DFT calculation Research Papers - Academia.edu (original) (raw)

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- Organic Chemistry, Crystal structure, X Rays, DFT calculation

A controllable composition and morphology AuAg/ZnO catalyst, prepared by an easily scalable method, was, for the first time, explored for the electrocatalytic reduction of CO 2. It was found that the composition of the bimetallic alloy contributes to the overall CO 2 reduction performance. In particular, as also demonstrated by density functional theory calculations, CO production increases, decreasing the Au content in the catalyst alloy. The experimental investigation reveals that the products are H 2 and CO, which production rate increases in the presence of ZnO, up to a Faradic efficiency of 94.7 % at 0.4 V. On the other hand, controlling the oleic acid covering it is possible to modulate the surface properties allowing to obtain, at 0.6 V, H 2 /CO ratios equal to 1.1 and 1.9 for nanocatalysts thermally treated for 2 and 5 h, respectively.

- by Eleonora PONTICORVO
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- Electrochemistry, Nanomaterials, Nanotechnology, CO2 capture and storage
- by Aaron Marquez
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- DFT calculation

The synthesis and characterization of some new terphenyl ligands, modified by meta alkyl substitution on the central ring are described. The new ligands were designed for potential applications in the stabilization of novel low valent main group species or transition metal heteronuclear multiply bonded compounds. Compounds 1-I-C6H1-2,6-Ph2-3,5-Pr2i (1), 1-I-C6H1-2,6-Mes2-3,5-Pr2i (3) (Mes=2,4,6-trimethylphenyl), 1-I-C6H1-2,6-Trip2-3,5-Pr2i (5) (Trip=2,4,6-triisopropylphenyl) and 1-I-C6H1-2,6-Dipp2-3,5-Pr2i (6) (Dipp=2,6-diisopropylphenyl) were obtained

- by Didier Villemin
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- DFT calculation, Gibbs Free Energy, Methane, Solvent Effect
- by Dheeraj Singh
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- Raman Spectroscopy, Molecular, DFT calculation, Normal Modes
- by Jesus Graciani and +1
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- DFT calculation, Physical sciences, Nitrogen, CHEMICAL SCIENCES

"This paper introduces the theory and hardware implementation of two new algorithms for computing a single component of the discrete Fourier transform. In terms of multiplicative complexity, both algorithms are more efficient, in... more

"This paper introduces the theory and hardware implementation of two new algorithms for computing a single component of the discrete Fourier transform.
In terms of multiplicative complexity, both algorithms are more efficient, in general, than the well known Goertzel Algorithm."

- by h.m. de oliveira
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- Telecommunications Engineering, Signal Processing, Algorithm, DFT calculation
- by M. Ziolek
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- Engineering, Chemistry, FTIR spectroscopy, DFT calculation

The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We report the results of a community-wide effort that compared 15 solid-state codes, using 40 different potentials or basis set types, to assess the quality of the Perdew-Burke-Ernzerhof equations of state for 71 elemental crystals. We conclude that predictions from recent codes and pseudopotentials agree very well, with pairwise differences that are comparable to those between different high-precision experiments. Older methods, however, have less precise agreement. Our benchmark provides a framework for users and developers to document the precision of new applications and methodological improvements.

- by Gian-marco Rignanese
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- Science, Multidisciplinary, DFT calculation, Pseudopotentials
- by Hari Panicker
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- Analytical Chemistry, Quantum Chemistry, Raman Spectroscopy, Molecular

