Metadynamical approach to the generation of amorphous structures: The case of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>a</mml:mi></mml:math>-Si:H

Biswas, Parthapratim; Atta‐Fynn, Raymond; Elliott, S. R.

doi:10.1103/physrevb.93.184202

Cited by 14 publications

(7 citation statements)

References 69 publications

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“…Alternatively, we can make use of assumptions about the anticipated geometric arrangements within the material to design empirical potentials, thus avoiding the computational expense of ab initio calculations 20,21 . These can be very effective for cases where we already understand the nature of the interactions within a material, although they still often require more sophisticated algorithms to produce the highest quality models 22,23 . For a-Si, one of the simplest and most successful approaches has been the Wooten Winer Weaire (WWW) algorithm, which generates four-fold coordinated random networks by combining bond-switch moves with relaxation against a classical potential 14,24,25 .…”

Section: Introductionmentioning

confidence: 99%

Structural simplicity as a restraint on the structure of amorphous silicon

et al. 2017

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Understanding the structural origins of the properties of amorphous materials remains one of the most important challenges in structural science. In this study we demonstrate that local 'structural simplicity', embodied by the degree to which atomic environments within a material are similar to each other, is powerful concept for rationalising the structure of canonical amorphous material amorphous silicon (a-Si). We show, by restraining a reverse Monte Carlo refinement against pair distribution function (PDF) data to be simpler, that the simplest model consistent with the PDF is a continuous random network (CRN). A further effect of producing a simple model of a-Si is the generation of a (pseudo)gap in the electronic density of states, suggesting that structural homogeneity drives electronic homogeneity. That this method produces models of a-Si that approach the state-of-the-art without the need for chemically specific restraints (beyond the assumption of homogeneity) suggests that simplicity-based refinement approaches may allow experiment-driven structural modelling techniques to be developed for the wide variety of amorphous semiconductors with strong local order. arXiv:1609.00668v3 [cond-mat.mtrl-sci]

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Section: Introductionmentioning

confidence: 99%

Structural simplicity as a restraint on the structure of amorphous silicon

et al. 2017

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“…[13][14][15][16][17] Moreover, non-bonded hydrogens (NBHs) or unbonded hydrogens, most likely H 2 molecules, also exist in the voids, 15,[17][18][19][20][21] and occupying T-like sites. [21][22][23] It is known that bonded hydrogen content (C BH ) [24][25][26][27][28] and film thickness (d) 29) are related to the optical band gap (E opt ). Considering the relationship between E opt and the internal stress, it has been suggested that the incorporated divacancies and nanovoids induced anisotropic volumetric compressive stress in the a-Si network, resulting in an enhancement in E opt .…”

Section: Introductionmentioning

confidence: 99%

Dense restructuring of amorphous silicon network induced by non-bonded hydrogen

Sekimoto¹,

Matsumoto²,

Terakawa³

2018

Jpn. J. Appl. Phys.

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We confirmed the presence of non-bonded hydrogens (NBHs) in hydrogenated amorphous silicon (a-Si:H) films, using a combination of multiple techniques (Rutherford backscattering spectrometry/hydrogen forward scattering, Fourier-transform infrared spectroscopy-attenuated total reflection, and thermal desorption spectrometry). The hydrogen effusion profile of an a-Si:H film with large amounts of NBHs was analyzed in detail. We report the effect of NBHs on band structure and electrical conductivity, and we present additional considerations for previous data on number density of silicon, optical bandgap, and vacancy size distribution [J. Non-Cryst. Solids 447, 207 (2016)]. The effect of NBHs on the a-Si network is explained by the "dense restructuring model".

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“…% H and an a-Si:D model with 12.2 at. % D. The models were generated using a recently developed metadynamical approach, 26 which is capable of producing high-quality networks of a-Si:H/D, 26 coupled with ab initio interactions. The CPMD simulations are based on the density-functional theory (DFT) of Kohn and Sham, 27,28 which employs norm-conserving pseudopotentials and plane-wave basis functions, as implemented within the NWCHEM code.…”

Section: Computational Methodologymentioning

confidence: 99%

First-principles simulations of vibrational decay and lifetimes ina-Si:H anda-Si:D

et al. 2017

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Phonon lifetime in materials is an important observable that conveys basic information about structure, dynamics and anharmonicity. Recent vibrational transient-grating measurements, using picosecond infrared pulses from free-electron lasers, have demonstrated that the vibrational-population decay rates of localized high-frequency stretching modes (HSMs) in hydrogenated and deuterated amorphous silicon (a-Si:H/D) increase with temperature and the vibrational energy redistributes among the bending modes of Si in a-Si:H/D. Motivated by this observation, we address the problem from first-principles density-functional calculations and study the time evolution of the vibrational-population decay in a-Si:H/D, the average decay times and the possible decay channels for the redistribution of vibrational energy. The average lifetimes of the localized HSMs in a-Si:H and a-Si:D are found to be approximately 51-92 ps and 50-78 ps, respectively, in the temperature range of 25-200 K, which are consistent with experimental data. A weak temperature dependence of the vibrational-population decay rates has been observed via a slight increase of the decay rates with temperature, which can be attributed to stimulated emission and increased anharmonic coupling between the normal modes at high temperature.

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Metadynamical approach to the generation of amorphous structures: The case ofa-Si:H

Cited by 14 publications

References 69 publications

Structural simplicity as a restraint on the structure of amorphous silicon

Structural simplicity as a restraint on the structure of amorphous silicon

Dense restructuring of amorphous silicon network induced by non-bonded hydrogen

First-principles simulations of vibrational decay and lifetimes ina-Si:H anda-Si:D

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