Quantum nuclear dynamics in the photophysics of diamondoids

Patrick, Christopher E.; Giustino, Feliciano

doi:10.1038/ncomms3006

Cited by 104 publications

(142 citation statements)

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“…25,29,45 In a previous study, we have already shown that based on the calculation of vibrationally resolved FranckCondon spectra in the frame of the TDDFT method, which includes the structural displacements upon changing the electronic state, the experimental emission spectrum of adamantane can be accurately reproduced. 28 Here, we have further exploited this approach and have obtained a very good agreement of the calculated vibrationally resolved spectra with their measured high-resolution counterparts for a large class of higher diamondoids.…”

Section: Resultsmentioning

confidence: 99%

“…Size-and shape-selected neutral diamondoids in the gas phase are optimal model systems for theory, especially for the study of quantum confinement effects. [20][21][22][23][24][25] In particular, doped or surface-modified diamondoids [2][3][4][5][6] as well as diamondoid dimers or trimers are extremely attractive as nanoscale building blocks for applications. Another interesting feature is the photoluminescence of diamondoids.…”

Section: Introductionmentioning

confidence: 99%

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Laser-induced fluorescence of free diamondoid molecules

Richter

Röhr

Zimmermann

et al. 2015

Phys. Chem. Chem. Phys.

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aWe observe the fluorescence of pristine diamondoids in the gas phase, excited using narrow band ultraviolet laser light. The emission spectra show well-defined features, which can be attributed to transitions from the excited electronic state into different vibrational modes of the electronic ground state. We assign the normal modes responsible for the vibrational bands, and determine the geometry of the excited states. Calculations indicate that for large diamondoids, the spectral bands do not result from progressions of single modes, but rather from combination bands composed of a large number of Dv = 1 transitions. The vibrational modes determining the spectral envelope can mainly be assigned to wagging and twisting modes of the surface atoms. We conclude that our theoretical approach accurately describes the photophysics in diamondoids and possibly other hydrocarbons in general.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Laser-induced fluorescence of free diamondoid molecules

Richter

Röhr

Zimmermann

et al. 2015

Phys. Chem. Chem. Phys.

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“…For the determination of band gaps in the solid state, both electron-phonon coupling and thermal expansion are important [24][25][26]. Studying the effects of electron-phonon coupling on the band gaps of solids from first principles has only recently become possible [22,[27][28][29][30]. In this paper, we combine the first-principles calculation of anharmonicity, electron-phonon coupling and thermal expansion to study the vibrational corrections to the thermal band gap of solid He and hence determine an accurate value for the metalization pressure including the effects of temperature.…”

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confidence: 99%

“…This expectation value can be calculated by writing the operatorÔ(Q) within a principal axes representation like that for the energy [22], or nonperturbatively by sampling phase space according to the nuclear density [28,30]. The first method is approximate, but the description is in terms of individual phonons, permitting direct access to the underlying physical processes.…”

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confidence: 99%

Electron-Phonon Coupling and the Metallization of Solid Helium at Terapascal Pressures

et al. 2014

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Solid He is studied in the pressure and temperature ranges 1-40 TPa and 0-10,000 K using firstprinciples methods. Anharmonic vibrational properties are calculated within a self-consistent field framework, including the internal and free energies, density-pressure relation, stress tensor, thermal expansion, and the electron-phonon coupling renormalization of the electronic band gap. We find that an accurate description of electron-phonon coupling requires us to use a non-perturbative approach. The metalization pressure of 32.9 TPa at 0 K is larger than found previously. The vibrational effects are large; for example at P = 30 TPa the band gap is increased by 2.8 eV by electron-phonon coupling and a further 0.1 eV by thermal expansion compared to the static value. The implications of the calculated metalization pressure for the cooling of white dwarfs are discussed.PACS numbers: 63.20. Ry, 62.50.p Helium (He) is the second most abundant element in the Universe after hydrogen and one of the most important components of stellar bodies such as giant gaseous planets, main-sequence stars, and white dwarf (WD) stars. The large value of the first excitation energy of atomic He of 19.82 eV leads to a high metalization pressure for the solid phase, of the order of tens of terapascals. Calculations of the phase diagram of He [1,2] indicate that, in the terapascal pressure range, it remains solid up to temperatures of around 8, 000 K. He is therefore expected to be found in the solid state in the outer layers of cool WDs.The vast majority of the stars in the Universe become WDs in the final stages of their evolution, with the gravitational attraction towards the center being balanced by the electron degeneracy pressure of the high-density core. The lack of a continuous energy source means that WDs cool down until reaching thermodynamic equilibrium with their surroundings, eventually becoming black dwarfs. An understanding of the cooling process [3] is essential when calculating the ages of observed WDs, which are widely used within cosmochronology [4,5] to date stellar clusters and galaxies, and hence to provide bounds on the age of the Universe.The cores of WDs are largely isothermal due to the high thermal conductivity of degenerate electrons. Hence the cooling rate is mainly determined by the outer layers, which are composed of hydrogen, He, or a mixture of both. In this context the insulator-metal transition in solid He is central because energy transport from the degenerate core is dominated by electron transport through metallic He in the deeper layers, and by photon transport through insulating He in the outermost region [6].Recent work has focused on the study of the metalization pressure of He in the solid and fluid states [6][7][8][9][10][11]. In the solid state [6], static-lattice electronic structure calculations using both the diffusion Monte Carlo (DMC) many-body wave function technique [12,13] and the GW approximation of many-body perturbation theory [14] have shown that standard generalized gradient approx...