In this study, a different class of high nitrogen content ionic liquids were designed. The physicochemical properties of [DMT][4-XPhSO3], (X = NH2, OH, H, F, Br, CHO, CF3, CN and NO2) IPs based on the triazolium cation and substituted benzene sulfonate anions were fully investigated using M06–2X functional in conjunction with the aug-ccpvdz basis set. For all of the designed ILs the structural parameters, interaction energy between constructing parts, enthalpy of formation, natural charges and topological properties were calculated and discussed. The effect of the substituent change at anion part on the interaction energy and physicochemical properties is taking into account for the first time. As revealed from the results, the strength of the interaction between constructing ionic parts had a linear correlation with the electron content of the anionic part in a way that the more stable ion pairs with higher interaction energies constructed as the electron content of the anionic part increased. Melting point, critical-point temperature, electrochemical stability and conductivity which are some of the important IL,s characteristic physical properties were estimated, compared with each other and discussed with the help of the quantum chemical computationally obtained thermochemical data for nine designed various X substituted [DMT][4-XPhSO3] ILs. Finally, the enthalpy and Gibbs free energy of the formation for nine various substituted anions were calculated.

To understand the relationship between the electronic structure of amphetamines and their biological activity, a computational investigation was carried out to characterise the 17 O and 14 N, electric field gradient (EFG) tensors and nuclear quadrupole coupling constants (NQCC) as well as 17 O, 15 N, 13 C and 1 H chemical shielding tensors of amphetamines. Calculation were performed with the B3LYP and PW91P86 density functional theory (DFT) methods with the 6-311++G(d,p) basis set. The anisotropic (∆σ) and isotropic (σ iso) shielding are in good agreement with the available experimental data. The results indicate that the EFG and σ at oxygen are insensitive to substitution at the N and C 10 positions in amphetamines. In contrast, the nitrogen EFG and σ are quite sensitive towards substituent changes. Furthermore, it was found that EFG tensors are more sensitive than σ tensor to the electron density distribution in amphetamines. Biological activities of amphetamines were found to depend upon the electron density distribution in the region of N atoms. Reference to this paper should be made as follows: Ebrahimi, Z.F. and Wilson, D.J.D. (2015) 'DFT investigation of the electronic structure of amphetamines: effect of substituent on O and N chemical shielding and electric field gradient tensors', Int.

- by zahra fallah ebrahimi
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- DFT calculation
- by Zhaosheng Li
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- Engineering, Materials Engineering, Condensed Matter Physics, Inorganic Chemistry
- by Marcello Picollo
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- Chemistry, Vibrational Spectroscopy, Solid State NMR, DFT calculation

The activation of CO2 and its hydrogenation to methanol are of much interest as a way to utilize captured CO2. Here, we investigate the use of size-selected Cu4 clusters supported on Al2O3 thin films for CO2 reduction in the presence of hydrogen. The catalytic activity was measured under near-atmospheric reaction conditions with a low CO2 partial pressure, and the oxidation state of the clusters was investigated by in situ grazing incidence X-ray absorption spectroscopy. The results indicate that size-selected Cu4 clusters are the most active low-pressure catalyst for catalytic CO2 conversion to CH3OH. Density functional theory calculations reveal that Cu4 clusters have a low activation barrier for conversion of CO2 to CH3OH. This study suggests that small Cu clusters may be excellent and efficient catalysts for the recycling of released CO2.

- by Stefan Vajda
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- Chemistry, Medicine, DFT calculation, Transition metals
- by Marcin Brynda
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- Inorganic Chemistry, Organic Chemistry, Organometallic Chemistry, NMR Spectroscopy
- by Elena Pritchina
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- Density-functional theory, DFT calculation, Physical sciences, Time Resolved
- by Jailton Souza de Almeida
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- Physics, Solar Energy, DFT calculation
- by Prashant Deshlahra
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- Reaction Mechanisms, Catalysis, Spectroscopy, DFT calculation
- by Michel Rajzmann
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- Organic Chemistry, DFT calculation, DFT, HF

The solid phase FT-IR and FT-Raman, solution phase linear dichroism IR (in nematic liquid crystal), and vapor phase GC/IR spectra of 2-(methylthio)benzonitrile have been recorded in the regions 4000–50, 3500–100, 4000–400, and 4000–650 cm−1, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure optimizations and force field calculations based on density functional theory (DFT) using standard B3LYP/6-31G* and B3LYP/6-311+G** method and basis set combinations. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors yielding fairly good agreement between observed and calculated frequencies. IR dichroism data revealed an error in band assignment associated with a νCS vibration, which could be eliminated only by introducing independent scaling factors for sulfur, whereas the overall frequency fit was further improved. Simulation of infrared and Raman spectra utilizing...

