This work provides the community with an easily executable open-source Python package designed to automize the evaluation of Interfacial Phonons (InterPhon). Its strategy of arbitrarily defining the interfacial region and periodicity alleviates the excessive computational cost in applying ab initio phonon calculations to interfaces and enables efficient extraction of interfacial phonons. InterPhon makes it possible to apply all of the phonon-based predictions that have been available for bulk systems, to interfacial systems. The first example, in which this package was applied to InAs surfaces, demonstrates a systematic structure search for unexplored surface reconstructions, navigated by the imaginary mode of surface phonons. It eventually explains the anisotropic surface vibrations of the polar crystal. The second example, involving oxygen adsorption on Cu, reveals adsorption-induced vibrational change and its contribution to energetic stability. The third example, on a Si/GaAs interface, shows distinct vibrational patterns depending on interfacial structures. It leads to a prediction regarding the structural transition of interfaces and unveils the processing conditions for spontaneous growth of GaAs nanowires on Si. High-level automation in InterPhon will be of great help in elucidating interfacial atomic dynamics and in implementing an automated computational workflow for diverse interfacial systems.
The electron temperature dependent electron density of states, Fermi-Dirac distribution, and electron-phonon spectral function are computed as prerequisites before achieving effective electron-phonon coupling factor. The obtained coupling factor is implemented into a molecular dynamics (MD) and two-temperature model (TTM) coupled simulation of femtosecond laser heating. By monitoring temperature evolutions of electron and lattice subsystems, the result utilizing coupling factor from ab initio calculation, shows a faster decrease of electron temperature and increase of lattice temperature than …
We show that time-dependent density functional theory (TDDFT) is applicable to coherent optical phonon generation by intense laser pulses in solids. The two mechanisms invoked in phenomenological theories, namely impulsively stimulated Raman scattering and displacive excitation, are present in the TDDFT. Taking the example of crystalline Si, we find that the theory reproduces the phenomena observed experimentally: dependence on polarization, strong growth at the direct band gap, and the change of phase from below to above the band gap. We conclude that the TDDFT offers a predictive ab initio f…
The coupling between electrons and phonons in solids plays a central role in describing many phenomena, including superconductivity and thermoelecric transport. Calculations of this coupling are exceedingly demanding as they necessitate integrations over both the electron and phonon momenta, both of which span the Brillouin zone of the crystal, independently. We present here an ab initio method for efficiently calculating electron-phonon mediated transport properties by dramatically accelerating the computation of the double integrals with a dual interpolation technique that combines maximally…
Perturbo is a software package for first-principles calculations of charge transport and ultrafast carrier dynamics in materials. The current version focuses on electron-phonon interactions and can compute phonon-limited transport properties such as the conductivity, carrier mobility and Seebeck coefficient. It can also simulate the ultrafast nonequilibrium electron dynamics in the presence of electron-phonon scattering. Perturbo uses results from density functional theory and density functional perturbation theory calculations as input, and employs Wannier interpolation to reduce the computat…
We present a systematic first-principles study of the phonon spectrum of hexagonal YMnO3 in ferroelectric (multiferroic) phase. We investigated in detail the low-energy phonon modes, their dispersion, symmetry, as well as the infrared optical properties of the crystal and determined the phonon density of states.
In polar semiconductors and oxides, the long-range nature of the electron-phonon (\textit{e}-ph) interaction is a bottleneck to compute charge transport from first principles. Here, we develop an efficient ab initio scheme to compute and converge the \textit{e}-ph relaxation times (RTs) and electron mobility in polar materials. We apply our approach to GaAs, where using the Boltzmann equation with state-dependent RTs, we compute mobilities in excellent agreement with experiment at 250$-$500~K. The $e$-ph RTs and the phonon contributions to intravalley and intervalley $e$-ph scattering are also…
We have calculated (ab initio) and measured (by spin-echo techniques) the anharmonic self-energy of phonons at the X-point of the Brillouin zone for isotopically pure germanium. The real part agrees with former, less accurate, high temperature data obtained by inelastic neutron scattering on natural germanium. For the imaginary part our results provide evidence that transverse acoustic phonons at the X-point are very long lived at low temperatures, i.e. their probability of decay approaches zero, as a consequence of an unusual decay mechanism allowed by energy conservation.
