Enthalpies Of Formation Research Articles

Study of Raman Scattering of Light in Liquid Arenes and Their Halogen-Substituted ones in the Low-Frequency Region of the Spectrum

Purpose. Investigation of Raman scattering of light in liquid arenas and their halogenated ones in the low-frequency range of the spectrum, taking into account the clustering processes in their structure.Methods. Raman spectroscopy methods were used, as well as a modeling method using cluster representations of the structure of liquids. Raman spectra of light in the low-frequency range from 17 to 500 cm–1 were obtained using a LabRAM HR Evolution spectrometer at room temperature (23°C).Results. The analysis of theoretical and experimental work on the properties of dimeric configurations of benzene and on the effect of clustering processes in substances on their IR and Raman spectra is carried out. Low-frequency Raman spectra of liquid benzene, o-xylene, ethylbenzene, fluorobenzene, chlorobenzene, brombenzene, toluene, o-fluorotoluene, m-fluorotoluene, p-fluorotoluene, o-chlorotoluene, m-chlorotoluene, p-chlorotoluene, 2,4-dichlorotoluene, 2,6-dichlorotoluene were obtained. The model of formation and disintegration of cluster formations has been tested. Formulas have been obtained for estimating the minimum frequency of libration oscillations of the ωmin dimer formation in the cluster structure and the position of the maxima of spectral bands in the low-frequency region of the Raman spectrum, depending on the number of particles included in the cluster formations. The theoretical results obtained by ωmin are in satisfactory agreement with the experimental data within the total error.The proposed model makes it possible to predict the position of some spectral bands of the Raman spectrum. The presence of other spectral bands is obviously related to the multiparticle interaction in the cluster structure and requires additional research.Conclusion. The proposed model of formation and decay of cluster formations and the relations following from it allow us to estimate the value of the minimum frequency in the low-frequency range of the Raman spectrum of liquid arenes and their halogenated ones from the known values of the enthalpy of formation and the moment of inertia of the dimer. Conversely, using known values of the minimum frequency, the values of the enthalpy of formation and the moment of inertia of the dimer can be estimated without resorting to complex quantum mechanical calculations.

Pressure‐Induced Effects on BaPbO3: A Prospectively Valuable Material for Piezoelectric Applications via DFT

AbstractEmploying density functional theory within the Wien2k code, first‐principle calculations are conducted to explore the impact of applied pressure up to 80 GPa on the structural, mechanical, thermal, and electronic characteristics of BaPbO3. Demonstrating metallic behavior with ductile attributes, BaPbO3 exhibits a decreasing anisotropic nature under escalating pressure. Evaluation of cubic elastic constants, optimization curves, and enthalpy of formation indicates the compound's mechanical and thermodynamic stability under high pressure conditions. Calculated values of C11 and C44 reflect heightened resistance to unidirectional compression and increased stiffness under pressure. These mechanical properties position BaPbO3 as a promising candidate for diverse industrial applications across varying pressure ranges, including utilization in piezoelectric materials (0–20 GPa) and high‐pressure sensors. Additionally, charge density contours suggest a combination of ionic (Ba─Pb) and covalent bonding (Pb─O) within the compound's constituent atoms. The material can exhibit potential applications as a piezoelectric sensor at 0–20 GPa, high‐pressure actuators ≈20 GPa, and as a high melting temperature resistive substrate for laser welding and cutting materials.

Quantum Chemistry and Pharmacy: Diagnostic Check of the Thermochemistry of Ibuprofen.

The thermodynamic data on ibuprofen available in the literature shows that the disarray of experimental results is unacceptable for this very important drug. The data on ibuprofens available in the literature were collected, combined with our complementary experimental results and evaluated. The enthalpies of combustion and formation of the crystalline RS-(±)- and S-(+)-ibuprofens were measured using high-precision combustion calorimetry. The temperature dependence of the vapour pressure of S-(+)-ibuprofen was measured using the transpiration method and the enthalpy of vaporization was derived from this measurement. The enthalpies of fusion of both compounds were measured using DSC. The G4 calculations have been carried out to determine the enthalpy of formation in the gaseous state of the most stable conformer. Thermochemical properties of the compounds studied were evaluated and tested for consistency with the "centerpiece approach". A set of reliable and consistent values of thermodynamic properties of ibuprofens at 298.15 K is recommended for thermochemical calculations of the pharmaceutical processes. The diagnostic protocol was developed to distinguish between the "sick" or "healthy" thermodynamic data. This diagnostic is also applicable to other drugs with a different structure than ibuprofen.