- by Gábor Keresztury and +1
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- Density-functional theory, DFT calculation, Density Functional Theory, Case Study

We present a combined experimental and theoretical quantification of the adsorption enthalpies of seven organic molecules (acetone, acetonitrile, dichloromethane, ethanol, ethyl acetate, hexane, and toluene) on graphene. Adsorption enthalpies were measured by inverse gas chromatography and ranged from −5.9 kcal/mol for dichloromethane to −13.5 kcal/mol for toluene. The strength of interaction between graphene and the organic molecules was estimated by density functional theory (PBE, B97D, M06-2X, and optB88-vdW), wave function theory (MP2, SCS(MI)-MP2, MP2.5, MP2.X, and CCSD(T)), and empirical calculations (OPLS-AA) using two graphene models: coronene and infinite graphene. Symmetry-adapted perturbation theory calculations indicated that the interactions were governed by London dispersive forces (amounting to ∼60% of attractive interactions), even for the polar molecules. The results also showed that the adsorption enthalpies were largely controlled by the interaction energy. Adsorption enthalpies obtained from ab initio molecular dynamics employing non-local optB88-vdW functional were in excellent agreement with the experimental data, indicating that the functional can cover physical phenomena behind adsorption of organic molecules on graphene sufficiently well.

- by Frantisek Karlicky
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- Molecular Dynamics Simulation, Graphene, Adsorption, Ab initio calculations

The density-functional theory (DFT) is used to simulate clusters of the formula FenAsm. We optimize the bond lengths and angles to determine the stable structure for integer values of n and m. We calculate the vibrational frequencies for all of the clusters and hence determine the largest frequency of each cluster as a function of number of As atoms. For

- by Ahmad Nazrul Rosli
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- DFT calculation, Superconductors, Oscillations, Temperature measurement

This paper examines finite field trigonometry as a tool to construct digital trigonometric transforms. In particular, by using properties of k-cosine function over a Galois field, the finite field discrete cosine transform is introduced. The finite field DCT pair in GF(p) is defined, having blocklengths that are divisors of (p+1)/2. A special case is the Mersenne finite field DCT, defined when p is Mersenne prime. In this instance block lengths that are power of two are possible and radix-two fast algorithms can be used to compute the transform.

- by Ricardo Campello
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- Signal Processing, DFT calculation, Discrete Cosine Transform, Finite Fields
- by prateek tyagi
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- DFT calculation
- by MAURICIO ALCOLEA PALAFOX
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- Vibrational Spectroscopy, DFT calculation, Nucleic Acids
- by Daniel Rentsch
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- Engineering, Thermodynamics, Nuclear Magnetic Resonance, Hydrogen Storage

The role of various factors (structure, solvent, and relativistic treatment) was evaluated for square-planar 4d and 5d transition-metal complexes. The DFT approach for calculating the structures was calibrated using a cluster approach and compared to X-ray geometries, with the PBE0 functional (def2-TZVPP basis set) providing the best results, followed closely by the hybrid TPSSH and the MN12SX functional. Calculations of the NMR chemical shifts using the two-component (2c, Zeroth-Order Regular Approximation as implemented in the ADF package) and four-component (4c, Dirac-Coulomb as implemented in the ReSpect code) relativistic approaches were performed to analyze and demonstrate the importance of solvent corrections (2c) as well as a proper treatment of relativistic effects (4c). The importance of increased exact-exchange admixture in the functional (here PBE0) for reproducing the experimental data using the current implementation of the 2c approach is partly rationalized as a compensation for the missing exchange-correlation response kernel. The kernel contribution was identified to be about 15–20% of the spin-orbit-induced NMR chemical shift, ΔδSO, which roughly corresponds to an increase in ΔδSO introduced by the artificially increased exact-exchange admixture in the functional. Finally, the role of individual effects (geometry, solvent, relativity) to NMR chemical shift is discussed in selected complexes. Although a fully relativistic DFT approach is still awaiting the implementation of GIAOs for hybrid functionals and an implicit solvent model, it nevertheless provides reliable NMR chemical shift data at an affordable computational cost. It is expected to outperform 2c approach, in particular for the calculation of NMR parameters in heavy-element compounds.

