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19 pages, 4611 KiB

Open AccessArticle

Assessing the Novel Mixed Tutton Salts K₂Mn_0.03Ni_0.97(SO₄)₂(H₂O)₆ and K₂Mn_0.18Cu_0.82(SO₄)₂(H₂O)₆ for Thermochemical Heat Storage Applications: An Experimental–Theoretical Study

by João G. de Oliveira Neto, Jailton R. Viana, Antonio D. da S. G. Lima, Jardel B. O. Lopes, Alejandro P. Ayala, Mateus R. Lage, Stanislav R. Stoyanov, Adenilson O. dos Santos and Rossano Lang

Molecules 2023, 28(24), 8058; https://doi.org/10.3390/molecules28248058 - 13 Dec 2023

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Abstract

In this paper, novel mixed Tutton salts with the chemical formulas K₂Mn_0.03Ni_0.97(SO₄)₂(H₂O)₆ and K₂Mn_0.18Cu_0.82(SO₄)₂(H₂O)₆ were synthesized and [...] Read more.

In this paper, novel mixed Tutton salts with the chemical formulas K₂Mn_0.03Ni_0.97(SO₄)₂(H₂O)₆ and K₂Mn_0.18Cu_0.82(SO₄)₂(H₂O)₆ were synthesized and studied as compounds for thermochemical heat storage potential. The crystallographic structures of single crystals were determined by X-ray diffraction. Additionally, a comprehensive computational study, based on density functional theory (DFT) calculations and Hirshfeld surface analysis, was performed to calculate structural, electronic, and thermodynamic properties of the coordination complexes [M^II(H₂O)₆]²⁺ (M^II = Mn, Ni, and Cu), as well as to investigate intermolecular interactions and voids in the framework. The axial compressions relative to octahedral coordination geometry observed in the crystal structures were correlated and elucidated using DFT investigations regarding Jahn–Teller effects arising from complexes with different spin multiplicities. The spatial distributions of the frontier molecular orbital and spin densities, as well as energy gaps, provided further insights into the stability of these complexes. Thermogravimetry, differential thermal analysis, and differential scanning calorimetry techniques were also applied to identify the thermal stability and physicochemical properties of the mixed crystals. Values of dehydration enthalpy and storage energy density per volume were also estimated. The two mixed sulfate hydrates reported here have low dehydration temperatures and high energy densities. Both have promising thermal properties for residential heat storage systems, superior to the Tutton salts previously reported. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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19 pages, 8138 KiB

Open AccessArticle

Exploring the Relationship between the Structural Characteristics and Mechanical Behavior of Multicomponent Fe-Containing Phases: Experimental Studies and First-Principles Calculations

by Dongtao Wang, Xiaozu Zhang, Hiromi Nagaumi, Minghe Zhang, Pengfei Zhou, Rui Wang and Bo Zhang

Molecules 2023, 28(20), 7141; https://doi.org/10.3390/molecules28207141 - 17 Oct 2023

Cited by 1 | Viewed by 933

Abstract

A comprehensive understanding of the structural characteristics and mechanical behavior of Fe-containing phases is important for high-Fe-level Al-Si alloys. In this paper, the crystal characteristics, thermal stability, thermophysical properties and mechanical behavior of multicomponent α-AlFeMnSi and α-AlFeMnCrSi phases are investigated by experimental studies [...] Read more.

A comprehensive understanding of the structural characteristics and mechanical behavior of Fe-containing phases is important for high-Fe-level Al-Si alloys. In this paper, the crystal characteristics, thermal stability, thermophysical properties and mechanical behavior of multicomponent α-AlFeMnSi and α-AlFeMnCrSi phases are investigated by experimental studies and first-principles calculations. The results indicate that it is easier for Fe and Cr to substitute the Mn-12j site in α-AlMnSi in thermodynamics; Cr is preferred to Fe for substituting Mn-12j/k sites due to its lower formation enthalpy after single substitutions at Mn atom sites. The α-AlFeMnCrSi phase shows higher thermal stability, modulus and intrinsic hardness and a lower volumetric thermal expansion coefficient at different temperatures due to the strong chemical bonding of Si-Fe and Si-Cr. Moreover, the α-AlFeMnCrSi phase has a higher ideal strength (10.65 GPa) and lower stacking fault energy (1.10 × 10³ mJ/m²). The stacking fault energy evolution of the different Fe-containing phases is mainly attributed to the differential charge-density redistribution. The strong chemical bonds of Si-Fe, Si-Mn and Si-Cr are important factors affecting the thermophysical and mechanical behaviors of the α-AlFeMnCrSi phase. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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15 pages, 3497 KiB

Open AccessArticle

Density Functional Theory Study of the Point Defects on KDP (100) and (101) Surfaces

by Xiaoji Zhao, Yanlu Li and Xian Zhao

Molecules 2022, 27(24), 9014; https://doi.org/10.3390/molecules27249014 - 17 Dec 2022

Cited by 2 | Viewed by 1414

Abstract

Surface defects are usually associated with the formation of other forms of expansion defects in crystals, which have an impact on the crystals’ growth quality and optical properties. Thereby, the structure, stability, and electronic structure of the hydrogen and oxygen vacancy defects (V [...] Read more.

