Specific Heat Cv Research Articles

Hybrid density functional study on lattice vibration, thermodynamic properties, and chemical bonding of plutonium monocarbide**Project supported by the National Natural Science Foundation of China (Grant Nos. 21371160 and 21401173).

Hybrid density functional theory is employed to systematically investigate the structural, magnetic, vibrational, thermodynamic properties of plutonium monocarbide (PuC and PuC0.75). For comparison, the results obtained by DFT, DFT + U are also given. For PuC and PuC0.75, Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic (AFM) structure. The calculated phonon spectra suggest that PuC and PuC0.75 are dynamically stable. Values of the Helmholtz free energy ΔF, internal energy ΔE, entropy S, and constant-volume specific heat Cv of PuC and PuC0.75 are given. The results are in good agreement with available experimental or theoretical data. As for the chemical bonding nature, the difference charge densities, the partial densities of states and the Bader charge analysis suggest that the Pu–C bonds of PuC and PuC0.75 have a mixture of covalent character and ionic character. The effect of carbon vacancy on the chemical bonding is also discussed in detail. We expect that our study can provide some useful reference for further experimental research on the phonon density of states, thermodynamic properties of the plutonium monocarbide.

First-principles investigations on the phase stability, elastic and thermodynamic properties of Zr–Al alloys

In this paper, we employ first-principles methods based on electronic density functional theory (DFT) to investigate the phase stability, elastic and thermodynamic properties of Zr – Al binary substitutional alloys which are Zr 3 Al , Zr 2 Al , ZrAl , ZrAl 2 and ZrAl 3. By analyzing the elastic constants and enthalpy of formation, those phases both satisfy the generalized stability criteria and the results show that ZrAl 2 is the most stable. Due to high bulk modulus B, shear modulus G and Youngs modulus Y, ZrAl 2 also possesses excellent mechanical properties. Moreover, it is expected that there will be covalent bonding between Zr and Al atom in ZrAl 2 compound, which is confirmed by the electronic structure and the differences of charge density discussions. In the end, based on the calculated elastic modulus, the elastic wave velocity, Debye temperature ΘD and specific heat CV are discussed. As a result, ZrAl 3 possesses the highest Debye temperature and sound velocity, meaning a larger associated thermal conductivity and higher melting temperature.

Thermodynamics of anisotropic triangular magnets with ferro- and antiferromagnetic exchange

We investigate thermodynamic properties like specific heat cV and susceptibility χ in anisotropic J1–J2 triangular quantum spin systems (). As a universal tool we apply the finite temperature Lanczos method (FTLM) based on exact diagonalization of finite clusters with periodic boundary conditions. We use clusters up to N = 28 sites where the thermodynamic limit behavior is already stably reproduced. As a reference we also present the full diagonalization of a small eight-site cluster. After introducing model and method we discuss our main results on cV(T) and . We show the variation of peak position and peak height of these quantities as function of control parameter . We demonstrate that maximum peak positions and heights in Néel phase and spiral phases are strongly asymmetric, much more than in the square lattice J1–J2 model. Our results also suggest a tendency to a second side maximum or shoulder formation at lower temperature for certain ranges of the control parameter. We finally explicitly determine the exchange model of the prominent triangular magnets Cs2CuCl4 and Cs2CuBr4 from our FTLM results.

Theory of competitive solvation of polymers by two solvents and entropy-enthalpy compensation in the solvation free energy upon dilution with the second solvent.

We develop a statistical mechanical lattice theory for polymer solvation by a pair of relatively low molar mass solvents that compete for binding to the polymer backbone. A theory for the equilibrium mixture of solvated polymer clusters {AiBCj} and free unassociated molecules A, B, and C is formulated in the spirit of Flory-Huggins mean-field approximation. This theoretical framework enables us to derive expressions for the boundaries for phase stability (spinodals) and other basic properties of these polymer solutions: the internal energy U, entropy S, specific heat CV, extent of solvation Φsolv, average degree of solvation 〈Nsolv〉, and second osmotic virial coefficient B2 as functions of temperature and the composition of the mixture. Our theory predicts many new phenomena, but the current paper applies the theory to describe the entropy-enthalpy compensation in the free energy of polymer solvation, a phenomenon observed for many years without theoretical explanation and with significant relevance to liquid chromatography and other polymer separation methods.

