LSDA Methods Research Articles

First principles investigation of structural, elastic, thermoelectric, electronic and optical properties XH3 (X=Ac, La) for hydrogen storage

Efficient hydrogen storage is essential for its use as an energy source. Considering the various methods, hydrogen storage in solid materials shows great promise but requires further research. This study employs density functional theory using the Wien2k, with the LSDA method to determine the stability of this storage mode, and LSDA + mBJ to calculate the electronic, optical, and thermoelectric properties of AcH3 and LaH3. The electronic properties reveal that XH3 (X = Ac, La) exhibits a semiconducting nature with indirect energy gaps in both cases. The analysis of hydrogen storage properties determined the gravimetric hydrogen storage capacities for AcH3 and LaH3 to be 1.297 and 2.086 wt%, respectively. Calculations of the elastic constants validated the mechanical stability of these compounds. Thermoelectric characteristics, including electrical and thermal conductivity, Seebeck coefficient, electronic specific heat capacity, and Pauli magnetic susceptibility, have been evaluated, highlighting their p-type characteristics. The figure of merit indicates their potential for thermoelectric devices. Gravimetric ratios suggest significant hydrogen storage capacity, which could contribute to various transportation and energy applications.

First principle investigation on properties of MnO2 as an electrode material for Li, Na, Mg, and Al -ion batteries

This study uses noble evaluations in Density Functional Theory (DFT) framework to investigate the structural, electrochemical, magnetic, and electrical properties of AMn2O4 (A = Li, Na, Mg, and Al) cathode materials for various metal-ion batteries. The calculations are performed by four DFT methods (GGA/+U, LSDA/+U). Considering volume change Both GGA and LSDA methods showed that NaMn2O4 had the highest and AlMn2O4 had the lowest volume reduction, caused by electronegativity of Al and the initial unit cell volume. The cell voltages were calculated with two different approaches called as internal and Fermi energy. It was concluded that the probable low cycle-ability of this family can be attributed to remarkable alteration of magnetic moment of manganese transition metal during extraction/insertion of intercalating ions. The electrical properties of AMn2O4 materials were investigated evaluating BGs and electrical rate-capability. For each material two kinds of band-gap (BG) and two criterions for rate-capability were considered, i.e. ILBG/ELBG, and Delta/CCTB, respectively. The BG evaluation showed that all the considered materials have appropriate conductivity. Both of the evaluated Delta and CCTB approaches predicted high rate-capability for the AMn2O4 materials. Our calculations demonstrated that MnO2 is a suitable and highly considerable cathode material for the Li and beyond-Li -ion batteries.

Synthesis, characterization and computational studies of 4-[(Pyridine-3-carbonyl)-hydrazonomethyl]-benzoic acid

A new hydrazone derivative compound, 4-[(Pyridine-3-carbonyl)-hydrazonomethyl]-benzoic acid, C15H11N3O, was obtained and characterized by 1H NMR, 13C NMR and UV–Vis, FT-IR and FT-Raman spectroscopy techniques. Molecular geometry, vibrational wavenumbers, frontier molecular orbital and non-linear optical (NLO) property of the title compound were calculated using ab initio Hartree-Fock (HF) and Density Functional Theory (DFT), employing B3LYP functional at 6–311++G (d,p) basis set. 1H and 13C NMR chemical shifts were calculated by using the gauge in dependent atomic orbital (GIAO) method at the HF and B3LYP methods with different basis sets. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were obtained from DFT LSDA methods with 6–311++G (d,p) basis set. The NLO behaviour of the title compound has been studied by determining the electric dipole moment (μ) and hyperpolarizability (β) using both B3LYP/6–311++G (d,p) and HF/6–311++G (d,p) methods. The energy gaps s(ΔEgap=ELUMO−EHOMO) of title molecule were calculated at 4.15, 2.77 and 9.81 eV with DFT-B3LYP/6–311++ G (d,p), DFT-LSDA/6–311++ G (d,p) and HF/6–311++ G (d,p) level of theory, respectively. The calculated experimentally energy gap was found as 2.827 eV.