Surface defects are usually associated with the formation of other forms of expansion defects in crystals, which have an impact on the crystals’ growth quality and optical properties. Thereby, the structure, stability, and electronic structure of the hydrogen and oxygen vacancy defects (V_H and V_O) on the (100) and (101) growth surfaces of KDP crystals were studied by using density functional theory. The effects of acidic and alkaline environments on the structure and properties of surface defects were also discussed. It has been found that the considered vacancy defects have different properties on the (100) and (101) surfaces, especially those that have been reported in the bulk KDP crystals. The (100) surface has a strong tolerance for surface V_H and V_O defects, while the V_O defect causes a large lattice relaxation on the (101) surface and introduces a deep defect level in the band gap, which damages the optical properties of KDP crystals. In addition, the results show that the acidic environment is conducive to the repair of the V_H defects on the surface and can eliminate the defect states introduced by the surface V_O defects, which is conducive to improving the quality of the crystal surface and reducing the defect density. Our study opens up a new way to understand the structure and properties of surface defects in KDP crystals, which are different from the bulk phase, and also provides a theoretical basis for experimentally regulating the surface defects in KDP crystals through an acidic environment. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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14 pages, 3636 KiB

Open AccessArticle

Regulating the Electronic Structure of Freestanding Graphene on SiC by Ge/Sn Intercalation: A Theoretical Study

by Xingyun Luo, Guojun Liang, Yanlu Li, Fapeng Yu and Xian Zhao

Molecules 2022, 27(24), 9004; https://doi.org/10.3390/molecules27249004 - 17 Dec 2022

Cited by 2 | Viewed by 1449

Abstract

The intrinsic n-type of epitaxial graphene on SiC substrate limits its applications in microelectronic devices, and it is thus vital to modulate and achieve p-type and charge-neutral graphene. The main groups of metal intercalations, such as Ge and Sn, are found to be [...] Read more.

The intrinsic n-type of epitaxial graphene on SiC substrate limits its applications in microelectronic devices, and it is thus vital to modulate and achieve p-type and charge-neutral graphene. The main groups of metal intercalations, such as Ge and Sn, are found to be excellent candidates to achieve this goal based on the first-principle calculation results. They can modulate the conduction type of graphene via intercalation coverages and bring out interesting magnetic properties to the entire intercalation structures without inducing magnetism to graphene, which is superior to the transition metal intercalations, such as Fe and Mn. It is found that the Ge intercalation leads to ambipolar doping of graphene, and the p-type graphene can only be obtained when forming the Ge adatom between Ge layer and graphene. Charge-neutral graphene can be achieved under high Sn intercalation coverage (7/8 bilayer) owing to the significantly increased distance between graphene and deformed Sn intercalation. These findings would open up an avenue for developing novel graphene-based spintronic and electric devices on SiC substrate. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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17 pages, 2222 KiB

Open AccessArticle

Fast Quantum Approach for Evaluating the Energy of Non-Covalent Interactions in Molecular Crystals: The Case Study of Intermolecular H-Bonds in Crystalline Peroxosolvates

by Alexander G. Medvedev, Andrei V. Churakov, Mger A. Navasardyan, Petr V. Prikhodchenko, Ovadia Lev and Mikhail V. Vener

Molecules 2022, 27(13), 4082; https://doi.org/10.3390/molecules27134082 - 24 Jun 2022

Cited by 10 | Viewed by 2079

Abstract

Energy/enthalpy of intermolecular hydrogen bonds (H-bonds) in crystals have been calculated in many papers. Most of the theoretical works used non-periodic models. Their applicability for describing intermolecular H-bonds in solids is not obvious since the crystal environment can strongly change H-bond geometry and [...] Read more.