Ordered phases in ternary wurtzite group-III nitrides: A first-principles study

A first-principles-based lattice model is applied to investigate the ordered phases of mixed group-III nitride ternary alloys. The model surveys the atomistic configurations with the lowest formation enthalpy for a wide range of compositions. We found novel ordered phases in wurtzite structures having specific compositions of three- and four-sevenths molar fractions of group-III cations. The configurations of group–III atoms on cation sites in those phases consist of a characteristic fragment of the ordered phases of one-third and one-half ordered phases that were previously reported. The simulation results indicate that group-III cations in ternary nitrides follow spatial positioning “atomistic distancing rules” that can be described by the pairwise interaction energy of group-III cations to realize the stabilities of the ordered structures. To minimize the formation enthalpy of a mixed crystal, the minor B, Al, Ga, and In atoms on cation sites remain neither too close to nor too distant from each other, allowing those ordered phases to be realized.

Thermodynamic assessment of the Cr–Si binary system

A thermodynamic evaluation of the Cr–Si system was performed concerning the latest experimental phase diagram and with the aid of first-principles calculations. The thermodynamic parameters for the Gibbs energy of pure Cr were modified based on the new experimental value of 1861 °C for the melting point of pure Cr, which was previously reported as 1907 °C in the SGTE database. The Gibbs energy descriptions of the Cr3Si and Cr5Si3 phases were revised using Cr3(Cr,Si)- and (Cr,Si)5Si3-type two-sublattice models to reproduce the latest experimental results of their solubility composition ranges, that is, Cr3Si extending toward the Cr-rich side and Cr5Si3 extending toward the Si-rich side from the stoichiometry. The CrSi and CrSi2 phases were considered line compounds with no solubility range, and the solubility of Cr in the Si phase was ignored. A set of self-consistent thermodynamic parameters for the Cr–Si system was obtained using the CALPHAD technique. The phase diagrams calculated using the optimized parameters showed reasonable agreement with the latest phase equilibrium data and thermodynamic property data in the literature, including the enthalpy of mixing, formation enthalpy, and chemical potential diagrams of Cr and Si in the equilibrium phases.

Computing formation enthalpies through an explainable machine learning method: the case of lanthanide orthophosphates solid solutions

In the last decade, the use of AI in Condensed Matter physics has seen a steep increase in the number of problems tackled and methods employed. A number of distinct Machine Learning approaches have been employed in many different topics; from prediction of material properties to computation of Density Functional Theory potentials and inter-atomic force fields. In many cases, the result is a surrogate model which returns promising predictions but is opaque on the inner mechanisms of its success. On the other hand, the typical practitioner looks for answers that are explainable and provide a clear insight into the mechanisms governing a physical phenomena. In this study, we describe a proposal to use a sophisticated combination of traditional Machine Learning methods to obtain an explainable model that outputs an explicit functional formulation for the material property of interest. We demonstrate the effectiveness of our methodology in deriving a new highly accurate expression for the enthalpy of formation of solid solutions of lanthanide orthophosphates.

Comparative study on the equation of state of detonation products

The equation of state (EOS) for detonation products can predict explosive performance with basic information about density, enthalpy of formation, and elemental composition. However, to achieve higher prediction accuracy, it is necessary to select an appropriate EOS for the specific detonation parameters being calculated. To study the applicability of different equations of states for explosive products, five EOSs, Becker–Kistiakowsky–Wilson, Kihara–Hikita–Tanaka, Virial-Wu (VLW), Lennard-Jones–Devonshire (LJD), and Jacobs–Cowperthwaite–Zwisler (JCZ), were used to calculate the Hugoniot curve of nitrogen and the detonation performance of typical explosives. The calculation results show that all five EOSs can provide reasonably accurate predictions of the Hugoniot curve of nitrogen on the relative volume-pressure plane. Moreover, the EOSs can accurately predict the detonation velocity and pressure of explosives within a wide range of initial densities. When it comes to temperature calculations, LJD and JCZ demonstrate higher prediction accuracy. Additionally, the results indicate that VLW may not be suitable for calculating the overdriven detonation of explosives, particularly at higher pressures.

