Electron Emission from Diamondoids: A Diffusion Quantum Monte Carlo Study

Drummond, Neil; Williamson, Andrew; Needs, R. J.; Galli, Giulia

doi:10.1103/physrevlett.95.096801

Cited by 170 publications

(177 citation statements)

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“…[1][2][3][4] Such systems are promising candidates for tuning of optical properties, [5][6][7] with a variety of applications ranging from molecular building blocks for optoelectronics to biocompatible, photostable biomarkers. [8][9][10][11][12][13][14][15] In particular, the observation of photoluminescence (PL) in reduced-dimensional semiconductor systems, which otherwise exhibit an indirect band gap, like Si and C (diamond), opens possibilities to tailor their optical properties and to interface with already existing technologies. [2][3][4] However, despite numerous studies, [2][3][4]16,17 the fundamental photophysical processes in such systems still are not fully understood.…”

Section: Introductionmentioning

confidence: 99%

Size and shape dependent photoluminescence and excited state decay rates of diamondoids

Richter

Wolter

Zimmermann

et al. 2014

Phys. Chem. Chem. Phys.

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We present photoluminescence spectra and excited state decay rates of a series of diamondoids, which represent molecular structural analogues to hydrogen-passivated bulk diamond. Specific isomers of the five smallest diamondoids (adamantane-pentamantane) have been brought into the gas phase and irradiated with synchrotron radiation. All investigated compounds show intrinsic photoluminescence in the ultraviolet spectral region. The emission spectra exhibit pronounced vibrational fine structure which is analyzed using quantum chemical calculations. We show that the geometrical relaxation of the first excited state of adamantane, exhibiting Rydberg character, leads to the loss of T d symmetry. The luminescence of adamantane is attributed to a transition from the delocalized first excited state into different vibrational modes of the electronic ground state. Similar geometrical changes of the excited state structure have also been identified in the other investigated diamondoids. The excited state decay rates show a clear dependence on the size of the diamondoid, but are independent of the particle geometry, further indicating a loss of particle symmetry upon electronic excitation.

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Section: Introductionmentioning

confidence: 99%

Size and shape dependent photoluminescence and excited state decay rates of diamondoids

Richter

Wolter

Zimmermann

et al. 2014

Phys. Chem. Chem. Phys.

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“…Our DMC-predicted OGs for adamantane and diamantane are about 0.26 (8) eV smaller than in the previous DMC work. 3 The DMC calculations in Ref. 3 were more primitive than those reported here in various regards: they used a single, fixed time step of 0.02 a.u., the excited-state wave function was constructed by replacing the HOMO with the LUMO for downspin electrons in a single-determinant wave function, and DFT pseudopotentials were used to represent the ionic cores.…”

Section: Methodsmentioning

confidence: 99%

“…For comparison, previous DMC results 3 along with available experimental data are also given. Two different experimental methods have been used to measure the OGs of small diamondoids.…”

Section: A Optical Gapmentioning

confidence: 99%

“…A great deal of theoretical effort using different many-body techniques has been devoted to calculating the absorption gaps of diamondoids, which are often referred to as optical gaps (OGs). [3][4][5][6][7] However, the measured energy emitted from these materials and the corresponding emission gap (EG) is also of great technological importance. To our knowledge, no previous theoretical study has investigated the Stokes shift-the difference of the absorption and EGs-exhibited by these novel materials.…”

Section: Introductionmentioning

confidence: 99%

“…For this reason, diamondoids have been the subject of a large number of experimental and theoretical studies in recent years. [1][2][3] Advances in theoretical condensed-matter physics and first-principles computational methods in the last two decades have made it possible to develop a comprehensive understanding of the electronic and optical properties of a wide range of materials. A great deal of theoretical effort using different many-body techniques has been devoted to calculating the absorption gaps of diamondoids, which are often referred to as optical gaps (OGs).…”

Section: Introductionmentioning

confidence: 99%

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Comparison of quantum Monte Carlo with time-dependent and static density-functional theory calculations of diamondoid excitation energies and Stokes shifts