Energy/enthalpy of intermolecular hydrogen bonds (H-bonds) in crystals have been calculated in many papers. Most of the theoretical works used non-periodic models. Their applicability for describing intermolecular H-bonds in solids is not obvious since the crystal environment can strongly change H-bond geometry and energy in comparison with non-periodic models. Periodic DFT computations provide a reasonable description of a number of relevant properties of molecular crystals. However, these methods are quite cumbersome and time-consuming compared to non-periodic calculations. Here, we present a fast quantum approach for estimating the energy/enthalpy of intermolecular H-bonds in crystals. It has been tested on a family of crystalline peroxosolvates in which the H∙∙∙O bond set fills evenly (i.e., without significant gaps) the range of H∙∙∙O distances from ~1.5 to ~2.1 Å typical for strong, moderate, and weak H-bonds. Four of these two-component crystals (peroxosolvates of macrocyclic ethers and creatine) were obtained and structurally characterized for the first time. A critical comparison of the approaches for estimating the energy of intermolecular H-bonds in organic crystals is carried out, and various sources of errors are clarified. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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8 pages, 935 KiB

Open AccessArticle

Effect of Strain on the Electronic Structure and Phonon Stability of SrBaSn Half Heusler Alloy

by Shakeel Ahmad Khandy, Ishtihadah Islam, Kulwinder Kaur, Atif Mossad Ali and Alaa F. Abd El-Rehim

Molecules 2022, 27(12), 3785; https://doi.org/10.3390/molecules27123785 - 12 Jun 2022

Cited by 3 | Viewed by 1604

Abstract

This paper presents the strain effects on the structural, electronic and phonon properties of a newly proposed SrBaSn half Heusler compound. Since it is stable considering chemical thermodynamics, we tested its strength against uniform strain w.r.t phonon spectrum and it produces a direct [...] Read more.

This paper presents the strain effects on the structural, electronic and phonon properties of a newly proposed SrBaSn half Heusler compound. Since it is stable considering chemical thermodynamics, we tested its strength against uniform strain w.r.t phonon spectrum and it produces a direct bandgap of 0.7 eV. The direct bandgap reduces to 0.19 eV at −12% strain beyond which the structure is unstable. However, an indirect gap of 0.63 eV to 0.39 eV is observed in the range of +5% to +8% strain and afterwards the strain application destabilizes the structure. From elastic parameters, the ductile nature of this material is observed. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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15 pages, 4349 KiB

Open AccessArticle

Density Functional Theory Approach to the Vibrational Properties and Magnetic Specific Heat of the Covalent Chain Antiferromagnet KFeS₂

by Airat Kiiamov, Maxim Kuznetsov, Dorina Croitori, Irina Filippova, Vladimir Tsurkan, Hans-Albrecht Krug von Nidda, Zakir Seidov, Franz Mayr, Sebastian Widmann, Farit Vagizov, Dmitrii Tayurskii and Lenar Tagirov

Molecules 2022, 27(9), 2663; https://doi.org/10.3390/molecules27092663 - 20 Apr 2022

Cited by 2 | Viewed by 1927

Abstract

Ternary potassium-iron sulfide, KFeS₂, belongs to the family of highly anisotropic quasi-one-dimensional antiferromagnets with unusual “anti-Curie–Weiss” susceptibility, quasi-linearly growing with a rising temperature up to 700 K, an almost vanishing magnetic contribution to the specific heat, drastically reduced magnetic moment, [...] Read more.

Ternary potassium-iron sulfide, KFeS₂, belongs to the family of highly anisotropic quasi-one-dimensional antiferromagnets with unusual “anti-Curie–Weiss” susceptibility, quasi-linearly growing with a rising temperature up to 700 K, an almost vanishing magnetic contribution to the specific heat, drastically reduced magnetic moment, etc. While some of the measurements can be satisfactorily described, the deficiency of the entropy changes upon the magnetic transition and the spin state of the iron ion remains a challenge for the further understanding of magnetism. In this work, high-quality single-crystalline samples of KFeS₂ were grown by the Bridgman method, and their stoichiometry, crystal structure, and absence of alien magnetic phases were checked, utilizing wave-length dispersive X-ray electron-probe microanalysis, powder X-ray diffraction, and ⁵⁷Fe Mössbauer spectroscopy, respectively. An ab initio approach was developed to calculate the thermodynamic properties of KFeS₂. The element-specific phonon modes and their density of states (PDOS) were calculated applying the density functional theory in the DFT + U version, which explicitly takes into account the on-site Coulomb repulsion U of electrons and their exchange interaction J. The necessary calibration of the frequency scale was carried out by comparison with the experimental iron PDOS derived from the inelastic nuclear scattering experiment. The infrared absorption measurements confirmed the presence of two high-frequency peaks consistent with the calculated PDOS. The calibrated PDOS allowed the calculation of the lattice contribution to the specific heat of KFeS₂ by direct summation over the phonon modes without approximations and adjustable parameters. The temperature-dependent magnetic specific heat evaluated by subtraction of the calculated phonon contribution from the experimental specific heat provides a lower boundary for estimating the reduced spin state of the iron ion. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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14 pages, 10332 KiB

