Debye model

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

Engineering of the thermodynamic properties of bilayer graphene by atomic plane rotations: the role of the out-of-plane phonons

Abstract: We investigated theoretically the specific heat of graphene, bilayer graphene and twisted bilayer graphene taking into account the exact phonon dispersion and density of states for each polarization branch. It is shown that contrary to a conventional belief the dispersion of the out-of-plane acoustic phonons – referred to as ZA phonons – deviates strongly from a parabolic law starting from the frequencies as low as ∼100 cm−1. This leads to the frequency-dependent ZA phonon density of states and the breakdown of the linear dependence of the specific heat on temperature T. We established that ZA phonons determine the specific heat for T ≤ 200 K while contributions from both in-plane and out-of-plane acoustic phonons are dominant for 200 K ≤ T ≤ 500 K. In the high-temperature limit, T > 1000 K, the optical and acoustic phonons contribute approximately equally to the specific heat. The Debye temperature for graphene and twisted bilayer graphene was calculated to be around ∼1861–1864 K. Our results suggest that the thermodynamic properties of materials such as bilayer graphene can be controlled at the atomic scale by rotation of the sp2-carbon planes.

First-principles investigations on elastic and thermodynamic properties of zinc-blende structure BeS

Abstract: In this paper the elastic and thermodynamic proper-ties of the cubic zinc-blende structure BeS at different pressures and temperatures are investigated by using ab initio plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated results are in excellent agreement with the available experimental data and other theoretical results. It is found that the zinc-blende structure BeS should be unstable above 60GPa. The thermodynamic properties of the zinc-blende structure BeS are predicted by using the quasi-harmonic Debye model. The pressure-volume-temperature (P - V - T) relationship, the variations of the thermal expansion coefficient a and the heat capacity C(V) with pressure P and temperature T, as well as the Gruneisen parameter-pressure-temperature (gamma - P - T) relationship are obtained systematically in the ranges of 0-90GPa and 0-2000K.

Plasma screening effects on the electronic structure of multiply charged Al ions using Debye and ion-sphere models

Abstract: We analyze atomic structures of plasma-embedded aluminum (Al) atom and its ions in the weak- and strong-coupling regimes. The plasma screening effects in these atomic systems are accounted for using the Debye and ion-sphere (IS) potentials for the weakly and strongly coupled plasmas, respectively. Within the Debye model, special attention is given to investigate the spherical and nonspherical plasma screening effects considering in the electron-electron interaction potential. The relativistic coupled-cluster (RCC) method has been employed to describe the relativistic and electronic correlation effects in the above atomic systems. The variations in the ionization potentials (IPs) and excitation energies (EEs) of the plasma-embedded Al ions are presented. It is found that the atomic systems exhibit more stability when the exact screening effects are taken into account. It is also shown that in the presence of a strongly coupled plasma environment, the highly ionized Al ions show blueshifts and redshifts in the spectral lines of the transitions between the states with the same and different principal quantum numbers, respectively. Comparison among the results obtained from the Debye and IS models are also carried out considering similar plasma conditions.

Phonon density of states in iron at high pressures and high temperatures

Abstract: The phonon density of states (DOS) in iron has been measured in situ by nuclear resonance inelastic X-ray scattering (NRIXS) at high pressures and high temperatures in a resistively heated diamond anvil cell. The DOS data provide a variety of thermodynamic and elastic parameters essential for characterizing iron at depth in the Earth interior, such as average sound velocity, Debye temperature, atomic mean square displacement, average kinetic energy, vibrational entropy and specific heat. The NRIXS data were collected at 6, 20, and 29 GPa and at temperatures up to 920 K. Temperatures were directly determined from the measured spectra by the ratio of intensities of the phonon creation/annihilation side bands that are determined only by the Boltzmann factor. The change of the DOS caused by the structural transition from α-Fe to ɛ-Fe is small and not resolvable within the experimental precision. However, the phonon energies in γ-Fe are clearly shifted to lower values with respect to α- and ɛ-Fe. The temperature dependence of derived thermodynamic parameters is presented and compared with those obtained by Debye’s model. The Debye temperatures that best describe the data decrease slightly with increasing temperature.