This study employs ab initio calculations based on density functional theory (DFT) to investigate the structural properties,
H-NMR spectra, and vibrational spectra of methane sulfonic acid (MSA) at ...low degree of hydration. The findings reveal that energetically stable structures are formed by small clusters consisting of one or two MSA molecules (m = 1 and 2) and one or two water molecules in (MSA)
·(H
O)
(m = 1-2 and n = 1-5).These stable structures arise from the formation of strong cyclic hydrogen bonds between the proton of the hydroxyl (OH) group in MSA and the water molecules. However, clusters containing three or more water molecules (n > 2) exhibit proton transfer from MSA to water, resulting in the formation of ion-pairs composed of CH
SO
and H
O
species. The measured
H-NMR spectra demonstrate the presence of hydrogen-bonded interactions between MSA and water, with a single MSA molecule interacting with water molecules. This interaction model accurately represents the hydrogen bonding network, as supported by the agreement between the experimental and calculated NMR chemical shift results.
► We have studied the structural, elastic, electronic and phonon properties of Co2MnX (X=Si, Ge, Al, Ga). ► Elastically, all the compounds have been found to be stable. ► The electronic structure ...calculations were performed using pseudopotentials. ► Obtained the phonon frequencies and the phonon densities of states.
First-principles self-consistent pseudopotential plane wave calculations based on density functional theory were performed in order to study magnetic moments, density of states and half-metallicity of L21 type full Heusler alloys with formula Co2MnX (X=Si, Ge, Al, Ga). Half-metallicity in terms of total spin-moments was discussed since perfect half-metals show Slater–Pauling (SP) behavior. The effects of the atomic number on the lattice constants, the bulk moduli and the Curie temperatures were shown. The magnetic moments were calculated, while slight deviations of about 0.06–0.16μB were found for Co2MnAl and Co2MnGa, the Co2MnSi and Co2MnGe have been found to be half metals. Mechanical stability of these compounds has been analyzed in terms of their elastic constants. The size of the gap in the minority states and the position of EF inside the gap was also discussed as it is an important factor for the application of half-metallic ferromagnetic alloys. Finally, phonon dispersion curves and the density of states were calculated by employing the density-functional perturbation theory and discussed.
Abstract
The mechanical and thermodynamic properties of polyanionic hydrides XAlSiH (X = Sr, Ca, and Ba) were evaluated using density functional theory (DFT). The thermal parameters of XAlSiH ...hydrides, such as the Grüneisen parameter
γ
, heat capacity, and thermal expansion coefficient, were computed for the first time. The quasi-harmonic Debye model was used to determine these parameters over a range of pressures (0–40 GPa) and temperatures (0–1000 K). The gravimetric hydrogen storage capacities for BaAlSiH, SrAlSiH, and CaAlSiH were found to be 0.52%, 0.71%, and 1.05%, respectively. The hydrogen desorption temperatures for these compounds were also simulated at 748.90 K, 311.57 K, and 685.40 K. Furthermore, semiconducting behavior with an indirect bandgap value between 0.2 and 0.7 eV was exhibited by these compounds using the GGA and LDA approximation, and between 0.7 and 1.2 eV using the mBJ-GGA and mBJ-LDA approximation. Accurate elastic constants for single crystals were obtained from the calculated stress–strain relationships. The elastic constants for the XAlSiH compounds were significantly higher than those for other hydrides. The 001 direction was more compressible than the 100 direction in the hexagonal structure of XAlSiH. A lower bulk modulus than metallic hydrides was exhibited by these materials, indicating that XAlSiH compounds (X = Sr, Ca, and Ba) were highly compressible. The melting temperature for CaAlSiH was higher than that for SrAlSiH and BaAlSiH. Consequently, the decomposition temperature for XAlSiH (X = Sr and Ba) at which hydrogen was released from a fuel cell was lower than that for CaAlSiH. The bonding behavior of CaAlSiH was more directional than that of SrAlSiH and BaAlSiH. Brittle materials were XAlSiH (X = Sr, Ca, and Ba). Our PBE calculations yield linear compressibility and orientation-dependent Young’s modulus. Materials composed of hexagonal XAlSiH (where X represents Sr, Ca, or Ba elements) exhibit anisotropy in Young’s modulus but isotropy in bulk modulus.
Our calculations allowing to establish a link between atomic topology and properties, based on the interpretation of the electronic structure. ScXCo
2
Sb
2
(
X
= V, Nb and Ta) double half-Heusler ...alloys (DHH) are nonmagnetic materials. Based on an ab initio study these materials is found to be semiconductors with an indirect band gap in the range 0.56–0.81 eV. Our DFT calculations confirm that the band gap increasing upon the replacement of V by Nb by Ta atoms. In all compounds Co-d orbitals are locating close to the Fermi level and a hybridization of Co-d, X-d and Sc-d bands lies above the Fermi level. More precisely, the optical properties have been calculated and discussed. The photon energy dependence of the dielectric function and optical conductivity is determined from 0 up to 20 eV. Prominent absorptions are observed in these compounds in the energy region of 2–4.0 eV due to interband optical transitions. The reflectivity spectra and the refraction index are also calculated and discussed. The structural stability of ScXCo
2
Sb
2
(
X
= V, Nb and Ta) DHH has been confirmed by elastic constants calculations. The atomic bonds between nearest neighbors along (100) planes are weaker than those along (001) planes. However, for ScVCo
2
Sb
2
, the atomic bonds are weaker along (001). The studied materials are found to be somewhat hard compounds, elastically stable and have a brittle character except ScVCo
2
Sb
2
compound. The positive frequencies in the phonon dispersions of ScXCo
2
Sb
2
(
X
= V, Nb, Ta) DHH, indicating that they are dynamically stable.