Open AccessArticle

Remarkable Nonlinear Properties of a Novel Quinolidone Derivative: Joint Synthesis and Molecular Modeling

by Clodoaldo Valverde, Rafael S. Vinhal, Luiz F. N. Naves, Jean M. F. Custódio, Basílio Baseia, Heibbe Cristhian B. de Oliveira, Caridad N. Perez, Hamilton B. Napolitano and Francisco A. P. Osório

Molecules 2022, 27(8), 2379; https://doi.org/10.3390/molecules27082379 - 07 Apr 2022

Cited by 4 | Viewed by 1555

Abstract

A novel 4(1H) quinolinone derivative (QBCP) was synthesized and characterized with single crystal X-ray diffraction. Hirshfeld surfaces (HS) analyses were employed as a complementary tool to evaluate the crystal intermolecular interactions. The molecular global reactivity parameters of QBCP were studied using HOMO and [...] Read more.

A novel 4(1H) quinolinone derivative (QBCP) was synthesized and characterized with single crystal X-ray diffraction. Hirshfeld surfaces (HS) analyses were employed as a complementary tool to evaluate the crystal intermolecular interactions. The molecular global reactivity parameters of QBCP were studied using HOMO and LUMO energies. In addition, the molecular electrostatic potential (MEP) and the UV-Vis absorption and emission spectra were obtained and analyzed. The supermolecule (SM) approach was employed to build a bulk with 474,552 atoms to simulate the crystalline environment polarization effect on the asymmetric unit of the compound. The nonlinear optical properties were investigated using the density functional method (DFT/CAM-B3LYP) with the Pople’s 6-311++G(d,p) basis set. The quantum DFT results of the linear polarizability, the average second-order hyperpolarizability and the third-order nonlinear susceptibility values were computed and analyzed. The results showed that the organic compound (QBCP) has great potential for application as a third-order nonlinear optical material. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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22 pages, 6938 KiB

Open AccessArticle

Crystal Structure, Topology, DFT and Hirshfeld Surface Analysis of a Novel Charge Transfer Complex (L3) of Anthraquinone and 4-{[(anthracen-9-yl)meth-yl] amino}-benzoic Acid (L2) Exhibiting Photocatalytic Properties: An Experimental and Theoretical Approach

by Adeeba Ahmed, Aysha Fatima, Sonam Shakya, Qazi Inamur Rahman, Musheer Ahmad, Saleem Javed, Huda Salem AlSalem and Aiman Ahmad

Molecules 2022, 27(5), 1724; https://doi.org/10.3390/molecules27051724 - 06 Mar 2022

Cited by 24 | Viewed by 2504

Abstract

Here, we report a facile route to the synthesizing of a new donor–acceptor complex, L3, using 4-{[(anthracen-9-yl)meth-yl] amino}-benzoic acid, L2, as donor moiety with anthraquinone as an acceptor moiety. The formation of donor–acceptor complex L3 was facilitated via H-bonding and characterized by single-crystal [...] Read more.

Here, we report a facile route to the synthesizing of a new donor–acceptor complex, L3, using 4-{[(anthracen-9-yl)meth-yl] amino}-benzoic acid, L2, as donor moiety with anthraquinone as an acceptor moiety. The formation of donor–acceptor complex L3 was facilitated via H-bonding and characterized by single-crystal X-ray diffraction. The X-ray diffraction results confirmed the synthesized donor–acceptor complex L3 crystal belongs to the triclinic system possessing the P-1 space group. The complex L3 was also characterized by other spectral techniques, viz., FTIR and UV absorption spectroscopy, which confirmed the formation of new bonds between donor L2 moiety and acceptor anthraquinone molecule. The crystallinity and thermal stability of the newly synthesized complex L3 was confirmed by powdered XRD and TGA analysis and theoretical studies; Hirshfeld surface analysis was performed to define the type of interactions occurring in the complex L3. Interestingly, theoretical results were successfully corroborated with experimental results of FTIR and UV absorption. The density functional theory (DFT) calculations were employed for HOMO to LUMO; the energy gap (∆E) was calculated to be 3.6463 eV. The complex L3 was employed as a photocatalyst for the degradation of MB dye and was found to be quite efficient. The results showed MB dye degraded about 90% in 200 min and followed the pseudo-first-order kinetic with rate constant k = 0.0111 min⁻¹ and R² = 0.9596. Additionally, molecular docking reveals that the lowest binding energy was −10.8 Kcal/mol which indicates that the L3 complex may be further studied for its biological applications. Full article

(This article belongs to the Special Issue Applications of Density Functional Theory in Crystalline Materials)

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