First-principles prediction on the structural stability, electronic, optical and mechanical properties of TiBC, Ti6Si2B and Ti6Ge2B

The crystal structure stability, mechanical, optical and thermodynamic properties of TiBC, Ti6Si2B and Ti6Ge2B were predicted using the first principles calculations. The analysis of phonon dispersion curves, formation enthalpies, energy bands, and density of states demonstrate that TiBC, Ti6Si2B and Ti6Ge2B exhibit structure stability and metallic properties. The tensile strength of TiBC, Ti6Si2B and Ti6Ge2B were simulated, the results showed that the tensile strength of TiBC was the best. Anisotropy was explored by anisotropy index, 3D surface constructions and 2D projections. The order of anisotropy is TiBC > Ti6Ge2B > Ti6Si2B. The optical properties showed that TiBC, Ti6Si2B and Ti6Ge2B have strong long-wave absorption capacity. Finally, Debye temperature and sound velocity were investigated, the order of Debye temperature is: TiBC > Ti6Si2B > Ti6Ge2B.

Chemical space deconstruction-based dynamic model ensemble architecture for molecular property prediction

Green solvents, catalysts, functional materials, drugs, and other chemical products now have a quick engine for design thanks to machine learning (ML) based prediction of molecular properties. However, the accuracy and stability of ML-based models can be impeded by poor data quality, which is rarely studied in chemical product discovery and design. Inspired by the dynamic ensemble selection (DES), an improved DES based on chemical space deconstruction is proposed in this work to accommodate the prediction task of molecular properties. We innovatively developed a chemical space representation and deconstruction model based on a self-organizing mapping (SOM) neural network, facilitating the rapid implementation of the improved DES on molecular samples. Consequently, a novel dynamic model ensemble architecture (SOM-DES) is proposed as a model enhancement technology to build a more accurate and stable ensemble model, aiming to improve the predictive performance on the chemical subspace within poor-quality data. To achieve the architecture, a supervised dimensionality reduction algorithm has been improved to enhance the deep mining of molecular feature information for DES optimization. Additionally, a novel resampling strategy based on the combination of the geometric synthetic minority oversampling technique (G-SMOTE) algorithm and chemical space deconstruction, as a data augmentation technology, has been proposed for mitigating the disadvantage of unbalanced data during DES training. The prediction task for enthalpy of formation of the ideal gas is applied as a case study to demonstrate the superiority of the proposed SOM-DES. The results indicate that the proposed SOM-DES (R2 = 0.9731, RMSE = 55.4639) outperforms the traditional static ensemble strategy (SES, R2 = 0.9552, RMSE = 71.5045) in terms of global chemical spatial precision. More importantly, for chemical subspaces that are difficult to predict due to low data quality, SOM-DES shows a significant reduction in prediction errors compared to SES

Визуализация структуры супрамолекулярного комплекса 4-DASPI с кукурбитурилом для предсказания сольватохромного сдвига спектра поглощения

The study of supramolecular “host-guest” complexes in solutions is of fundamental and practical significance. The structures and formation enthalpy of supramolecular complexes for the 4-DASPI dye with two cavitands (cucurbit[6]uril and cucurbit[7]uril) have been obtained by the TDDFT quantum chemistry method with a camb3lyp basis. It was shown by visualization of the structures that the size of cucurbit[6]uril is too small and doesn’t allow the dye chromophore to penetrate into the cavitand cavity while the dye stays in the ground state, but the formation of an external complex is possible. On the contrary, formation of an inclusion complex with the cucurbit[7]uril is energetically favorable, and the dye chromophore penetrates into the cavity. Visualization of the complex structure allows us to determine the chromophore position relative to the given cavitand cavity, and thus we can predict the changes in the dye spectra due to complexation. The theoretical results of the work are in good correlation with the experiment.