Ultrafast laser measurements probe the non-equilibrium dynamics of excited electrons in metals with increasing temporal resolution. Electronic structure calculations can provide a detailed microscopic understanding of hot electron dynamics, but a parameter-free description of pump-probe measurements has not yet been possible, despite intensive research, because of the phenomenological treatment of electron-phonon interactions. We present ab initio predictions of the electron-temperature dependent heat capacities and electron-phonon coupling coefficients of plasmonic metals. We find substantial…
Band structure, Fermi surface, and phonon dispersions of noncentrosymmetric B20-type RhGe are calculated ab initio for the first time and their evolution with increasing pressure is investigated. We consider in detail symmetry-conditioned features of the band structure, as well as pressure-induced changes in the Fermi surface topology, which are expected to affect the thermopower of RhGe. We also report on special calculations of electric field gradients on the Rh and Ge nuclei and compare these results with a very recent 111 Cd-TDPAC study of B20-RhGe.
In the spin 1/2 antiferromagnetic Ca2CuO3 the optical excitation along 1D a Cu-O chain showed the enrichment of forbidden peaks that could not be explained by the group theory. We present the cluster-model ab initio study of these optical phonons based on the Hartree-Fock SCF calculation with the 3-21G basic set. The obtained results showed very good agreement with the observed data. The Cu-O resonances generally showed the lower shifts in Ca2CuO3 than in pure CuO and were primarily composed of the vibrations of the oxygen in static host lattice whereas the Cu movements happened only in the co…
Recently, phonons with chirality (chiral phonons) have attracted significant attention. Chiral phonons exhibit angular and pseudo-angular momenta. In circularly polarized Raman spectroscopy, the peak split of the $Γ_3$ mode is detectable along the principal axis of the chiral crystal in the backscattering configuration. In addition, peak splitting occurs when the pseudo-angular momenta of the incident and scattered circularly polarized light are reversed. Until now, chiral phonons in binary crystals have been observed, whereas those in unary crystals have not been observed. Here, we observe ch…
We study the mutual coupling of spin fluctuations and lattice vibrations in paramagnetic CrN by combining atomistic spin dynamics and ab initio molecular dynamics. The two degrees of freedom are dynamically coupled leading to non-adiabatic effects. Those effects suppress the phonon life times at low temperature compared to an adiabatic approach. The here identified dynamic coupling provides an explanation for the experimentally observed unexpected temperature dependence of the thermal conductivity of magnetic semiconductors above the magnetic ordering temperature.
Spin-phonon coupling is the main drive of spin relaxation and decoherence in solid-state semiconductors at finite temperature. Controlling this interaction is a central problem for many disciplines, ranging from magnetic resonance to quantum technologies. Spin relaxation theories have been developed for almost a century but often employ a phenomenological description of phonons and their coupling to spin, resulting in a non-predictive tool and hindering our detailed understanding of spin dynamics. Here we combine fourth-order time-local quantum master equations with advanced electronic structu…
We present a combined treatment of the non-equilibrium dynamics and transport of electrons and phonons by carrying out \textit{ab initio} calculations of the fully coupled electron and phonon Boltzmann transport equations. We find that the presence of mutual drag between the two carriers causes the thermopower to be enhanced and dominated by the transport of phonons, rather than electrons as in the traditional semiconductor picture. Drag also strongly boosts the intrinsic electron mobility, thermal conductivity and the Lorenz number. Impurity scattering is seen to suppress the drag-enhancement…
This paper gives a short overview of the calculation of thermal properties of materials from first principles, using the Quasi-Harmonic Approximation (QHA). We first introduce some of the thermal properties of interest and describe how they can be calculated in the framework of the QHA; then we briefly recall Density-Functional Perturbation Theory as a tool for calculating phonons from first principles, and present some codes that implement it; finally we review recent applications of first-principle QHA.
Lattice thermal conductivity ($κ_{lat}$) of MgSiO$_3$ postperovskite (MgPPv) under the Earth's lower mantle high pressure-temperature conditions is studied using the phonon quasiparticle approach by combing \textit{ab initio} molecular dynamics and lattice dynamics simulations. Phonon lifetimes are extracted from the phonon quasiparticle calculations, and the phonon group velocities are computed from the anharmonic phonon dispersions, which in principle capture full anharmonicity. It is found that throughout the lowermost mantle, including the D" region, $κ_{lat}$ of MgPPv is ~25% larger than …
In recent years, palladium has proven to be a crucial component for devices ranging from nanotube field effect transistors to advanced hydrogen storage devices. In this work, I examine the phonon dispersion of fcc Pd using first principle calculations based on density functional perturbation theory. While several groups in the past have studied the acoustic properties of palladium, this is the first study to reproduce the phonon dispersion and associated anomaly with high accuracy and no adjustable parameters. In particular, I focus on the Kohn anomaly in the [110] direction.