The Structural, Dielectric, Lattice Dynamical and Thermodynamic Properties of Zinc-Blende CdX (X=S, Se, Te) from First-Principles Analysis**Supported by the National Natural Science Foundation of China under Grant No 11374217.

The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX (X=S, Se, Te) are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the published experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal optical-transverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX (X=S, Se, Te) are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX (X=S, Se, Te) and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.

On dependences of the thermoelastic properties on size and shape of an iron nanocrystal

Dependences of the elastic modulus (BT), Poisson ratio (μ), thermal expansion coefficient (αp), and specific heat (cv and cp) on the size and shape of the simple matter nanocrystal with a free surface have been studied using the model of nanocrystal in the form of a rectangular parallelepiped with a variable surface shape (RP model). Specific calculations have been carried out for bcc iron. It is shown that the elastic modulus decreases with an isomorphic (at a constant nanocrystal shape) decrease in the nanocrystal size (number N of atoms), whereas the functions μ(N), αp(N), cv(N), cp(N), and cp(N)-cv(N) increase along the isotherm. The larger the deviation of the nanocrystal shape is from the most energetically stable form (cube for the RP model), the more noticeably the change in these functions is with a decrease in nanocrystal size along the isotherm. It is shown that the size compression of the lattice parameter for a bcc iron nanocrystal increases with a decrease in the nanocrystal size, with a decrease in temperature, or with an increase in the nanocrystal shape deviation from the most energetically stable form.

First-principles calculations of phonon and thermodynamic properties of OsSi2

The structure, lattice dynamics, and some thermodynamic properties of orthorhombic OsSi2 were investigated using a first-principles density functional theory (DFT). Linear response theory was used to calculate the phonon dispersion relation and phonon density of states for OsSi2 as well as its infrared and Raman active mode frequencies. In this study, the thermodynamic properties, including vibrational entropy (Svib), constant-volume specific heat (Cv), and Debye temperature (ΘD), were predicted theoretically and discussed.

Field-enhanced electronic specific heat of carbon nanotubes

The tight-binding model including curvature effects is used to study the effect of transverse electric field on the low-temperature electronic specific heat (Cv) for armchair and zigzag carbon nanotubes (ACNTs and ZCNTs). Electric field could effectively modulate energy dispersions of CNTs and cause a shift of electronic states toward the Fermi energy. As field strength reaches to a critical value (Fc), it induces special structures in the density of states near the Fermi energy and thus the giant specific heat. At Fcs, Cv has a value comparable to that of the phonon specific heat and reveals strongly non-linear dependence on temperature. The critical field strength and giant specific heat are closely related to nanotube's geometry. Moreover, under Fcs, the extra longitudinal magnetic flux could cause a re-enhancement in Cv for ZCNTs, whereas Cv is always diminished for ACNTs.

Investigation of structural, elastic, and lattice-dynamical properties of Ca2Si, Ca2Ge, and Ca2Sn based on first-principles density functional theory

The structural, elastic, phonon and thermodynamic properties of orthorhombic Ca2X (X=Si, Ge, and Sn) were systematically investigated using first-principles density functional theory (DFT). The elastic constants (cij), elastic modulus (B, G, E), Poisson’s ratio (ν), and elastic Debye temperature (ΘD) were determined and compared with the results of previous calculations. For the first time, linear response theory is used to calculate the phonon dispersion relation and phonon density of states for these compounds as well as their infrared and Raman active mode frequencies. In this study, the thermodynamic properties such as vibrational entropy (Svib) and constant-volume specific heat (Cv) were predicted theoretically and discussed.

