Debye model

About: Debye model is a research topic. Over the lifetime, 7462 publications have been published within this topic receiving 133987 citations.

Nonperturbative Debye Mass in Finite Temperature QCD

Abstract: QCD matter, a spatially and temporally extended sys- tem of matter described by the laws of Quantum Chro- modynamics, goes at high temperatures into a quark- gluon plasma phase, in which color is no more confined and chiral symmetry is restored An essential quantity, describing coherent static interactions in the plasma, is the inverse screening length of color electric fields, the Debye mass mD The Debye mass enters in many essen- tial characteristics of static properties of the plasma Its numerical value is important for phenomenological dis- cussions of formation of the quark-gluon plasma, for the analysis of J/� andsuppression in heavy ion colli- sions, for the computation of parton equilibration rates, etc (see, eg (1)) The definition and computation of the Debye mass for abelian QED plasma is well understood (2) The electro- magnetic current jµ is a gauge-invariant quantity, and the Debye mass can be extracted from the 2-point gauge invariant correlation function of j0 in the plasma There are no massless charged particles in QED, which allows an infrared-safe perturbative computation of the Debye mass in powers of the electromagnetic coupling e This has been done to order e 5 (3) The situation in QCD is much more complicated First, the corresponding cur- rent in QCD, j a , is not a gauge invariant quantity Sec- ond, there are massless charged gluons which give rise to infrared divergences and prevent the perturbative deter- mination of the Debye mass beyond leading order A non-perturbative gauge invariant definition of the Debye mass in vectorlike theories with zero chemical po- tential was suggested in (4) According to it, mD can be defined from the large distance exponential fall-off of correlators of gauge-invariant time-reflection odd opera- tors O, h O(τ, ~ x)O(τ,0)i ∼ C|~

Structural, mechanical and electronic properties of 3d transition metal nitrides in cubic zincblende, rocksalt and cesium chloride structures: a first-principles investigation.

Abstract: We report systematic results from ab initio calculations with density functional theory on three cubic structures, zincblende (zb), rocksalt (rs) and cesium chloride (cc), of the ten 3d transition metal nitrides. We computed lattice constants, elastic constants, their derived moduli and ratios that characterize mechanical properties. Experimental measurements exist in the literature of lattice constants for rs-ScN, rs-TiN and rs-VN and of elastic constants for rs-TiN and rs-VN, all of which are in good agreement with our computational results. Similarly, computed Vickers hardness (HV) values for rs-TiN and rs-VN are consistent with earlier experimental results. Several trends were observed in our rich data set of 30 compounds. All nitrides, except for zb-CrN, rs-MnN, rs-FeN, cc-ScN, cc-CrN, cc-NiN and cc-ZnN, were found to be mechanically stable. A clear correlation in the atomic density with the bulk modulus (B) was observed with maximum values of B around FeN, MnN and CrN. The shear modulus, Young’s modulus, HV and indicators of brittleness showed similar trends and all showed maxima for cc-VN. The calculated value of HV for cc-VN was about 30 GPa, while the next highest values were for rs-ScN and rs-TiN, about 24 GPa. A relation (HV/ 2 D ) between HV and Debye temperature ( D) was investigated and verified for each structure type. A tendency for anti-correlation of the elastic constant C44, which strongly influences stability and hardness, with the number of electronic states around the Fermi energy was observed. (Some figures may appear in colour only in the online journal)

Elastic, electronic, optical and thermodynamic properties of Ba3Ca2Si2N6 semiconductor: First-principles predictions

Abstract: In this paper, we present and discuss the results of first-principles calculations of the structural, electronic, optical, elastic and thermodynamic properties of the monoclinic quaternary nitride Ba3Ca2Si2N6. A comparison between the computed crystal structure parameters and the corresponding experimental counterparts shows a very good agreement between them. The elastic constants were evaluated numerically for the monocrystalline and polycrystalline Ba3Ca2Si2N6 using the strain–stress approach. The predicted elastic constants demonstrate that Ba3Ca2Si2N6 is soft, ductile and mechanically stable. Ba3Ca2Si2N6 shows a strong anisotropic behavior of the elastic and structural properties. The calculated band structure reveals a semiconductor character of Ba3Ca2Si2N6. The spectra of the macroscopic linear optical functions, namely the complex dielectric function, reflection coefficient, energy loss of electrons, absorption coefficient and complex refractive index, were calculated and discussed. The quasi-harmonic Debye model was used to explore the temperature and pressure dependencies of certain macroscopic physical parameters for Ba3Ca2Si2N6.

Singular behavior of the Debye-Waller factor of graphene

Abstract: It is shown that the mean-square displacement or the exponent of the Debye-Waller factor of graphene has a singularity except at zero temperature. The zero-temperature values of the mean-square displacement are calculated separately for planar and out-of-plane phonon modes for graphene. These values give the DebyeWaller factor that can be used to model various scattering processes at temperatures much lower than the Debye temperature of graphene. Since the Debye temperature of graphene is about 2300 K for planar modes, the calculated values should provide a useful estimate of the Debye-Waller factor at temperatures of practical interest. Finally, it is shown qualitatively that the singularity can be removed by accounting for the finite size of real graphene crystals.