We have used ab-initio density functional theory technique to understand the phase transitions and structural changes in various high temperature/pressure phases of LiAlO2. The electronic band structure as well as phonon spectra are calculated for various phases as a function of pressure. The phonon entropy used for the calculations of Gibbs free energy is found to play an important role in the phase stability and phase transitions among various phases. A sudden increase in the polyhedral bond lengths (Li/Al-O) signifies the change from the tetrahedral to octahedral geometry at high-pressure p…
We report first principles calculations of the phonon dispersions of PbTe both for its observed structure and under compression. At the experimental lattice parameter we find a near instability of the optic branch at the zone center, in accord with experimental observations.This hardens quickly towards the zone boundary. There is also a very strong volume dependence of this mode, which is rapidly driven away from an instability by compression. These results are discussed inrelation to the thermal conductivity of the material.
The monolayer of black phosphorous, or phosphorene, has recently emerged as a new 2D semiconductor with intriguing highly anisotropic transport properties. Existing calculations of its intrinsic phonon-limited electronic transport properties so far rely on the deformation potential approximation, which is in general not directly applicable to anisotropic materials since the deformation along one specific direction can scatter electrons traveling in all directions. We perform a first-principles calculation of the electron-phonon interaction in phosphorene based on density functional perturbatio…
We investigate the spin-nonconserving relaxation channel of excitons by their couplings with phonons in two-dimensional transition metal dichalcogenides using $\textit{ab initio}$ approaches. Combining $\text{GW}$-Bethe-Salpeter equation method and density functional perturbation theory, we calculate the electron-phonon and exciton-phonon coupling matrix elements for the spin-flip scattering in monolayer WSe$_{\text{2}}$, and further analyze the microscopic mechanisms influencing these scattering strengths. We find that phonons could produce effective in-plane magnetic fields which flip spin o…
We present an $\textit{ab initio}$ study of the thermodynamic properties of cubic CaSiO$_3$ perovskite (CaPv) over the pressure and temperature range of the Earth's lower mantle. We compute the anharmonic phonon dispersions throughout the Brillouin zone by utilizing the phonon quasiparticle approach, which characterizes the intrinsic temperature dependence of phonon frequencies and, in principle, captures full anharmonicity. Such temperature-dependent phonon dispersions are used to calculate $\textit{ab initio}$ free energy in the thermodynamic limit ($N \rightarrow \infty$) within the framewo…
We report first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. We analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. For a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two leads, the low-lying modes of the vibration are found to be most important. As a function of bias voltage, the …
The relation between ab initio molecular dynamics formalism and the electron-phonon interaction formalism [P.B. Allen and V. Heine, J. Phys. C 9, 2305 (1976)] is explored. The fundamental quantity obtained in the AIMD formalism - total energy for any configuration - is also obtained from the formalism (ES-DWF) that incorporates the role of Debye-Waller Factor in electronic structure calculations. The two formalisms are exactly equivalent and represent the direct and perturbation theory approaches to determine total energy. This equivalence allows either formalism to be used depending on the re…
We develop an ab initio formalism for dipolar electron-phonon interactions (EPI) in two-dimensional (2D) materials. Unlike purely longitudinal Fröhlich model, we show that the out-of-plane dipoles also contribute to the long-wavelength non-analytical behavior of EPI. And the 2D dipolar EPI plays an important role not only in the typical polar material MoS$_2$, but also in graphane and fluorinated graphene. By incorporating this formalism into Wannier-Fourier interpolation, we enable accurate EPI calculations for 2D materials and subsequent intrinsic carrier mobility prediction. The results sho…
While the thermoelectric figure of merit zT above 300K has seen significant improvement recently, the progress at lower temperatures has been slow, mainly limited by the relatively low Seebeck coefficient and high thermal conductivity. Here we report, for the first time, success in first-principles computation of the phonon drag effect - a coupling phenomenon between electrons and non-equilibrium phonons - in heavily doped region and its optimization to enhance the Seebeck coefficient while reducing the phonon thermal conductivity by nanostructuring. Our simulation quantitatively identifies th…