- by Michal Repisky and +3
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- NMR Spectroscopy, Relativistic Quantum Chemistry, DFT calculation, Spin-Orbit Coupling
- by Jeffrey Harwell
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- Engineering, Materials Engineering, Analytical Chemistry, Technology

Raman spectroscopy has been used to investigate the α → β solid-solid phase transition of the energetic material hexahydro-1,3,5-trinitro-1,3,5- s-triazine (RDX) in real time. The thermal conversion of α → β at atmospheric pressure occurred at 477 K. Temperature-induced spectroscopic changes in the Raman spectrum of α-RDX, such as peak shifting and broadening and disappearance of spectral bands confirm the phase transition. For the interpretation of the experimental results, the structural and spectral characteristics of α- and β-RDX have been studied by performing DFT calculations for energies, geometries, vibrational frequencies and NMR shielding constants (CSGT method). The theoretical data, using density functional theory (DFT) approximation, and experimental results were consistent with each other. The results from these experiments show that once the β-RDX is formed by heating at slow rates, crystal transformation occurs near the melting point and no reversible change in the symmetry is observed. Moreover the differences in the Raman spectra of both solid phases are evident and persistent. In addition, the results of calculated and experimental NMR chemical shifts ( 13C and 15N) confirm the agreement between de AAA conformer and the β-RDX structure.

- by Ricardo Infante-castillo and +2
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- Raman Spectroscopy, Density-functional theory, Molecular, DFT calculation

In this paper, we explore the electric field gradients (EFGs) at 238U sites for antiferromagnetic UX2 (X ¼ P, As,
Sb, Bi) using LDA, LDA + U, GGA, GGA + U, and the exact exchange for correlated electrons schemes by
considering the diagonalization of the spin–orbit coupling Hamiltonian in the space of the scalar
relativistic eigenstates using the second-order variational procedure. The electronic structures and
magnetic properties of the compounds are also investigated. It is found that the density functional
theory approaches except exact exchange for correlated electrons are not successful in reproducing the
experimental zero electric field gradient value in UBi2, even LDA + U and GGA + U within their default 4f
density matrices by varying the U parameter in an energy interval of [0; 4 eV], though these techniques
with no need to manually adopt their initial conditions (elements of the occupation matrix) are effective
in the calculation of the nonzero electric field gradients for the other compounds. The exact exchange
for correlated electrons has efficiently provided a null electric field gradient in UBi2 and nonzero electric
field gradients for the other compounds by adjusting its dimensionless parameter a to 0.4. The physics
of the null electric field gradient in UBi2 is revealed in this article and it is discussed that the source of the
ignorable electric field gradient originates from the antiferromagnetic ordering of [Y as compared to the
long-range antiferromagnetic ordering of [[YY in the other compounds. Furthermore, our calculated
magnetic moments for the uranium atoms in these compounds are consistent with the available
experimentally measured values as compared to the severely underestimated theoretical results.

