Karakaya ◽  
M. Taser ◽  
B. B. Terlemez ◽  
...  
Keyword(s):  
Chlorophyll A ◽  
Quantum Chemical ◽  
Density Functional ◽  
Photon Absorption ◽  
Dipole Polarizability ◽  
Third Order ◽  
Functional Theory ◽  
Hartree Fock ◽  
Zero Values ◽  
Dipole Polarizabilities

AbstractThe dispersion-free dipole polarizability (α) computations for chlorophyll a (1) and crocin (2) have been achieved by density functional theory (DFT) at B3LYP/ 6-31G(d) level. The measured one-photon absorption (OPA) wavelengths are quite consistence with the theoretically obtained values. Ab-initio quantum chemical calculations (time-dependent Hartree-Fock (TDHF)) have been implemented to reveal the static second hyperpolarizabilities (γ) and dynamic dipole polarizabilities of the title molecules. The examined compounds display γ with non-zero values, introducing their third-order nonlinear optical (NLO) phenomena. The first and second frontier molecular orbitals of the investigated molecules have been also derived from DFT.

scholarly journals Electronic Structure Theory for X-Ray Absorption and Photoemission Spectroscopy

2021 ◽  
pp. 63-81
Author(s):  
Peter Krüger
Keyword(s):  
Electronic Structure ◽  
Electron Correlation ◽  
Density Functional ◽  
Electronic Structure Theory ◽  
Structure Theory ◽  
Photoemission Spectroscopy ◽  
Functional Theory ◽  
X Ray ◽  
Hartree Fock ◽  
X Ray Absorption

AbstractThe principles of X-ray absorption and photoemission spectroscopy calculations are introduced and the basics of electronic structure theory, including the Hartree–Fock approximation, density functional theory, its time-dependent version and quasiparticle theory are reviewed on an elementary level. Emphasis is put on polarization effects and the role played by electron correlation.

scholarly journals A Comparative Study of Oxygen and Hydrogen Adsorption on Strained and Alloy-Supported Pt(111) Monolayers

2021 ◽  
Vol 7 (7) ◽  
pp. 101
Author(s):  
Ian Shuttleworth
Keyword(s):  
Comparative Study ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
Binding Energies ◽  
High Symmetry ◽  
Density Functionals ◽  
Functional Theory ◽  
Ligand Effects ◽  
Ferromagnetic Alloys ◽  
Depth Study

A comparative study of the unreacted and reacted uniaxially strained Pt(111) and the layered (111)-Pt/Ni/Pt3Ni and (111)-Pt/Ni/PtNi3 surfaces has been performed using density functional theory (DFT). An in-depth study of the unreacted surfaces has been performed to evaluate the importance of geometric, magnetic and ligand effects in determining the reactivity of these different Pt surfaces. An analysis of the binding energies of oxygen and hydrogen over the high-symmetry binding positions of all surfaces has been performed. The study has shown that O and H tend to bind more strongly to the (111)-Pt/Ni/Pt3Ni surface and less strongly to the (111)-Pt/Ni/PtNi3 surface compared to binding on the equivalently strained Pt(111) surfaces. Changes in the surface magnetisation of the surfaces overlaying the ferromagnetic alloys during adsorption are discussed, as well as the behaviour of the d-band centre across all surfaces, to evaluate the potential mechanisms for these differences in binding. An accompanying comparison of the accessible density functionals has been included to estimate the error in the computational binding energies.

scholarly journals Unraveling the electrochemical and spectroscopic properties of neutral and negatively charged perylene tetraethylesters

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Christian Wiebeler ◽  
Joachim Vollbrecht ◽  
Adam Neuba ◽  
Heinz-Siegfried Kitzerow ◽  
Stefan Schumacher
Keyword(s):  
Absorption Spectra ◽  
Density Functional ◽  
Energy Levels ◽  
Spectroscopic Properties ◽  
Absorption Bands ◽  
Functional Theory ◽  
Vertical Excitation ◽  
Hartree Fock ◽  
Tauc Plot ◽  
Electrochemical Approach

AbstractA detailed investigation of the energy levels of perylene-3,4,9,10-tetracarboxylic tetraethylester as a representative compound for the whole family of perylene esters was performed. It was revealed via electrochemical measurements that one oxidation and two reductions take place. The bandgaps determined via the electrochemical approach are in good agreement with the optical bandgap obtained from the absorption spectra via a Tauc plot. In addition, absorption spectra in dependence of the electrochemical potential were the basis for extensive quantum-chemical calculations of the neutral, monoanionic, and dianionic molecules. For this purpose, calculations based on density functional theory were compared with post-Hartree–Fock methods and the CAM-B3LYP functional proved to be the most reliable choice for the calculation of absorption spectra. Furthermore, spectral features found experimentally could be reproduced with vibronic calculations and allowed to understand their origins. In particular, the two lowest energy absorption bands of the anion are not caused by absorption of two distinct electronic states, which might have been expected from vertical excitation calculations, but both states exhibit a strong vibronic progression resulting in contributions to both bands.

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