The lattice thermal conductivity and thermal transport properties of 2D $α$-selenene are investigated based on the first-principles calculations. The isotropic in-plane thermal conductivity is as low as 3.04 W m$^{-1}$ K$^{-1}$ at room temperature, even abnormally lower than $α$-tellurene which processes analogous configuration and lower Debye temperature. We find this abnormal phenomenon reasonably stems from the larger anharmonicity of the acoustic phonon branch. Moreover, the phonon spectra, elastic properties, and related thermal properties are also exhibited. Acoustic phonons contribute m…
Ba2Ti2Fe2As4O is a self-doped superconductor exhibiting a Tc ~ 21.5 K and containing, distinctively with respect to other Fe-based superconductors, not only [Fe2As2] layers but also conducting [Ti2O] sheets. This compound exhibits a transition at T* ~ 125 K which has tentatively been assigned in the literature to a possible density-wave order. However, the nature of this density wave (whether it is a charge- or spin-induced) is still under debate. Magnetism in Ba2Ti2Fe2As4O has never been experimentally confirmed, which raises the question whether this superconductor might be non-magnetic or e…
The phonon spectra of calcium, strontium, barium, radium, cadmium, zinc, magnesium, germanium, tin, and lead titanates with the perovskite structure are calculated from first principles within the density functional theory. By analyzing the unstable modes in the phonon spectra, the possible lattice distortions are determined and the energies of the corresponding phases are calculated. From analyzing the phonon spectra, force constants, and eigenvectors of TO phonons, a conclusion is drawn on the origin of the ferroelectricity in considered crystals. It is shown that the main factors determinin…
We present an ab initio approach for the calculation of phonon self-energies and their fluctuation diagnostics, which allows us to identify the electronic processes behind phonon anomalies. Application to the transition-metal-dichalcogenide monolayer 1H-TaS$_2$ reveals that coupling between the longitudinal-acoustic phonons and the electrons from an isolated low-energy metallic band is entirely responsible for phonon anomalies such as the mode softening and associated charge-density waves observed in this material. Our analysis allows us to distinguish between different mode-softening mechanis…
The calculations of thermal conductivity requires to know anharmonic properties of the crystal. For this purpose a non-perturbative anharmonic theory is applied, which do not make use of the potential energy expansion over atomic displacements, but instead, runs ab initio calculations of Hellmann-Feynman forces for atomic patterns of atoms with specific displacements to rebuild the anharmonic phonon frequencies, and group velocities. see [K.Parlinski, Phys.Rev. B 98, 054305 (2018),] The Green-Kubo equation for the thermal conductivity needs to know the above quantities and the phonon relaxatio…
Nonradiative carrier recombination at semiconductor deep centers is of great importance to both fundamental physics and device engineering. In this letter, we provide a revised analysis of K. Huang's original nonradiative multi-phonon (NMP) theory with ab initio calculations. First, we identify at first-principle level that Huang's concise formula gives the same results as the matrix based formula, and Huang's high temperature formula provides an analytical expression for the coupling constant in Marcus theory. Secondly, the anharmonic effects are corrected by taking into account local phonon …
We formulate an ab initio downfolding scheme for electron-phonon coupled systems. In this scheme, we calculate partially renormalized phonon frequencies and electron-phonon coupling, which include the screening effects of high-energy electrons, to construct a realistic Hamiltonian consisting of low-energy electron and phonon degrees of freedom. We show that our scheme, which we call constrained density-functional perturbation theory (cDFPT), can be implemented by slightly modifying the conventional DFPT, which is one of the standard methods to calculate phonon properties from first principles.…
We report a computational theoretical investigation of electron spin-flip scattering induced by the electron-phonon interaction in the transition-metal ferromagnets bcc Fe, fcc Co and fcc Ni. The Elliott-Yafet electron-phonon spin-flip scattering is computed from first-principles, employing a generalized spin-flip Eliashberg function as well as ab initio computed phonon dispersions. Aiming at investigating the amount of electron-phonon mediated demagnetization in femtosecond laser-excited ferromagnets, the formalism is extended to treat laser-created thermalized as well as nonequilibrium, nont…