- by Iftikhar Ahmad and +2
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- Materials Engineering, Condensed Matter Physics, Materials Science, Density-functional theory
- by Abdelkader Kara
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- Engineering, Epitaxial Growth, Applied Physics, Density-functional theory
- by Vincent Aroulmoji
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- Physics, Chemistry, Pharmaceutical Chemistry, DFT calculation

We report results on the electronic, vibrational, and optical properties of SnO2 obtained using first-principles calculations performed within the density functional theory. All the calculated phonon frequencies, real and imaginary parts of complex dielectric function, the energy-loss spectrum, the refractive index, the extinction, and the absorption coefficients show good agreement with experimental results. Based on our calculations, the SnO2 electron and hole effective masses were found to be strongly anisotropic. The lattice contribution to the low-frequency region of the SnO2 dielectric function arising from optical phonons was also determined resulting the values of ɛ 1⊥latt(0) = 14.6 and ɛ 1∥latt(0) = 10.7 for directions perpendicular and parallel to the tetragonal c-axis, respectively. This is in excellent agreement with the available experimental data. After adding the electronic contribution to the lattice contribution, a total average value of ɛ1(0) = 18.2 is predicted for the static permittivity constant of SnO2.

- by Horacio Alves and +1
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- DFT calculation, SnO2, High dielectric constant, Lattice Dynamics

بسته محاسباتی کوانتوم اسپرسو

- by Arsalan Akhtar and +1
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- Density-functional theory, DFT calculation, Quantum-ESPRESSO
- by Theresa Hedderman
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- Engineering, Materials Engineering, Analytical Chemistry, Technology

In the present study, first-principles Density Functional Theory (DFT) with Generalized Gradient Approximation (GGA) is exploited to investi-gate different properties of AlB2 by using ultra-soft Pseudopotential technique. The study involves the calculations of the structural, mechanical, electron-ic, optical and thermodynamical properties of AlB2. All these properties are studied at ambient condition and at various temperatures and pressures. It is found that the volume decreases with increasing pressure. Our calculated elastic constants agree with the previous theoretical data expect for C12. and AlB2 is found to be brittle. Calculated electronic band structures are doubly degenerate along Γ-A direction. The total DOS curves of this compound shares similar free-electron-like metallic features. The B 2p states dominate the conductivity of AlB2. The reflectivity spectrum shows that the material is a good reflec-tor within the energy range, 8.15-20.65 eV and the materials should have no band gap. The static refractive index of AlB2 is found to have the values ~ 6.76. Debye temperature increase with pressure. The temperature dependence of α is very weak at higher temperatures and higher pressures.

- by Shabnaz Afrin and +1
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- Ab initio calculations, DFT calculation, DFT, first principles, 1st Principle Electronic Band Structure Calculation

Neste trabalho é introduzido um novo algoritmo, desenvolvido no ambiente Matlab, para realizar uma estimação dos coeficientes de uma série trigonométrica de Fourier, baseado no método dos mínimos quadrados seqüencial. São apresentadas... more

- by h.m. de oliveira
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- Algorithms, Fourier Analysis, DFT calculation, Fourier Series

Doxorubicin (DOXO) is a powerful anthracycline antibiotic used to treat many human neoplasms, including acute leukemias, lymphomas, stomach, breast and ovarian cancer, and bone tumors, yet causing cardiotoxicity at the same time. For this reason, there is a great interest in medical field to gain deep insight and knowledge of this molecule. Raman, Fourier Transform Infrared (FT-IR) absorption spectroscopy, and Resonance Raman scattering were performed for the vibrational characterization of DOXO molecule. Density function theorem (DFT) modeling of Raman and FT-IR spectra were used for the assignment of the vibrational frequencies. The optimized molecular structured was obtained, first, on the basis of potential energy distribution. The simulation for vibrational bands is based on the calculations for internal force constants and potential energy distribution matrices. The calculated DOXO vibrational bands show qualitative agreement with the experimental observations (FT-IR absorption and Raman scattering). Microsc. Res. Tech. 73:991–995, 2010. © 2010 Wiley-Liss, Inc.