•The total magnetic moment of all investigated compounds is obtained to be 2 µB.•The mechanical stability test performed on the computed elastic constants Cij demonstrate that investigated compounds ...are mechanically stable.•The GGA (GGA+U) and mBJ-GGA (mBJ-GGA+U) approximations are used for the calculation of electronic properties in the most stable phase B1.•These materials could be useful for spintronic application.
We report ab-initio calculation of the structural, magnetic, elastic, and electronic properties of the PrX (X = P, As and Bi). The structural stability and phase transition of PrX (X = P, As, Bi) compounds in (NaCl-type), (CsCl-type), (Zinc blende-type), WC-Bh (Hexagonal) and L10 (Tetragonal) structures in ferromagnetic state are investigated using the augmented plane wave plus local orbital (APW + lo) method within GGA + U, and mBJ-GGA + U approximations. Careful inspection of electronic properties indicates that most of the compounds exhibit half-metallic behavior. The total magnetic moment of all investigated compounds is obtained to be 2 µB. The mechanical stability test performed on the computed elastic constants Cij demonstrate that investigated compounds are mechanically stable. To elucidate chemical stability, chemical bonds are investigated and found to be mainly characterized by an ionic-covalent mixture. Moreover, elastic anisotropy of all compounds is calculated. Subsequently.
We report ab initio investigation of structural, electronic, magnetic and optical properties of the NiFe2O4 compound. Hubbard parameters are computed for both Ni and Fe atoms. Employing generalized ...gradient approximation (GGA) and GGA + U approximations and taking into consideration four possible types of atomic arrangements, we identify the most stable structural-magnetic configuration of the system. Interestingly, the inverse spinel NiFe2O4 compound is found to exhibit a ferrimagnetic structure. The ground state structural lattice parameters and the interatomic distances of spinel NiFe2O4 compound are computed. Furthermore, band structure calculations demonstrate that NiFe2O4 compound exhibits large band gaps in both spin configurations with a large magnetic moment. Energetically, ferrite nickel favors the inverse spinel phase in which Fe and Ni cations in either octahedral or tetrahedral sites adopt the high-spin configuration. We found that the energy of the normal spinel is higher than that of the inverse spinel, confirming that inverse spinel is the most stable structure of the NiFe2O4 compound. The optical behavior of the NiFe2O4 compound is characterized by calculating the real and imaginary part of the dielectric function, the absorption coefficients, the refractive index, the optical conductivity and the energy loss. Optimizing structural, electronic, magnetic and optical properties of this novel compound is crucial for exploring and utilizing it for modern device applications.
Analyses based on first-principles simulations have revealed new details about the mechanical and thermodynamic characteristics of NaBH4 and NaAlH4 complex hydrides in α, β and γ phases. Using the ...quasi-harmonic Debye model, thermal parameters like the Debye temperature, the heat capacity, and the thermal expansion coefficient of NaXH4 (X = B, Al) complex hydrides are calculated in α, β and γ phases at different pressures and temperatures for the first time. Single-crystal elastic constants may be derived from the stress-strain relationship calculations. Although NaBH4 has a stronger compressibility modulus than NaAlH4, the distance dB-H is shorter than dAl-H, which may be explained by the presence of the covalent bond in BH4 and AlH4 in NaXH4 (X = B, Al). The melting points of NaXH4 (X = B, Al) may be used to estimate the decomposition temperatures of hydrogen. β-NaBH4 has a higher melting point than α-NaAlH4. Thus, the decomposition temperature of NaAlH4 at which hydrogen is released from a fuel cell is expected to be lower than that of NaBH4. β-NaBH4 has a more directed bonding tendency than α-NaAlH4 does. Except for the phase γ-NaAlH4, the NaXH4 (X = B, Al) compounds are ductile. NaBH4 deforms more than NaAlH4 in uniaxial deformation, yet both are centrally strong solids. Our PBE calculations result in the linear compressibility and orientation-dependent Young's modulus. Tetragonal β-NaBH4 and α-NaAlH4 structures have an isotropic bulk modulus but an anisotropic Young's modulus.
•Although NaBH4 has a stronger compressibility modulus than NaAlH4.•The mechanical stability demonstrate that investigated compounds are mechanically stable.•Tetragonal β-NaBH4 and α-NaAlH4 structures have an isotropic bulk modulus but an anisotropic Young's modulus.•These materials could be useful for storage of hydrogen application.
The inverse Heusler alloys such as Ti
2
CoSi, Mn
2
CoAl and Cr
2
ZnSi were studied in the framework of density functional theory using FP-LAPW linearised augmented plane wave method in order to ...determine the different physical properties such as structural, electronic, magnetic and thermoelectric. The generalised gradient approximation (GGA) was used to treat the exchange-correlation energy and the Beck-Johnson (mBJ) approach was used to calculate the electronic properties. In all studied compounds, the stable type Hg
2
CuTi was energetically more favourable than Cu
2
MnAl type structure. The results show that two compounds (Ti
2
CoSi and Mn
2
CoAl) are both ferromagnetic (FM) while Cr
2
ZnSi is antiferromagnetic (AFM). The compounds Ti
2
CoSi and Mn
2
CoAl have a total magnetic moment of 3 and 2 μ
B,
respectively, whereas the Cr
2
ZnSi alloy has a total magnetic moment equals zero. The Ti
2
CoSi, Mn
2
CoAl and Cr
2
ZnSi compounds exhibit half-metallic (HM) character with 100% spin polarisation at the Fermi level. Finally, the semi-classical Boltzmann theory implicit in the BoltzTraP code was used to calculate the electronic transport coefficients such as thermal and electrical conductivity, the Seebeck coefficient and the factor of merit.