Unraveling the electromagnetic structure of the epitaxial graphene buffer layer

We have employed density functional theory to study the structural, electronic and magnetic properties of the first all-carbon layer grown epitaxially on 6H-SiC(0 0 0 1). Using VDW-DF, M06-L, LSDA, LSDA+U, PBE and PBE-D2 methods we have performed a comparative study of the preferable magnetic configuration of the system. In this work, for the first time, we report a stable antiferromagnetic (AF) ordering in the buffer layer caused by the presence of silicon dangling bonds in the SiC top layer. This state is nearly degenerated with the ferromagnetic state with a magnetic moment equal to the number of silicon dangling bonds. A net magnetic moment of 0.55 µb per Si dangling bond was found for both states. However, only for the ferromagnetic state the carbon atoms of the buffer layer exhibited a magnetic moment. The magnetic configuration is much more stable than the non-polarized one and might explain SQUID results and spin transport experiments with epitaxial graphene. Furthermore, we found that, as previously observed experimentally, the buffer layer is a true semiconductor.

Electronic and magnetic properties of AFe2 (A=Zr, Hf, Lu) compounds in the cubic Laves phase

Electronic structures and magnetic properties of three Laves phase iron compounds (ZrFe2, HfFe2 and LuFe2) have been investigated by using full potential linear muffin-tin orbital (FP-LMTO) method within the local spin density approximation LSDA and LDA + U approach. In order to highlight the correlation effect, we have used the LSDA + U approach.The 3d -4d or 3d -5d exchange interactions between Fe and Zr, or Fe and (Hf, Lu) electrons lead to the anti-parallel coupling for Fe (3d) and Zr (4d), or Fe (3d) and (Hf (5d), Lu (5d)) states. In particular this latter approach compared to LSDA method accurately describes the effect of hybridization.The results obtained agree well with other experimental works. We derived the bulk and shear moduli, Young's modulus, and Poisson's ratio. The Debye temperature of ZrFe2, HfFe2 and LuFe2 was estimated from the average sound velocity.

DFT, RHF and MP2 based study of the thermodynamic, electronic and non-optical properties of DNA nucleobases

Deoxyribonucleic acid or DNA is a molecule that contains the instructions an organism needs to develop, live and reproduce. These instructions are found inside every cell, and are passed down from parents to their children. In this study, the DNA nucleobases, that is. Adenine (A), Guanine (G), Cytosine(C) and Thymine (T) have been investigated by employing quantum chemical methods calculation. The thermodynamic parameters such as entropy, enthalpy, heat capacity and zero point vibrationional energy, non optical linear properties (dipole moment and mean polarizability) and Mullikan charges were calculated using Restricted Hartree–Fock (RHF), Moller-Plesset Second Order Perturbation Theory (MP2) and Density FuTheory (DFT), B3LYP and LSDA methods with 3- 21G, 3-21+G and 6-31G basis set . In addition, HOMO-LUMO energy gap of each of the molecules was calculated. The high value of HOMO-LUMO energy gap indicates the high stability of the molecules in chemical reaction. Of the four molecules, guanine has the highest value of HOMO- LUMO energy gap which implies that it is the most stable molecule in chemical reaction. The values of the dipole moment obtained were in agreement with the experimental values. For instance, the dipole moment of guanine at B3LYP/6-31G was calculated as 7.2D while the experimental value is 7.1D. Gaussian 03 package was used to perform all the calculations. Results from comparison of the DFT, MP2 and RHF methods shows close results and can be seen to support one another. Keywords: DNA, Nucleobases, HOMO-LUMO, DFT, RHF and MP2

Vibrational Analysis and NLO Impact of Coordinate Covalent Bond on Bis (Thiourea) Cadmium Bromide: A Comparative Computational Study

In the present research work, the thorough experimental and theoretical investigation is made on the crystal compound; Bis (thiourea) Cadmium Bromide (BTCB) by recording FT-IR, FT-Raman and UV Visible spectra. The computational calculations are carried out by HF, CAM-B3LYP, DFT (B3LYP and B3PW91) and LSDA methods with 3-21 G (d, p) basis sets and the corresponding results were tabulated. The compound belongs to orthorhombic crystal class with space group of Pn21a and point group of symmetry C2v. The NLO properties have been studied by calculating average Polarizability and diagonal hyperpolarizability. The physical and chemical properties of the coordination complex due to the Vander Waals link are found to be enriched. The thermodynamical parameters of TGA and DSC are compared with calculated values obtained from NIST thermodynamical program. The variation of specific heat capacity, entropy and enthalpy with respect to different temperature are displayed in the graph and are discussed.