До теорії силових сталих багатоатомних систем у моделі сильного зв’язку (частина ІІ)

An approximate expression for the Coulomb interaction energy in solids has been obtained in the framework of the tight-binding model. The condition of adiabatic approximation and the procedure of quantum statistical averaging for the first (static) term in the expansion of the average potential energy in small nuclear shifts are analyzed, which allowed the electron contribution to the thermal expansion of solids to be calculated. An equation of state for a solid is obtained in the harmonic approximation by analyzing the internal energy and the thermal properties of the solid. A relationship between the specific heats Cv and Cp, which agrees with the Gr¨uneisen law, is found.

Exact Solution to the Extended Zwanzig Model for Quasi-Sigmoidal Chemically Induced Denaturation Profiles: Specific Heat and Configurational Entropy

Temperature and chemically induced denaturation comprise two of the most characteristic mechanisms to achieve the passage from the native state N to any of the unstructured states Dj in the denatured ensemble in proteins and peptides. In this work we present a full analytical solution for the configurational partition function 𝒵qs of a homopolymer chain poly-X in the extended Zwanzig model (EZM) for a quasisigmoidal denaturation profile. This solution is built up from an EZM exact solution in the case where the fraction α of native contacts follows exact linear dependence on denaturant’s concentration ζ; thus an analytical solution for 𝒵L in the case of an exact linear denaturation profile is also provided. A recently established connection between the number ν of potential nonnative conformations per residue and temperature-independent helical propensity ω complements the model in order to identify specific proteinogenic poly-X chains, where X represents any of the twenty naturally occurring aminoacid residues. From 𝒵qs, equilibrium thermodynamic potentials like entropy 𝒮 and average internal energy 〈E〉 and thermodynamic susceptibilities like specific heat C𝓋 are calculated for poly-valine (poly-V) and poly-alanine (poly-A) chains. The influence of the rate at which native contacts denature as function of ζ on thermodynamic stability is also discussed.

Ab initio study of the structural, mechanical, and dynamical properties of the rare-earth dihydrides XH2 (X=Sc, Y, and La)

The structural, electronic, mechanical, dynamical and thermodynamic properties of rare-earth dihydrides XH2 (X=Sc, Y, and La) with the cubic fluorite structure have been systematically investigated by using the projector augmented wave (PAW) method within the generalized-gradient approximation. The calculated lattice parameters, electronic structures and elastic constants of XH2 agree well with available experimental data and other theoretical results. Both the lattice constants and the equilibrium unit cell volumes increase in accordance with heavier rare-earth atom. From the obtained bulk modulus, shear modulus and Young's modulus, the resistance to volume change, shear deformations, and even tensile and compressive deformations weakens from ScH2 to LaH2 successively. The brittle/ductile properties of the three compounds are determined by the ratio of B/G and the Cauchy pressure C12−C44. Poisson's ratio, elastic anisotropy factor, Debye temperature, and sound velocities of XH2 are also predicted. Especially, the phonon dispersion curves and corresponding phonon density of states of XH2 are determined using a linear-response approach to density functional perturbation theory (DFPT) successfully, the phonon frequencies (in THz) obtained at the zone-center (Γ-point) for infrared-active modes T1u and Raman-active modes T2g are ScH2: T1u=29.294, T2g=35.279; YH2: T1u=27.295, T2g=32.624; and LaH2: T1u=24.286, T2g=28.004. Our results show that the three compounds can be stabilized dynamically and mechanically in the ground state phase of the cubic fluorite structure. The thermodynamic functions such as phonon contributions to the internal energy E, the Helmholtz free energy F, the entropy S, the changes of H–H298.15 and G–G298.15 and the constant volume specific heat CV under high temperatures are also obtained based on phonon density of states.

Scaling Regimes and the Singularity of Specific Heat in the 3D Ising Model

AbstractThe singularity of specific heatCVof the three-dimensional Ising model is studied based on Monte Carlo data for lattice sizesL≤1536. Fits of two data sets, one corresponding to certain value of the Binder cumulant and the other — to the maximum ofCV, provide consistent values ofC0in the ansatzCV(L)=C0+ALα/νat largeL, ifα/ν=0.196(6). However, a direct estimation from ourdata suggests thatα/ν, most probably, has a smaller value (e.g.,α/ν= 0.113(30)). Thus, the conventional power-law scaling ansatz can be questioned because of this inconsistency. We have found that the data are well described by certain logarithmic ansatz.