Ab initio calculations and a direct method have been applied to derive the phonon dispersion curves and phonon density of states for the TiC crystal. The results are compared and found to be in a good agreement with the experimental neutron scattering data. The force constants have been determined from the Hellmann-Feynman forces induced by atomic displacements in the 2x2x2 supercell. The calculated phonon density of states suggests that vibrations of Ti atoms form acoustic branches, whereas the motion of C atoms is confined to optic branches. The elastic constants have been found using the de…
Establishing the structure-property relationship for grain boundaries (GBs) is critical for developing next generation functional materials, but has been severely hampered due to its extremely large configurational space. Atomistic simulations with low computational cost and high predictive power are strongly desirable, but the conventional simulations using empirical interatomic potentials and density functional theory suffer from the lack of predictive power and high computational cost, respectively. A machine learning interatomic potential (MLIP) recently emerged but often requires an exten…
Near-forward Raman scattering combined with ab initio phonon and bond length calculations is used to study the phonon-polariton transverse optical modes (with mixed electrical and mechanical character) of the II-VI ZnSeS mixed crystal under pressure. The goal of the study is to determine the pressure dependence of the poorly resolved percolation-type Zn-S Raman doublet of the three oscillator [1(Zn-Se),2(Zn-S)] ZnSe68S32 mixed crystal, which exhibits a phase transition at approximately the same pressure as its two end compounds (~14 GPa, zincblende-to-rocksalt), as determined by high-pressure …
We propose an electron-phonon parameterization which reliably reproduces the geometry and harmonic frequencies of a real system. With respect to standard electron-phonon models, it adds a "double-counting" correction, which takes into account the lattice deformation as the system is dressed by low-energy electron-phonon processes. We show the importance of this correction by studying potassium-doped picene (K$_3$Picene), recently claimed to be a superconductor with a $T_c$ of up to 18 K. The Hamiltonian parameters are derived from ab-initio density functional theory, and the lattice model is s…
The phonon dispersion curves of cubic BaTiO_3 have been computed within a first-principles approach and the results compared to the experimental data. The curves obtained are very similar to those reported for KNbO_3 by Yu and Krakauer [Phys. Rev. Lett. 74, 4067 (1995)]. They reveal that correlated atomic displacements along <100> chains are at the origin of the ferroelectric instability. A simplified model illustrates that spontaneous collective displacements will occur when a dozen of aligned atoms are coupled. The longitudinal interatomic force constant between nearest neighbour Ti and O at…
We present a new interpretation of measured Raman frequencies of a high-pressure structure of Silicon which was assigned previously to the beta-tin phase. Our results show that the beta-tin->Imma->sh phase transitions have been already indicated in this experiment which was performed before the discovery of the Imma phase. We have calculated phonon-dispersion curves for the beta-tin, Imma, and sh phases of silicon using the plane-wave pseudopotential approach to the density-functional theory and the density-functional perturbation theory within the local density approximation. With the new ass…
The four A1-TO Gamma phonon frequencies in lithium tantalate are calculated in the frozen-phonon approach from first principles using the full-potential linearized augmented plane wave method. A good agreement with the experimental data available is found for all modes; reliable displacement pattern of different modes becomes available from the calculated eigenvectors. The Raman spectra recorded for A1 modes in LiNbO3 exhibit a counter-intuitive softening of the A1-TO3 mode frequency with respect to that measured in LiTaO3. We explain this behaviour by a comparatively harder oxygen rotation in…
The first order standard perturbation theory combined with ab initio projector augmented wave operator challenges the realization of the standard Sternheimer equation with linear computational efficiency. This efficiency motivates us to describe the electron-phonon interaction in two-dimensional (2D) black phosphorous monolayer using generalized density functional perturbation theory (DFPT) with Boltzmann transport theory (BTE). Subsequently, linear response phonon dynamic behaviour in terms of conductivities, seebeck coefficients and transport properties are focused for its thermoelectric app…
We report inelastic neutron scattering measurements of phonon spectra in the parent superconductor iron-tuned chalcogenide Fe$_{1+x}$Te, for two different x contents (x $\leq$ 0.11), using neutron time-of-flight technique. Thermal neutron spectroscopy allowed to collect the low-temperature Stokes spectra over an extended Q-range, at 2, 40 and 120K - hence covering both the magnetic monoclinic and the paramagnetic tetragonal phases. Whereas cold-neutrons allowed to measure high-resolution anti-Stokes spectra at 140, 220 and 300K, thus covering the tetragonal phase. Our results evidence a spin-p…