A study of the molecular, vibrational, electronic and quantum chemical investigation of 2-methyl-1-vinylimidazole

The spectroscopic properties of 2-methyl-1-vinylimidazole (abbreviated as 2M1VIM) were examined by FT-IR, FT-Raman and NMR techniques. FT-IR and FT-Raman spectra were recorded in the region 4000–400cm−1 and 3500–50cm−1, respectively. The 1H and 13C NMR spectra were recorded in CDCl3. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional theory (DFT) employing B3LYP and LSDA methods with 6-311++G(d,p) basis set. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibration were assigned on the basis of potential energy distribution (PED) of the vibrational modes calculated with scaled quantum mechanical (SQM) method. The optimized structure of the compound was interpreted and compared with the reported experimental values. The observed vibrational ware numbers, absorption wavelengths and chemical shifts were compared with calculated values. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. As a result, the optimized geometry, and calculated spectroscopic data show a good agreement with the experimental results.

Conformational stability, molecular orbital studies (chemical hardness and potential), vibrational investigation and theoretical NBO analysis of 4-tert-butyl-3-methoxy-2,6-dinitrotoluene

The FT-IR and FT-Raman spectra of 4-tert-butyl-3-methoxy-2,6-dinitrotoluene (musk ambrette) have been recorded in the regions 4000–400cm−1 and 3500–100cm−1, respectively. The total energy calculations of musk ambrette were tried for the possible conformers. The molecular structure, geometry optimization, vibrational frequencies were obtained by the density functional theory (DFT) using B3LYP and LSDA method with 6-311G(d,p) basis set for the most stable conformer “C1”. The complete assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes, calculated and the scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. The stability of the molecule arising from hyper conjugate interactions and the charge delocalization has been analyzed using bond orbital (NBO) analysis. The HOMO and LUMO energy gap reveals that the energy gap reflects the chemical activity of the molecule. The dipole moment (μ), polarizability (α), anisotropy polarizability (Δα) and first hyperpolarizability (βtot) of the molecule have been reported. The thermodynamic functions (heat capacity, entropy and enthalpy) were obtained for the range of temperature 100–1000K. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP).

Structural study, NCA, FT-IR, FT-Raman spectral investigations, NBO analysis and thermodynamic properties of 2′,4′-difluoroacetophenone by HF and DFT calculations

In this work, the vibrational spectral analysis was carried out by FT-IR and FT-Raman spectroscopy in the regions of 4000–400cm−1 and 3500–100cm−1, respectively for 2′,4′-difluoroacetophenone (DFAP). The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on Hartree–Fock (HF), density functional theory (DFT) using B3LYP and LSDA methods with 6-31G basis set combination. The mixing of the fundamental modes was determined with the help of potential energy distribution (PED). The energies of the frontier molecular orbitals have also been determined. Complete NBO analysis was also carried out using B3LYP/6-31G level of theory to find out the intramolecular electronic interactions and their stabilization energy. Thermodynamic properties of the title compound were calculated at the different temperature. Finally, the calculation results were applied to simulate FT-IR and FT-Raman spectra of the title compound which show good agreement with observed spectra.

Comparison of computational methods in the electronic structure of carbon nanotubes of single walled (8,0)

The carbon nanotubes have attracted much interest for their electronic properties which go from metallic to semiconducting behavior, depending both on diameter, number of layers and chirality. The value of their band gap is obviously a crucial point to be addressed because it enters in the nanbotube application as microelectronic devices. This work was developed through an estimate of the behavior of the electronic structure of carbon nanotubes of single walled 8,0 and the assessment of electrical conduction through various methodologies such as LSDA, B3PW91, B3LYP and HF ab initio methods and PM3 and AM1semi-empirical methods. The methods showed similarities with the geometrical parameters reported in the literature. The hybrid methods based on density functional generated a good approximation in the energy gap value of single-walled carbon nanotubes 8,0. Results will be presented.

Vibrational frequencies, structural confirmation stability and HOMO–LUMO analysis of nicotinic acid ethyl ester with experimental (FT-IR and FT-Raman) techniques and quantum mechanical calculations

Abstract The FT-IR and FT-Raman spectra of nicotinic acid ethyl ester (abbreviated as NAEE, C 8 H 9 NO 2 ) have been recorded in the region 3600–10 cm −1 . Potential energy curve was computed by means of scanning CCC O torsion angle. The optimized geometric parameters geometry optimization and the energies associated possible two conformers (C1 and C2) were computed. The computational results diagnose the most stable conformer of NAEE as the C1 form. The optimum molecular geometries, energies, normal mode wavenumbers, infrared and Raman intensities, corresponding vibrational assignments, atomic charges, HOMO–LUMO analysis and thermo-dynamical parameters were investigated with the help of HF, B3LYP and LSDA methods with 6-311G(d,p) and 6-311G++(d,p) basis sets. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanics (SQM) method. Thermodynamic properties of the title compound at different temperatures were calculated. The results of the calculations were applied to simulate infrared and Raman spectra of the title compound which show excellent agreement with the observed spectra.