Solvation of polymers as mutual association. II. Basic thermodynamic properties

The theory of equilibrium solvation of polymers B by a relatively low molar mass solvent A, developed in the simplest form in Paper I, is used to explore some essential trends in basic thermodynamic properties of solvated polymer solutions, such as the equilibrium concentrations of solvated polymers AiB and free solvent molecules A, the mass distribution φ(AiB)(i) of solvated clusters, the extent of solvation of the polymer Φ(solv), the solvation transition lines T(solv)(φB(o)), the specific heat C(V), the osmotic second virial coefficient B2, phase stability boundaries, and the critical temperatures associated with closed loop phase diagrams. We discuss the differences between the basic thermodynamic properties of solvated polymers and those derived previously for hierarchical mutual association processes involving the association of two different species A and B into AB complexes and the subsequent polymerization of these AB complexes into linear polymeric structures. The properties of solvated polymer solutions are also compared to those for solutions of polymers in a self-associating solvent. Closed loop phase diagrams for solvated polymer solutions arise in the theory from the competition between the associative and van der Waals interactions, a behavior also typical for dispersed molecular and nanoparticle species that strongly associate with the host fluid. Our analysis of the temperature dependence of the second osmotic virial coefficient reveals that the theory must be generalized to describe the association of multiple solvent molecules with each chain monomer, and this complex extension of the present model will be developed in subsequent papers aimed at a quantitative rather than qualitative treatment of solvated polymer solutions.

Molecular dynamics study of one-component soft-core system: thermodynamic properties in the supercooled liquid and glassy states.

Molecular dynamics simulations were performed to study the thermal properties of a supercooled liquid near the glass transition regime and of glasses in a one-component soft-core system with the pair potential φn(r) = ɛ(σ/r)(n), in which n = 12. The results are examined along a phase diagram, in which the compressibility factor defined by [Formula: see text] is plotted against the reduced density ρ* = ρ(ɛ/kBT)(3/n) (or the reduced temperature T* = ρ*(-n/3)). Similarly, a time-dependent dynamical compressibility factor can be plotted against the time-dependent reduced density [Formula: see text] (or the reduced time-dependent temperature). Analytical expressions of the specific heats CV and CP and of the entropy, S, were obtained as a function of [Formula: see text] or of the scaled potential U*. Even for a rapid cooling process, the CV values are found to be affected by non-equilibrium relaxations in the [Formula: see text] region, where [Formula: see text] is the given initial value of [Formula: see text]. The problem of the Kauzmann paradox is discussed using these expressions. The fluctuation of the time-dependent temperature, Tt*, which determines CV, is characterized by the spectra that are obtained by multitaper methods. The thermal fluctuation along the non-equilibrium relaxation under NVE conditions was also examined.

Phase transitions in a spinless, extended Falicov–Kimball model on the triangular lattice

A numerical diagonalization technique with canonical Monte-Carlo simulation algorithm is used to study the phase transitions from low temperature (ordered) phase to high temperature (disordered) phase of spinless Falicov–Kimball model on a triangular lattice with correlated hopping (t′). It is observed that the low temperature ordered phases (i.e. regular, bounded and segregated) persist up to a finite critical temperature (Tc). In addition, we observe that the critical temperature decreases with increasing the correlated hopping in regular and bounded phases whereas it increases in the segregated phase. Single and multi peak patterns seen in the temperature dependence of specific heat (Cv) and charge susceptibility (χ) for different values of parameters like on-site Coulomb correlation strength (U), correlated hopping (t′) and filling of localized electrons (nf) are also discussed.