In-situ synthesis of dual-phase nitrides and multiple strengthening mechanisms in FeCoCrNiAl0.5 high entropy matrix composite coatings by laser cladding and plasma nitriding

To enhance the wear resistance of high entropy alloy (HEA) coatings and broaden their applications under extreme conditions, this study proposed an in-situ synthesis process of a dual-phase strengthened nitrides layer on laser cladded HEA coating. The microstructural evolution and mechanical properties of FeCoCrNiAl0.5 HEA coating by plasma nitriding were systematically investigated, revealing formation and strengthening mechanisms of nitrides. In comparison to the traditional nitrided substrate 38CrMoAl, the results showed that the nitrided HEA coating exhibited high hardness and wear resistance, characterized by dual-phase nitrides AlN+CrN due to the negative Gibbs free energy, negative nitride formation enthalpy and higher atomic specific surface areas. While only a single-phase iron nitride with lower hardness was obtained on the nitrided 38CrMoAl. The microhardness and wear mass loss of the nitrided HEA coating were 1167 HV and 0.435×10-6mg/mm, respectively, which were 33.4% higher and 63.3% lower than those of the nitrided 38CrMoAl. The strengthening effects attributed to the refinement of dual-phase nitrides, interstitial solid solution by N atoms, dispersion strengthening by higher proportion of nitrides.

Thermodynamic analysis of cellulose nitration

In this study, the standard formation enthalpies and entropies of cellulose and nitrocellulose samples were determined. These characteristics were used for thermodynamic analysis of bulk nitration of the entire cellulose sample and local nitration only of amorphous domains (ADs) of cellulose. It was found that the reaction of bulk nitration of cellulose up to a substitution degree (DS) of 1.5 is endothermic and determined primarily by the contribution of the temperature-entropy component to the negative Gibbs potential. However, if DS is higher than 1.5, the bulk nitration becomes exothermic and its feasibility is determined by the impact of enthalpy on the Gibbs potential. In the case of local nitration of cellulose ADs, the main contribution to the Gibbs potential is made by the reaction enthalpy that determines the feasibility of this process. It was shown that with the enhancement in DS of nitrocellulose, the negative value of the Gibbs potential of the reaction increases. Thus, the cellulose nitration to higher DS is thermodynamically favorable. Since the locally nitrated samples are copolymers of amorphous nitrocellulose and crystalline cellulose, they should be significantly less hydrophilic than cellulose. Therefore, it can be expected that the local nitration method will find a wide practical application for inexpensive hydrophobization of cellulose materials.

Effective hydrogen storage in Na2(Be/Mg)H4 hydrides: Perspective from density functional theory

The utilization of hydrogen energy has garnered significant attention as a viable and environmentally friendly energy alternative. However, there exist some technological challenges pertaining to the storage of hydrogen. In this context, the present study utilizes first-principles calculations to examine the physical characteristics of Na2(Be/Mg)H4 hydrides to better understand their potential for use in hydrogen storage applications. The structure stability of Na2BeH4 and Na2MgH4 hydrides is assessed by formation enthalpy and phonon dispersion calculations. Elastic constants have been utilized to determine the elastic and mechanical stabilities of the studied hydrides. Both hydrides satisfy the established Born stability criteria, suggesting that both Na2BeH4 and Na2MgH4 are mechanically stable compounds. The assessment of electronic properties reveals that Na2BeH4 and Na2MgH4 have semiconducting characteristics with direct and indirect band gaps of 2.22 and 3.10 eV, respectively. Furthermore, various optical characteristics have been evaluated and compared. The computed values of gravimetric and volumetric hydrogen storage capacities for Na2BeH4 (Na2MgH4) hydrides are 6.78 (5.38) wt% and 85.11 (62.78) gH2l−1, respectively, fulfilling the standard set by US-DOE for 2025. This study suggests that both Na2BeH4 and Na2MgH4 hydrides have the potential to be an incredibly efficient choice for solid-state hydrogen storage.

Kinetics of direct and water‐mediated tautomerization reactions of five‐membered cyclic amides or lactams

AbstractAs part of a series of studies of hydrogen‐atom transfer or tautomerization reactions of imidic acid–amide species, , we report the rate constants for a set of 24 five‐membered cyclic compounds at low, 50–300 K, and high, 500–1500 K, temperatures. These rate constants are for both the high temperature direct reaction and for that mediated by an additional water molecule which facilitates the hydrogen transfer reaction at low temperatures. In the latter case we show that the rate of reaction from a pre‐reaction complex can be rapid at temperatures down to 50 K on a 1 ms timescale and is dominated by quantum mechanical effects as evaluated by small‐curvature and quantised‐reaction‐states tunnelling. In addition, we present thermochemical data such as enthalpies of formation, entropies, isobaric heat capacities and enthalpy functions for these largely unknown species which span a range of compounds from pyrolidinone to oxo‐tetrazoles.