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“…Recent years have witnessed a surge of interest in ab initio calculations of EPIs, leading to new techniques and many innovative applications in the case of metals and non-polar semiconductors [1][2][3][4][5][6][7][8][9][10][11][12]. In contrast to this fast-paced progress, in the case of polar semiconductors and insulators the study of EPIs from first principles has not gone very far, owing to the prohibitive computational costs of EPI calculations for polar materials.…”

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confidence: 99%

Fröhlich Electron-Phonon Vertex from First Principles

2015

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We develop a method for calculating the electron-phonon vertex in polar semiconductors and insulators from first principles. The present formalism generalizes the Fröhlich vertex to the case of anisotropic materials and multiple phonon branches, and can be used either as a post-processing correction to standard electron-phonon calculations, or in conjunction with ab initio interpolation based on maximally localized Wannier functions. We demonstrate this formalism by investigating the electron-phonon interactions in anatase TiO2, and show that the polar vertex significantly reduces the electron lifetimes and enhances the anisotropy of the coupling. The present work enables ab initio calculations of carrier mobilities, lifetimes, mass enhancement, and pairing in polar materials.PACS numbers: 71.38.-k, 63.20.dk The electron-phonon interaction (EPI) is a cornerstone of condensed matter physics, and plays important roles in a diverse array of phenomena. Recent years have witnessed a surge of interest in ab initio calculations of EPIs, leading to new techniques and many innovative applications in the case of metals and non-polar semiconductors [1][2][3][4][5][6][7][8][9][10][11][12]. In contrast to this fast-paced progress, in the case of polar semiconductors and insulators the study of EPIs from first principles has not gone very far, owing to the prohibitive computational costs of EPI calculations for polar materials. For example, a fully ab initio calculation of the carrier mobility of a polar semiconductor has not been performed yet, while such calculations have recently been reported for non-polar semiconductors such as silicon [13] and graphene [14]. Given the fast-growing technological importance of polar semiconductors, from light-emitting devices to transparent electronics, solar cells and photocatalysts [15][16][17], developing accurate and efficient computational methods for studying EPIs in these systems is of primary importance.At variance with metals and non-polar semiconductors, in polar materials two or more atoms in the unit cell carry nonzero Born effective charge tensors [18]. As a consequence, the fluctuations of the ionic positions corresponding to longitudinal optical (LO) phonons at long wavelength generate macroscopic electric fields which can couple strongly to electrons and holes, leading to the so-called Fröhlich interaction [19]. Up to now this interaction has not been taken into account in ab initio calculations of EPIs; the two key obstacles towards a description of Fröhlich coupling from first principles are (i) the Fröhlich coupling was designed to describe simple isotropic systems with one LO phonon, and (ii) the electron-phonon vertex diverges for q → 0, where q is the phonon wavevector. The first obstacle relates to the fundamental question on how to define the Fröhlich coupling in the most general way. The second obstacle renders first-principles calculations extremely demanding, since a correct description of the singularity requires a very fine sampling of the Brillouin zone.In...

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Quantum nuclear dynamics in the photophysics of diamondoids

Cited by 104 publications

References 50 publications

Laser-induced fluorescence of free diamondoid molecules

Laser-induced fluorescence of free diamondoid molecules

Electron-Phonon Coupling and the Metallization of Solid Helium at Terapascal Pressures

Fröhlich Electron-Phonon Vertex from First Principles

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