Electronic, elastic and thermal properties of SrCu2As2 via first principles calculation

ThCr2Si2-type crystal has a large family member, most of which have certain unusual properties. In this work, the electronic, elastic and thermal properties of the recently re-synthesized SrCu2As2 are investigated by employing first principles calculation. The characters of the band structure and the partial density of states (PDOS) of SrCu2As2 are analyzed, which shows that SrCu2As2 is a metallic crystal with no magnetism. The calculated elastic constants reveal that SrCu2As2 is mechanically stable but anisotropic; the anisotropy is further illustrated by the direction-dependent linear compressibility and Young’s modulus. By analyzing, we find that the corresponding shear deformation is most easy to take place when the shear stresses are imposed on the vertical {100} planes along the horizontal 〈100〉 directions. Besides these, other elasticity-relevant properties, including the bulk modulus, shear modulus, the Poisson ratio, the velocities of acoustic waves and the Debye temperature, are also derived. The specific heat CV and CP as functions of temperature (T) are obtained from quasi-harmonic Debye model, the curve of Cp–T consists well with the experimental data. Meanwhile, the thermal expansion coefficient α is also predicted.

Thermodynamics of ideal proteinogenic homopolymer chains as a function of the energy spectrum E, helical propensity ω and enthalpic energy barrier

A reformulation and generalization of the Zwanzig model (ZW model) for ideal homopolymer chains poly-X, where X represents any of the twenty naturally occurring proteinogenic amino acid residues is presented. This reformulation and generalization provides a direct connection between coarse-grained parameters originally proposed in the ZW model with variables from the Lifson–Roig (LR) theory, such as the helical propensity per residue ω, and new variables introduced here, such as the energy gap Δ between unfolded and folded structures, as well as the ratio f of the energy scales involved. This enables us to discover the relevance of the energy spectrum E to the onset of configurational phase transitions. From the configurational partition function \U0001d4ac, thermodynamic properties such as the configurational entropy S, specific heat Cv and average energy 〈E〉 are calculated in terms of the number of residues K, temperature T, helical propensity ω and energy barrier ΔH for different poly-X chains in vacuo. Results obtained here provide substantial evidence that configurational phase transitions for ideal poly-X chains correspond to first-order phase transitions. An anomalous behavior of the thermodynamic functions 〈E〉, Cv, S with respect to the number K of residues is also highlighted. On-going methods of solution are outlined.

Thermophysical properties of Pr1−xCaxCoO3

In the present paper, the thermophysical properties of PrCoO3 cobaltates is mapped here with reference to the changed local environment at A-site due to calcium doping for the first time using Rigid Ion Model (RIM). The specific heat and there by thermal expansion for temperature (1K≤T≤1000K) of Pr1−xCaxCoO3 (x=0.0–0.5) are presented. The trends of variation of our computed results on specific heat with temperature are in more or less similar with corresponding experimental data for almost all the compositions (x) of Pr1−xCaxCoO3. Strong electron–phonon interactions are present in these compounds which causes the variation of the lattice specific heat (Cv(lattice)) with cation doping of varying size and valence. In addition, we have computed the thermal expansion (α), bulk modulus (B), cohesive energy (ϕ), molecular force constant (ƒ), and Restsrahalen frequency (υ) whose results are discussed in detail.

THE AB INITIO CALCULATION OF THE DYNAMICAL AND THE THERMODYNAMIC PROPERTIES OF THE ZINC-BLENDE GaX (X=N, P, As AND Sb)

By this work, we aim to study the dynamical and the thermodynamic properties of the zinc-blende GaX ( X = N , P , As and Sb ) using the Ab initio simulation method. Indeed, we studied the lattice dynamics, the constant-volume specific heat (Cv), the internal energy (U), the entropy (S) and the free energy (F). The observed differences between the properties of GaX elements were discussed. Our results and the available literature data (theoretical and experimental) seems to be in good agreement. Moreover, Cv, U, F and S were calculated by using the harmonic approximation in the calculation of the dynamic lattice vibration. The good agreement between our results of both the phonon frequency, the constant-volume specific heat and the experimental data allows us to conclude that our results of S, U and F of GaX were well predicted.