Electronic and magnetic structure of BaCoO2 as obtained from LSDA and [formula omitted] calculations

Density functional theory is used to study the structural, electronic, and magnetic properties of BaCoO2. Structural relaxation for different collinear magnetic configurations points to a remarkable magneto-elastic coupling in BaCoO2. Although we obtain several stable long range ordered magnetic structures, ferromagnetism is energetically favorable in the case of the LSDA method. In contrast, for the LSDA+U method antiferromagnetic ordering is found to be favorable.

First-principles study of crystal structural stability and electronic and magnetic properties inLaMn7O12

The crystal structure, electronic and magnetic properties ofLaMn7O12 ((LaMn33 + )AMn43 + O12) are investigated byGGA (LSDA) and GGA + U (LSDA + U) (0.0 ≤ U ≤ 5.0 eV)methods. Based on two experimentally refined structures (distinguished by the distortion parameterΔ, namelySI (Δ = 8.5 × 10 − 5) andSII (Δ = 25.0 × 10 − 4)), GGAand GGA + U withU < 3.0 eV calculationsindicate that SI with a small distortion is the lowest-energy crystal structure whileGGA + U with3.0 ≤ U ≤ 5.0 eV calculationsshow that SII with a larger distortion is the ground-state crystal structure. Within the LSDA method,SII is always the ground-state structure no matter ifU is considered or not. There are two independent magnetic sublattices:Mn3 + within theA site and Mn3 + within the B site. First, it is predicted that A-siteMn3 + ions are preferably AFM-coupled in G-type (antiferromagnetically coupled in threedirections). Based on this result, four magnetic configurations (FM-, AFM1-, AFM2- and AFM3-) are designed, and their total energies are calculated. Our results demonstratethat AFM2 and AFM3 are the lowest magnetic state, respectively, forSI andSII. Correspondingly,LaMn7O12 is metallic with no orbital ordering at AFM2 forSI while it is an insulator with orbital ordering at AFM3 forSII. Thus, modulation of the distortion parameterΔ, e.g. by chemical doping, could be employed as a new avenue to induce amagnetic phase transition and the corresponding metal-to-insulator transition inLaMn7O12.

Chemical trend of exchange coupling in diluted magnetic II-VI semiconductors:Ab initiocalculations

We have calculated the chemical trend of magnetic exchange parameters ($J_{dd}$, $N \alpha$, and $N \beta$) of Zn-based II-VI semiconductors ZnA (A=O, S, Se, and Te) doped with Co or Mn. We show that a proper treatment of electron correlations by the LSDA+$U$ method leads to good agreement between experimental and theoretical values of the nearest-neighbor exchange coupling $J_{dd}$ between localized 3$d$ spins in contrast to the LSDA method. The exchange couplings between localized spins and doped electrons in the conduction band $N \alpha$ are in good agreement with experiment as well. But the values for $N \beta$ (coupling to doped holes in the valence band) indicate a cross-over from weak coupling (for A=Te and Se) to strong coupling (for A=O) and a localized hole state in ZnO:Mn. That hole localization explains the apparent discrepancy between photoemission and magneto-optical data for ZnO:Mn.

Study on the ground state of NiO: The LSDA (GGA)+U method

Abstract The ground-state properties of NiO have been investigated using the all-electron full-potential linearized augmented plane wave (FLAPW) and the so-called LSDA (GGA)+ U (LSDA—local-spin-density approximation; GGA—generalized gradient approximation) method. The calculated result indicates that our estimation of U is in good agreement with experimental data. It is also found that none of the LSDA (GGA) methods is able to provide, at the same time, accurate electronic and structural properties of NiO. Although the GGA+ U method can properly predict the electronic band gap, it overestimates the lattice constant and underestimates the bulk modulus. Then only the LSDA+ U method accurately reports the electronic and structural properties of NiO. The calculated band gap and the density of states (DOS) show that the material NiO is the charge-transfer insulator, which agrees with the spectroscopy data. The comparison between the charge density of LSDA (not considering U ) and that of LSDA+ U (considering U ) demonstrates that the trend of ionic crystal for NiO is obvious.