Developing the insight for systematic exploration of hydrogen storage in RbMgF3

In the present work, the density functional theory calculation has been performed for RbMgF3-xHx with GGA-PBE approximation implemented in CASTEP code. First time the structural, mechanical, electronic and optical properties of perovskite RbMgF3-xHx (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.65, 1.80, 1.95, 2.25, 2.55, 2.85 and 3.0) has been investigated in details along with hydrogen storage applications. The results of formation enthalpy and elastic constants indicate that the materials are synthesizable. It has been found that the concentration of hydrogen storage decreases the elastic moduli and anisotropy whereas the bandgap becomes narrow because of the shifting of conduction band toward the fermi level. This indicates that hydrogen inclusion altered the electronic properties of the material and material can also be used in various optoelectronic devices alongwith hydrogen storage application. The crystal structure shifted from cubic to tetragonal during the hydrogen storage. The optical properties were thoroughly investigated between 0 and 10 eV. It has been found optical properties are enhanced with the doping concentration of hydrogen, which makes them good candidates for optoelectronic devices. The gravimetric ratio of hydrogen increased up to 2.61% with hydrogen incorporation. The presented material is an efficient material not only for opto-electronic applications but also for hydrogen storage as well.

CO2 -ის დაჭერის პროცესში, ნამწვი აირები - კლინოფთილოლითი დისპერსულ სისტემაში მოსალოდნელ პროცესთა თერმოდინამიკური პროგნოზირება

CO2 generated in production processes and emitted into the atmosphere with flue gases is the cause of the greenhouse effect and negative processes of global climate change towards warming. Therefore, prevention of CO2 emissions into the atmosphere is the research topic of the article. CCUS type climate change mitigation projects are being developed in Georgia, where natural zeolite mineral containing clinoptilolite, Khekordzula tuff is a sorbent for CO2 capture. Its formation enthalpy (ΔfH0 298), Gibbs free energy (ΔfG0 298), and entropy (ΔfS 0 298) have not been studied, also temperatures of its thermal dehydration, CO2 adsorption, expected chemisorption and other thermodynamic quantities. It was determined: Enthalpy of clinoptilolite tuff formation (ΔfH0 298=-39826 kJ/mol), Gibbs free energy (ΔfG0 298=-36735 kJ/mol), entropy (ΔfS 0 298=-10.37 kJ/K-mol); Temperatures of dehydration (94.800C), CO2 capture using it (physical-96.5700C), start of chemo-sorption (95.2400C) and pressure corresponding to these temperatures (745, 636, 534) mm Hg. Tuff can be successfully used for CCUS from flue gases.

First-principles calculations to investigate the structural stability, electronic and mechanical properties of CuGa2 and Cu9Ga4

This paper aims to evaluate the service reliability of intermetallic compounds (IMCs) in Cu-Ga joints. It accomplished this by calculating the thermodynamic and mechanical properties of CuGa2 and Cu9Ga4, which are common IMCs in Cu-Ga low temperature interface reaction, based on the first-principles calculation. According to the calculation results of enthalpy of formation and binding energy, both CuGa2 and Cu9Ga4 are thermodynamically stable, and Cu9Ga4 exhibits superior thermodynamic stability compared to CuGa2. The mechanical properties of Cu9Ga4 are better than CuGa2, with larger bulk modulus, shear modulus and Young's modulus. By comparing the elastic modulus with that of IMCs of Cu-Sn system, Cu9Ga4 shows larger elastic modulus than η′-Cu6Sn5 and smaller than Cu3Sn. In addition, Cu9Ga4 exhibits excellent toughness. By fitting the thermal expansion coefficients of Cu, CuGa2 and Cu9Ga4, the result shows that the thermal expansion coefficients of Cu and Cu9Ga4 are better matched. Additionally, the rapid volume expansion of CuGa2 weakens the interaction force between its atoms, resulting in a faster decay of its bulk modulus. The prediction of the mechanical properties of Cu-Ga compounds provides a deeper understanding of their properties and is important for the understanding of the feasibility of low-temperature brazing of Cu-Ga soldering systems.

