Phonon spectrum of beryllium at 80K

Stedman, R.; Amilius, Z; Pauli, R.; Sundin, O

doi:10.1088/0305-4608/6/2/012

Cited by 68 publications

(41 citation statements)

References 25 publications

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“…The phonon dispersion relationship predicted using this method, Fig. 3, demonstrates reasonable agreement with the phonons measured using neutron scattering [20,21]. At 300 K the impact of anharmonic forces in beryllium is expected to be small [22].…”

Section: Beryllium Phonon Dossupporting

confidence: 67%

Thermal neutron scattering law calculations using ab initio molecular dynamics

Wormald

Hawari

2017

EPJ Web Conf.

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Abstract. In recent years, methods for the calculation of the thermal scattering law (i.e. S(α, β), where α and β are dimensionless momentum and energy transfer variables, respectively) were developed based on ab initio lattice dynamics (AILD) and/or classical molecular dynamics (CMD). While these methods are now mature and efficient, further advancement in the application of such atomistic techniques is possible using ab initio molecular dynamics (AIMD) methods. In this case, temperature effects are inherently included in the calculation, e.g. phonon density of states (DOS), while using ab initio force fields that eliminate the need for parameterized semi-empirical force fields. In this work, AIMD simulations were performed to predict the phonon spectra as a function of temperature for beryllium and graphite, which are representative nuclear reactor moderator and reflector materials. Subsequently, the calculated phonon spectra were utilized to predict S(α, β) using the LEAPR module of the NJOY code. The AIMD models of beryllium and graphite were 5 × 5 × 5 crystal unit cells (250 atoms and 500 atoms respectively). Electronic structure calculations for the prediction of Hellman-Feynman forces were performed using density functional theory with a GGA exchange correlation functional and corresponding core electron pseudopotentials. AIMD simulations of 1000-10,000 time-steps were performed with the canonical ensemble (NVT thermostat) for several temperatures between 300 K and 900 K. The phonon DOS were calculated as the power spectrum of the AIMD predicted velocity autocorrelation functions. The resulting AIMD phonon DOS and corresponding inelastic thermal neutron scattering cross sections at 300 K, where anharmonic effects are expected to be small, were found to be in reasonable agreement with the results generated using traditional AILD. This illustrated the validity of the AIMD approach. However, since the impact of the temperature on the phonon DOS (e.g. broadening of spectral peaks) was observed in AIMD analysis, this technique may be envisioned as the approach for deriving the needed atomistic data for thermal scattering law calculations under realistic temperature and structural conditions for a given material.

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Section: Beryllium Phonon Dossupporting

confidence: 67%

Thermal neutron scattering law calculations using ab initio molecular dynamics

Wormald

Hawari

2017

EPJ Web Conf.

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“…Let's start by comparing , to the bulk phonon DOS [42] in Figure 5. It is obvious that peaks #6-#9 are associated with the coupling of the surface states to the bulk phonons.…”

Section: Discussionmentioning

confidence: 99%

Electron-phonon coupling in a system with broken symmetry: Surface ofBe(0001)

Chien

et al. 2015

Phys. Rev. B

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The momentum-resolved Eliashberg function (ELF), , , for the Be(0001) zone-center surface state was extracted from the high-quality angle-resolved photoemission spectroscopy (ARPES) data at the Fermi energy in the Γ direction, displaying ten peaks. A comparison of the peaks in the ELF to the bulk phonon density of states (DOS) and the bulk and surface phonon dispersion allows for an identification of the origin of all but two of the peaks. The five high energy peaks (> 52 meV) are associated with the coupling of the surface state to bulk phonon modes. The peaks at 44.5 meV and at 49.0 meV have contributions from both the bulk and surface phonons. The most intense peak at 37.5 meV is evidently having contribution from EPC of the surface state to the surface Rayleigh phonon mode. Surprisingly, the two lowest energy modes, which must be associated with surface Rayleigh phonon, cannot be attributed to a high phonon DOS at the surface nor to any Fermi surface nesting. After detail analysis, the three lowest energy peaks are associated with momentum dependence in the EPC matrix, reflected in the phonon line-width changes. As a result of the broken symmetry at the surface, coupling of the initial surface state due to the presence of the surface phonons contributes ~48.5±12.5% of the spectral weight in the ELF and ~6 6.5±10.5% to the mass enhancement ( ).

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“…47͒ and are in good agreement with the experimental neutron diffraction data. 48 To obtain the spectral functions needed for the calculation of the imaginary part of the self-energy the summation over the phonon wave vectors q and phonon branches was performed by using the linear tetrahedron method 49 with more than 6000 tetrahedra in the IBZ because of rather significant variation of the electron-phonon matrix elements throughout the BZ. The Dirac delta functions in Eqs.…”

Section: A Electron-phonon Interactionmentioning

confidence: 99%

Role of electron-phonon interactions versus electron-electron interactions in the broadening mechanism of the electron and hole linewidths in bulk Be

et al. 2005

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We report on ab initio study of electron-phonon ͑e-ph͒ and electron-electron ͑e-e͒ interactions in bulk Be. The calculations show that the e-ph coupling parameter varies from 0.01 to 1.02 as a function of electron energy and momentum, = 0.21 at the Fermi level as averaged over momenta. The e-ph contribution ⌫ e-ph to the electrons and holes lifetime broadening also manifests clear dependence on the momentum and energy of an electron state. We demonstrate that the e-ph coupling matrix elements strongly affect the Eliashberg function especially for low phonon frequencies. By using the Debye model relation between ⌫ e-ph and the characteristic Debye frequency D is obtained in good agreement with the experimental one. The e-e contribution to the lifetime broadening is evaluated from the imaginary part of the electron self-energy computed within a GW approximation.

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Phonon spectrum of beryllium at 80K

Cited by 68 publications

References 25 publications

Thermal neutron scattering law calculations using ab initio molecular dynamics

Thermal neutron scattering law calculations using ab initio molecular dynamics

Electron-phonon coupling in a system with broken symmetry: Surface ofBe(0001)

Role of electron-phonon interactions versus electron-electron interactions in the broadening mechanism of the electron and hole linewidths in bulk Be

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