Neutral self-defects in a silica model: A first-principles study

Martin‐Samos, Layla; Limoge, Yves; Crocombette, Jean-Paul; Roma, Guido; Richard, Nicolas; Anglada, Eduardo; Artacho, Emilio

doi:10.1103/physrevb.71.014116

Cited by 59 publications

(63 citation statements)

References 42 publications

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“…Boureau et al 30 discussed the thermodynamical lower bound of formation energy of β-cristobalite is 7.3 eV/defect and ab initio studies showed the formation energy is about 5 ∼ 9 eV/defect. 23,31,32 These values support the idea that the strain energy of 2m ring may not be a considerable barrier of generating this configuration in silica if one compares to the oxygen defects.…”

Section: Amorphous Structuresupporting

confidence: 59%

“…We considered initial temperatures up to 7,000 K to randomize the initial geometry. 23 We found that 5,000 K is sufficient to randomize the crystalline structure and remove any memory of the original state. Previous Car-Parrinello molecular dynamics simulations used atomic coordinates generated by empirical potential simulations and set the initial temperature at 3,500 K. 8 Our experience is that defects existing in the initial structure, cannot be removed by annealing even at this relatively high temperature.…”

Section: Computational Detailsmentioning

confidence: 89%

“…We note that our annealing rate, 2.5 × 10 14 K/s, is significantly slower than the previous ab initio simulations ( Various annealing schedules have been applied to previous simulations. 8,11,13,23 As a starting point, both crystalline and random configurations of atoms can be used. We used β-cristobalite as a starting point and set our initial temperature to be 5,000 K. β-cristobalite is a high temperature form of crystalline silica that can be constructed by considering a diamond crystal of silicon and placing oxygen atoms at the bond sites.…”

Section: Computational Detailsmentioning

confidence: 99%

“…8,23 To understand the origin of these differences, we performed a variety of different preparations for our simulations, i.e., we examined cells containing 8, 32, and 64 unit of SiO 2 with cooling rates ranging from 2.5 × 10 14 to 10 15 K/s. Among them, only the simulation for the 8 units of SiO 2 with a cooling rate of 2.5 × 10 14 K/s did not result in a 2m ring configuration.…”

Section: Amorphous Structurementioning

confidence: 99%

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Simulating liquid and amorphous silicon dioxide using real-space pseudopotentials

2012

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We present ab initio molecular dynamics simulations of liquid and amorphous silicon dioxide. The interatomic forces in our simulations are calculated using real-space pseudopotentials, which were constructed using density-functional theory. Our simulations are carried out using BornOppenheimer molecular dynamics, i.e., the electronic structure problem is solved by performing fully self-consistent calculations for each time step. Using a subspace filtering iteration technique, we avoid solving the Kohn-Sham eigenvalue with "standard" diagonalization methods. We consider systems with up to 192 atoms (64 SiO2 units) in a periodic supercell for simulations over 20 ps. The liquid and amorphous ensembles are formed by thermally quenching random configurations of silicon and oxygen atoms. We compare our liquid and amorphous simulations with previously performed Car-Parrinello molecular dynamic simulations and with experiment. In particular, we examine the possible formation of two-fold rings, which were not observed in previous simulations using quantum forces. We attribute this difference to a "biased" initial configuration, which inhibits the formation of two-fold rings. We also compare the structural properties of our simulated amorphous systems with neutron diffraction measurements and find good agreement.

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Section: Amorphous Structuresupporting

confidence: 59%

Section: Computational Detailsmentioning

confidence: 89%

Section: Computational Detailsmentioning

confidence: 99%

Section: Amorphous Structurementioning

confidence: 99%

See 2 more Smart Citations

Simulating liquid and amorphous silicon dioxide using real-space pseudopotentials

2012

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“…59 The glass model for amorphous SiO 2 , in the following named a-SiO 2 , was generated using classical molecular-dynamics simulations of quenching from a melt, as described in Ref. 60. The crystalline and amorphous QDs of 32 Si atoms after the ionic relaxation are represented in Fig.…”

Section: Sio 2 Matrices and Siqdsmentioning

confidence: 99%

Silicon quantum dots embedded in a SiO2matrix: From structural study to carrier transport properties

et al. 2013

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We study the details of electronic transport related to the atomistic structure of silicon quantum dots embedded in a silicon dioxide matrix using ab initio calculations of the density of states. Several structural and composition features of quantum dots (QDs), such as diameter and amorphization level, are studied and correlated with transport under transfer Hamiltonian formalism. The current is strongly dependent on the QD density of states and on the conduction gap, both dependent on the dot diameter. In particular, as size increases, the available states inside the QD increase, while the QD band gap decreases due to relaxation of quantum confinement. Both effects contribute to increasing the current with the dot size. Besides, valence band offset between the band edges of the QD and the silica, and conduction band offset in a minor grade, increases with the QD diameter up to the theoretical value corresponding to planar heterostructures, thus decreasing the tunneling transmission probability and hence the total current. We discuss the influence of these parameters on electron and hole transport, evidencing a correlation between the electron (hole) barrier value and the electron (hole) current, and obtaining a general enhancement of the electron (hole) transport for larger (smaller) QD. Finally, we show that crystalline and amorphous structures exhibit enhanced probability of hole and electron current, respectively.

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Electronic and Optical Properties of Silicon Nanocrystals

Bulutay

Ossicini

2010

Silicon Nanocrystals

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Several strategies have been researched over the last few years for light generation and amplification in silicon. One of the most promising one is based on silicon nanocrystals (Si NCs) with the aim of taking advantage of the reduced dimensionality of the nanocrystalline phase (1-5 nm in size) where quantum confinement, band folding, and surface effects play a crucial role [1,2]. Indeed, it has been found that the Si NC bandgap increases with decrease in size and a photoluminescence (PL) external efficiency in excess of 23% is obtained [3]. Si NC-based LED with high efficiency have been obtained by using Si NC active layers [4] and achieving separate injection of electrons and holes [5]. Moreover, optical gain under optical pumping has been already demonstrated in a large variety of experimental conditions [6][7][8][9][10][11].After the initial impulse given by the pioneering work of Canham on photoluminescence from porous Si [12], nanostructured silicon has received extensive attention. This activity is mainly centered on the possibility of getting relevant optoelectronic properties from nanocrystalline Si. The huge efforts made toward matter manipulation at the nanometer scale have been motivated by the fact that desirable properties can be generated by just changing the system dimension and shape. Investigation of phenomena such as the Stokes shift (difference between absorption and emission energies), the PL emission energy versus nanocrystals size, the doping properties, the radiative lifetimes, the nonlinear optical properties, the quantum-confined Stark effect (QCSE), and so on can give a fundamental contribution to the understanding of how the optical response of such systems can be tuned. A considerable amount of work has been done on excited Si NCs [2, 13-23], but a clear understanding of some aspects is still lacking. The question of surface effects, in particular oxidation, has been addressed in the last few years. Both theoretical calculations and experimental observations have been applied to investigate the possible active role of the interface on the optoelectronic properties of Si NCs. Different models have been proposed: Baierle et al. [24] have considered the role of the surface geometry distortion of small hydrogenated Si clusters in the excited state.

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Neutral self-defects in a silica model: A first-principles study

Cited by 59 publications

References 42 publications

Simulating liquid and amorphous silicon dioxide using real-space pseudopotentials

Simulating liquid and amorphous silicon dioxide using real-space pseudopotentials

Silicon quantum dots embedded in a SiO2matrix: From structural study to carrier transport properties

Electronic and Optical Properties of Silicon Nanocrystals

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