Using small database and energy descriptors to predict molecular thermodynamic energies through mediated learning models

Delta machine learning (DML) models have paved a new way to obtaining high fidelity ab initio simulation results of materials by using quantities with lower computational cost as learning materials. However, the low out-of-sample extrapolative ability and the requirement of large training sets have limited broader applications of conventional DML models. In this work, we proposed the concept of non-trivial electron energy, an intermediary energy quantity decoded from the electron total energy but exhibiting high Pearson's correlation with various thermodynamic energies, to build up mediated machine learning (MML) models. By hybridizing the intermediary non-trivial electron energy (N) with a bond descriptor (B) and a spatial matrix (S) of organic molecules, our integrated NBS descriptor shows excellent predictive power of thermodynamic energies with errors close to 1 kcal/mol for MML models when trained by a database with 100 entries and tested by a database with 500 entries. Moreover, adding supplemental sets with 10 ∼ 20 entries into the original training set could greatly improve the out-of-sample extendibility of NBS MML models, such as the molecules with obviously larger size, with disparate bond-type, and even with different elemental compositions. The method of mediated learning provides alternative ways to breakthrough limitations of traditional DML models and can be applied conveniently to study formation enthalpy, thermodynamic energy barriers, multi-dimensional Gibbs free energy surface, and other quantum chemical quantities related to materials' internal energy, enthalpy, and free energy under various conditions at tunable training cost, prediction efficiency, and accuracy.

Structural, mechanical, electronic and thermodynamic properties of YBC, YB2C, YB2C2, Y2B3C2 intermetallics

Transition metal diboride and transition metal boron-carbon intermetallics have attracted extensive attention. In this work, we adopted the first-principles method to reveal the structural stability, elastic behavior, anisotropy and electronic structures of transition metal boron-carbon intermetallics (YBC, YB2C, YB2C2, Y2B3C2). The formation enthalpy suggests that YB2, YBC, YB2C, YB2C2 and Y2B3C2 are thermodynamically stable. The calculated results of elastic constants indicates that all five intermetallics exhibit the mechanical stability. The band structures and density of states indicate that YB2, YBC, YB2C, YB2C2 and Y2B3C2 possess metallic properties. According to v and G/B, these intermetallics exhibit the brittleness. The 3D and 2D maps display the anisotropic properties. Moreover, the Debye temperature θD of YB2, YBC, YB2C, YB2C2 and Y2B3C2 at high temperatures obeys the order of YBC> YB2C2> YB2C > Y2B3C2 > YB2.

First-principles analysis of physical properties of the novel calcium-based hydrides for hydrogen storage application

The current work aims to investigate the physical properties of the new calcium-based perovskite hydride CaXH3 (X=Cu, and Zn) for hydrogen storage applications using DFT studies. Both materials were found to be thermodynamically and mechanically stable owing to their negative formation enthalpies, cohesive energy, and elastic constants. The absence of negative frequencies in the phonon dispersion curve reveals the dynamic stability of the structure. The optimized structure lattice constants were found 3.62Å, and 3.78Å with a bulk modulus of 117.40, and 82.39 GPa, respectively. The Poisson and Pugh ratios were confirmed to have ionic bonding, while the Cauchy difference and Pugh ratio (B/G) results exhibited the brittle behavior of both materials. In addition, both materials have anisotropic characteristics, and CaCuH3 is stiffer than CaZnH3. The electronic properties confirmed that both compounds have a metallic nature owing to the zero band gap and high contribution of the Ca and X (Cu, Zn) d states near the Fermi level. These compounds were found non-magnetic by the investigation of magnetic properties. The optical results indicate that CaZnH3 plays a significant role in optoelectronics, solar cells, and photonics applications because of its higher conductivity, refractive index, dielectric function, and reflectivity, as well as its higher adsorption than CaCuH3.The hydrogen storage capacities of CaCuH3 and CaZnH3 hydrides were calculated to be 2.88 wt. % and 2.75 wt.%, respectively, and it was predicted that both compounds have the potential to store hydrogen, as evidenced by storage application.