다중강전자 상태를 가진 육방정계물질의 전자구조 계산

다중강전자 상태의 <TEX>$YMnO_3,\;ScMnO_3$</TEX>의 전자구조와 자기구조를 국소스핀밀도근사(LSDA)를 이용하여 계산하였다. 강자성 상태이며 강유전 상태의 전자구조는 육방정계 구조로 인하여 Mn 3d 에너지띠가 분리되어 띠틈을 나타내었다. 이러한 에너지 띠틈과 작은 Y, Sc 이온의 반경으로 인하여 <TEX>$YMnO_3,\;ScMnO_3$</TEX>는 반강자성 강유전적 성질을 가지는 다중강전자 구조를 가지고 있음을 보았다. 또한 총에너지 계산을 통하여 반강자성, 강유전 상태가 가장 안정됨이 실험과 일치하였다. We have studied electronic structures and magnetic properties of <TEX>$YMnO_3,\;ScManO_3$</TEX> with hexagonal structure using Full Potential Linearized Augmented Plane Wave (FLAPW) method based on LSDA method. LSDA calculation results show that multiferroic <TEX>$YMnO_3$</TEX> shows energy gap due to hexagonal symmetry and magnetic interaction. Because of insulating gap and small Y ion, <TEX>$YMnO_3$</TEX> shows magnetic and ferroelectric state. However, <TEX>$ScMnO_3$</TEX> does not show the energy gap because of strong hybridization of Mn-O for LSDA calculation. We confirmed the stability of multiferroic state for <TEX>$YMnO_3\;and\;ScManO_3$</TEX> using total energy calculations. The antiferromagnetic and ferroelectric states have the lowest energy about 100 meV.

Magnetic and optical properties of Fe2VAl and Fe3Al

Abstract Full-potential linearized augmented plane wave plus local orbital method (FPLAPW + lo) calculations were performed for Fe2VAl and Fe3Al in order to investigate magnetic and optical properties and to show the origin of various optical transitions. It was found that the lattice constant and spin magnetic moments with the GGA method differ more from the respective experimental values than those calculated with the LSDA method. Furthermore, our calculated lattice constant and spin magnetic moments with the LSDA method were in overall better agreement with experiment. Our predictions agreed well with recent experimental reflectivity spectra. Meanwhile, the spectral peaks at the transitions were analyzed from the imaginary part of the dielectric function.

Predicting Hydration Free Energies of Neutral Compounds by a Parametrization of the Polarizable Continuum Model

A parametrization of the polarizable continuum model (PCM) is presented having the experimental hydration free energies of 215 neutral molecules as target. The cavitation and dispersion contributions were based on the Tuñon-Silla-Pascual-Ahuir (Tuñon; et al. Chem. Phys. Lett. 1993, 203, 289) and Floris-Tomasi (Floris, F.; Tomasi, J. J. Comput. Chem. 1989, 10, 616) expressions, respectively. Both the polar and nonpolar contributions were evaluated on the same solvent-excluding molecular surface that used unscaled Bondi atomic radii. The parametrization was provided for the HF, Xalpha, LSDA, B3LYP, and mPW1PW91 methods at the 6-31G(d) basis set, and the results are in fair agreement with the experimental data. For the sake of comparison, the PCM(UAHF) and our parametrization (PCM2), both at HF level, have produced DeltaG(PCM(UAHF)) = aDeltaGexp (a = 1.02 +/- 0.02, r = 0.945, sd = 0.987, Ftest = 1778) and DeltaG(PCM2) = aDeltaGexp (a = 0.95 +/- 0.02, r = 0.952, sd = 0.843, Ftest = 2070), respectively. The mean absolute deviations from experimental data were 0.67 and 0.68 kcal/mol for PCM(UAHF) and PCM2, respectively.

Electron Affinities, Ionization Energies, and Fragmentation Energies of Fen Clusters (n = 2−6): A Density Functional Theory Study

The electronic and geometrical structures of the ground and exited states of Fen, Fen-, and Fen+ are computed by density functional theory. Because the assignment of the ground states of Fe3, Fe3-, Fe4, and Fe4- is controversial, these systems are studied using several different functionals. It appears that the LSDA and B3LYP methods do not work well for iron clusters and should be avoided. The number of unpaired electrons in the neutral ground states is 6(Fe2), 10(Fe3), 14(Fe4), 16(Fe5), and 20(Fe6). The number of unpaired electrons in the ground states of the anions and cations differ by one from the corresponding neutral, except for Fe4+, which has three fewer unpaired electrons than Fe4. The computed DFT adiabatic electron affinities and ionization potentials of the neutral clusters are in good agreement with experiment. Fragmentation energies are in qualitative agreement with experiment, where the error is about 1 eV for the dissociation energy of the iron dimer. The natural bond analysis allows one ...