- by Gobind Das
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- Raman Spectroscopy, Raman and IR microscopy, DFT calculation, Doxorubicin

Determination of experimental kinetic isotope effects (KIE) is one of the most useful tools for the exploration of reaction mecha- nisms in organometallic chemistry. The approach has been further strengthened during the last decade with advances in modern compu- tational chemistry. This allows for the calculation of a theoretical KIE that can often be compared directly to the experimental value. This combined experimental/theoretical approach can be particularly useful in cases where the value of the experimental KIE is not directly associat- ed with one particular reaction step (e.g., in a catalytic reaction). The approach is highlighted by using recent examples from both stoichio- metric and catalytic reactions, homogeneous and heterogeneous catal- ysis, and enzyme catalysis to illustrate the expected accuracy and utility of this approach.

- by Peter Fristrup
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- Chemical Kinetics, DFT calculation, Kinetic Isotope Effect

MP2 method and different functionals such as M06-HF, M06-2X, CAM-B3LYP, PBE0, B3LYP and M06L incorporating different XC amounts were used to calculate the static first hyperpolarizabilies β(0) of eight molecules which are derivatives of benzene, stilbene and diphenylacetylene. The values were then compared to the experimental ones. The M06-2X functional was then selected for further calculations. NBO calculations were also performed to define the intramolecular charge transfer in each molecule. TD-DFT calculations were performed taking into account the solvent effect using the IEF-PCM formalism. Some parameters characterizing the vertical transitions such as the wavelength of the maximum absorption λ max were compared to the experimental ones. Finally, solvation Gibbs free enthalpy ΔG solv values have also been examined in order to determine which the specific solvent for a given molecule is.

The band structures of three graphene derivatives (chlorographene, fluorographene, and graphane) were analyzed at three levels of many-body GW theory (G0W0, GW0, and GW) constructed over GGA (PBE) and screened hybrid HSE06 orbitals. DFT band gap values obtained with the HSE06 functional were notably larger than those from PBE calculations but were significantly lower than band gaps from all GW calculations. On the other hand, all GW-type calculations gave similar band gaps despite some differences in band structures. The band gap (4.9 eV at the highest GW-HSE06 level) was predicted to be smaller than that of fluorographene (8.3 eV) or graphane (6.2 eV). However, chlorographene can be considered a wide-band gap insulator analogous to fluorographene and graphane. Using the Bethe–Salpeter equation, optical absorptions of graphene derivatives were found to be at significantly lower energies due to large binding energies of excitons (1.3, 1.9, and 1.5 eV for chlorographene, fluorographene, and graphane, respectively). Point defects lowered band gaps and absorption energies. Taking into account the low concentration of defects in this type of material, their effect on the discussed electronic properties was rather small.

- by Huazhou Lv
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- Electrical Engineering, DFT calculation

This review aims to briefly outline the Hubbard-U scheme and to investigate the effect of its inclusion in standard Density Functional Theory on electronic, structural, and optical properties of ZnO wurtzite structure. To remedy the miscalculation of optimized lattice parameters determined by Local Density Approximation and Generalized Gradient Approximation approximations to experimental values, the effect of the implementation of Hubbard-U correction for only d state or for both d and p states was investigated for theoretical data collected from previous works. Further effort was devoted to studying the incorporation of U d,Zn and U p,O to reproduce correct band gap, to exploring various regions composed of valence and conduction bands and their origin, and to revealing the nature of chemical bonding. This review also provides graphical and tabulated values extracted from earlier works on optical properties of ZnO wurtzite structure. It summarizes the effect of U d,Zn and U p,O in several exchange-correlation functionals on the intensity and location of major peaks composed real and imaginary part of dielectric function as well as on the shift of main absorption peak and optical absorption edge. A comparison was made, wherever possible, between theoretical and experimental results.

- by Ahmad Azmin Mohamad
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- Electronics, DFT calculation, DFT, ZnO (Zinc Oxide)
- by Julian Del Campo
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- DFT calculation