Raman spectra obtained by the inelastic scattering of light by crystalline solids contain contributions from first-order vibrational processes (e.g. the emission or absorption of one phonon, a quantum of vibration) as well as higher-order processes with at least two phonons being involved. At second order, coupling with the entire phonon spectrum induces a response that may strongly depend on the excitation energy, and reflects complex processes more difficult to interpret. In particular, excitons (i.e. bound electron-hole pairs) may enhance the absorption and emission of light, and couple str…
We report the pressure and temperature dependence of the phonon density-of-states in superconducting Ca0.6Na0.4Fe2As2 (Tc=21 K) and the parent compound CaFe2As2, using inelastic neutron scattering. We observe no significant change in the phonon spectrum for Ca0.6Na0.4Fe2As2 at 295 K up to pressures of 5 kbar. The phonon spectrum for CaFe2As2 shows softening of the low-energy modes by about 1 meV when decreasing the temperature from 300 K to 180 K. There is no appreciable change in the phonon density of states across the structural and anti-ferromagnetic phase transition at 172 K. These results…
We formulate a first-principle scheme for structural optimization at finite temperature ($T$) based on the self-consistent phonon (SCP) theory, which accurately takes into account the effect of strong phonon anharmonicity. The $T$-dependence of the shape of the unit cell and internal atomic configuration is determined by minimizing the variational free energy in the SCP theory. At each optimization step, the interatomic force constants in the new structure are calculated without running additional electronic structure calculations, which makes the method dramatically efficient. We demonstrate …
In this paper we investigate from first principles the effect of the electron-phonon interaction in two paradigmatic nanostructures: trans-polyacetylene and polyethylene. We found that the strong electron-phonon interaction leads to the appearance of complex structures in the frequency dependent electronic self-energy. Those structures rule out any quasi-particle picture, and make the adiabatic and static approximations commonly used in the well-established Heine Allen Cardona (HAC) approach inadequate. We propose, instead, a fully ab-initio dynamical formulation of the problem within the Many…
The carrier dynamics in bulk Silicon, a paradigmatic indirect gap semiconductor, is studied by using the Baym-Kadanoff equations. Both the electron--electron(e-e) and electron--phonon(e-p) self--energies are calculated fully ab-initio by using a semi-static GW approximation in the e-e case and a Fan self-energy in the e-p case. By using the generalized Baym-Kadanoff ansatz the two-time evolution is replaced by the only dynamics on the macroscopic time axis. The enormous numerical difficulties connected with a real-time simulation of realistic systems is overcame by using a completed collision …
Comment on 2501.17230 and 2502.00103 "Phonon-mediated electron attraction in SrTiO3 via the generalized Frohlich and deformation potential mechanisms" and "Theory of ab initio downfolding with arbitrary range electron-phonon coupling"
We propose a fast method for high-throughput screening of potential superconducting materials. The method is based on calculating metallic screening of zone-center phonon modes, which provides an accurate estimate for the electron-phonon coupling strength. This method is complementary to the recently proposed Rigid Muffin Tin (RMT) method, which amounts to integrating the electron-phonon coupling over the entire Brillouin zone (as opposed to the zone center), but in a relatively inferior approximation. We illustrate the use of this method by applying it to MgB$_\text{2}$, where the high-temper…
\textit{Ab initio} calculations of electron-phonon interactions including the polar Fröhlich coupling have advanced considerably in recent years. The Fröhlich electron-phonon matrix element is by now well understood in the case of bulk three-dimensional (3D) materials. In the case of two-dimensional (2D) materials, the standard procedure to include Fröhlich coupling is to employ Coulomb truncation, so as to eliminate artificial interactions between periodic images of the 2D layer. While these techniques are well established, the transition of the Fröhlich coupling from three to two dimensions …
We report ab initio calculations of the electronic band structure, the corresponding optical spectra, and the phonon dispersion relations of trigonal alpha-HgS (cinnabar). The calculated dielectric functions are compared with unpublished optical measurements by Zallen and coworkers. The phonon dispersion relations are used to calculate the temperature and isotopic mass dependence of the specific heat which has been compared with experimental data obtained on samples with the natural isotope abundances of the elements Hg and S (natural minerals and vapor phase grown samples) and on samples prep…