2011

Self Cite

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We compute the absorption and emission energies and hence Stokes shifts of small diamondoids as a function of size using different theoretical approaches, including density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations. The absorption spectra of these molecules are also investigated by time-dependent DFT and compared with experiment. We analyze the structural distortion and formation of a self-trapped exciton in the excited state, and we study the effects of these on the Stokes shift as a function of size. Compared to recent experiments, QMC overestimates the excitation energies by about 0.8(1) eV on average. Benefiting from a cancellation of errors, the optical gaps obtained in DFT calculations with the B3LYP functional are in better agreement with experiment. It is also shown that time-dependent B3LYP calculations can reproduce most of the features found in the experimental spectra. According to our calculations, the structures of diamondoids in the excited state show a distortion which is hardly noticeable compared to that found for methane. As the number of diamond cages is increased, the distortion mechanism abruptly changes character. We have shown that the Stokes shift is size dependent and decreases with the number of diamond cages. If we neglect orbital symmetry effects on the optical excitations, the rate of decrease in the Stokes shift is, on average, 0.1 eV per cage for small diamondoids.

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Diamondoid Molecules

Mansoori¹

2007

Advances in Chemical Physics

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Diamondoids have been of great interest in recent years due to their role in nanotechnology, drug-delivery and medicine. In this review paper we introduce at first the cage nature of diamondoid molecules (polymantanes, adamantologues), the variety of their crystalline lattice structures, the nature of their structural isomers, their stereoisomers, and their other molecular specificities are presented. The carbon-carbon framework of diamondoids constitutes the fundamental repeating unit in the diamond lattice structure. It is demonstrated that diamondoids are very stable compounds.The unique physicochemical properties of diamondoids due to their exceptional atomic arrangements including their melting points, molar enthalpies, molar entropies, molar heat capacities, vapor pressures and other phase transitions and solubilities data are reported and analyzed.The Lewis acid-catalyzed rearrangement of hydrocarbons to synthesize lower diamondoids is presented and its limitations for the synthesis of higher diamondoids are discussed.The natural occurrence of diamondoids in petroleum fluids and how they come to be present in such fluids is introduced. Field experiences of phase transitions and depositions as well as techniques for separation, detection and measurement of diamondoids from petroleum fluids is presented and discussed..It is demonstrated that due to their six or more linking groups diamondoids have found major applications as templates and as molecular building blocks in polymers synthesis, nanotechnology, drug delivery, drug targeting, DNA directed assembly, DNA-amino acid nanostructure formation and in host-guest chemistry. ________________________________________ (*) E-Mail: mansoori@uic.edu. 2 Molecular Structure of DiamondoidsDiamondoid molecules are cage-like, ultra-stable, saturated hydrocarbons. These molecules are ringed compounds, which have a diamond-like structure consisting of a number of six-member carbon rings fused together (see Figure 1). More explicitly, they consist of repeating units of ten carbon atoms forming a tetra-cyclic cage system [1-3]. They are called "diamondoid" because their carbon-carbon framework constitutes the fundamental repeating unit in the diamond lattice structure. This structure was first determined in 1913 by Bragg and Bragg [4] using X-ray diffraction analysis.The first and simplest member of the diamondoids group, adamantane, is a tricyclic saturated hydrocarbon (tricyclo[3.3.1.1]decane). Adamantane is followed by its polymantane homologues (adamantologues): diamantane, tria-, tetra-, penta-and hexamantane. Figure 1, illustrate the smaller diamondoid molecules, with the general chemical formula C 4n+6 H 4n+12 : adamantane (C 10 H 16 ), diamantane (C 14 H 20 ), and triamantane (C 18 H 24 ),.. These lower adamantologues, each has only one isomer.Depending on the spatial arrangement of the adamantane units, higher polymantanes (n≥4) can have several isomers and non-isomeric equivalents. There are three possible tetramantanes all of which are isomeric. They are depicte...

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Electron Emission from Diamondoids: A Diffusion Quantum Monte Carlo Study

Cited by 170 publications

References 27 publications

Size and shape dependent photoluminescence and excited state decay rates of diamondoids

Size and shape dependent photoluminescence and excited state decay rates of diamondoids

Comparison of quantum Monte Carlo with time-dependent and static density-functional theory calculations of diamondoid excitation energies and Stokes shifts

Diamondoid Molecules

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