Structure of liquid<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ge</mml:mi></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Se</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi>−</mml:mi><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>at the stiffness threshold composition

Haye, M.J.; Massobrio, Carlo; Pasquarello, Alfredo; Vita, A. De; Leeuw, Simon de; Car, Roberto

doi:10.1103/physrevb.58.r14661

Cited by 27 publications

(44 citation statements)

References 24 publications

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“…The bond angle of this connection, $90°, is much smaller than, e.g., the Ge-Se-Ge bond angle in glassy GeSe 2 or the Se-Se-Se bond angle in glassy Se, and such a small bond angle would be very stressful. The existence of the small bond angle was also pointed out by a recent ab initio molecular dynamics simulation on liquid GeSe 4 [30]. This correlation may come from Ge(Se 1=2 ) 4 tetrahedra connected by a Se 2 short chain, i.e., Ge-Se-Se-Ge configuration.…”

Section: Discussionmentioning

confidence: 85%

Intermediate-range order in glassy GexSe1−x around the stiffness transition composition

Wang

Ohata

Hosokawa

et al. 2004

Journal of Non-Crystalline Solids

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Section: Discussionmentioning

confidence: 85%

Intermediate-range order in glassy GexSe1−x around the stiffness transition composition

Wang

Ohata

Hosokawa

et al. 2004

Journal of Non-Crystalline Solids

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“…The main peak in S CC (k) is due to correlations among nearest neighbors and occurs at a value of k ϳ2/r min , where r min ϭ3 Å corresponds to the first minimum in the pair distribution functions. 16 The FSDP at k ϳ1 Å Ϫ1 stems mostly from Ge-Ge correlations involving distances between 5 and 10 Å. The shape of the chargecharge structure factor S zz (k) is drastically different.…”

Section: ͑6͒mentioning

confidence: 99%

“…10,14 -16 We used the same technical ingredients as in previous work on l-GeSe 4 . 16 Since the charge density had not been recorded in the latter simulations, we carried out a new simulation at T ϭ1075 K, taking statistical averages over a time period of 10 ps. 11 We write the charge-charge structure factor S zz (k) as…”

mentioning

confidence: 99%

Absence of charge-charge correlations at intermediate-range distances in disordered network-forming materials

Massobrio

Pasquarello

2003

Phys. Rev. B

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Applying a first-principles scheme to liquid GeSe 4 , we show that the charge-charge structure factor does not present any feature at the location of the first sharp diffraction peak ͑FSDP͒, despite a clear FSDP in the concentration-concentration structure factor S CC (k). The origin of this effect is assigned in part to the finite extent of the electron density and in part to electron rearrangements. Our result provides evidence in favor of the postulate that, in binary network-forming systems, charge-charge correlations are absent on intermediaterange length scales. A FSDP in the S CC (k) then signals the occurrence of structural defects.The presence of a first sharp diffraction peak ͑FSDP͒ in the total structure factor of liquid and glasses is a signature of an intermediate-range order ͑IRO͒ established on distances well beyond nearest neighbors. 1-3 The FSDP can be related to specific structural correlations by considering the partial structure factors. 4,5 In particular, a FSDP in the Bhatia-Thornton concentration-concentration partial structure factor S CC (k),is indicative of fluctuations of concentration on distances typical of the IRO. S AA (k), S AX (k), and S XX (k) are the Faber-Ziman partial structure factors for a binary system made of A and X species of concentrations c A and c X , respectively. We note that the presence of a positive ͑negative͒ peak in S CC (k) corresponds to preferred correlations among atoms of the same ͑different͒ kind on length scales associated with the value of k. The absence of a peak reflects insensitivity to the chemical nature of the neighbors. On the basis of classical molecular-dynamics simulations, it was postulated that the absence of a FSDP in the structure factor S zz (k) is a general feature of any AX 2 disordered network, independently of the adopted theoretical scheme. 6,7 This statement appeared undermined by neutron-diffraction measurements which showed a FSDP in the structure factor S CC (k) of liquid GeSe 2 (l-GeSe 2 ). 8,9 In fact, under the assumption of pointlike ionic charges ͑as is the case in classical molecular dynamics͒, the structure factor S CC (k) becomes trivially proportional to the charge-charge structure factor S zz (k). However, for real systems the pointlike ionic model is only an approximation, and S CC (k) and S zz (k) are no longer necessarily equivalent. Hence, the postulation that charge-charge fluctuations are absent on intermediate-range distances might still have a profound meaning. The situation became even more intriguing when first-principles molecular-dynamics simulations of l-GeSe 2 , which properly account for charge transfer, also did not show any FSDP in the structure factor S CC (k), yet exhibiting excellent agreement for the total neutron structure factor over the entire k range. 10 In this work, we investigate the relation between chargecharge correlations and concentration-concentration correlations for a realistic system. We selected liquid GeSe 4 because previous simulations have shown that l-GeSe 4 presents a FSDP in t...

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“…25 This class is consistent with very moderate departures from chemical order, as confirmed by the structure of l-GeSe 4 and l-SiSe 2 obtained by simulation. 23,26,27 A network structure of class III has so far only been encountered in first-principles molecular dynamics simulations of l-GeSe 2 . 18 Like for class I, no feature appears at the FSDP location in the S CC ͑k͒.…”

Section: Introductionmentioning

confidence: 99%

Charge fluctuations and concentration fluctuations at intermediate-range distances in the disordered network-forming materialsSiO2,Si
Massobrio
¹
,
Celino
²
,
Pasquarello
³

2004
Phys. Rev. B
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We calculate the concentration-concentration partial structure factor S CC ͑k͒ and the charge-charge structure factor S zz ͑k͒ of liquid SiO 2 , amorphous SiSe 2 and liquid GeSe 2 using first-principles molecular dynamics. These systems are characterized by the occurrence of intermediate range order, as evidenced by a first sharp diffraction peak (FSDP) at low k values in the total neutron structure factor. We show that a FSDP in the concentration-concentration partial structure factor S CC ͑k͒ is generally associated with a small departure from chemical order. This feature tends to vanish either when sufficiently high levels of structural disorder set in, or, oppositely, when the chemical order is essentially perfect. For none of these networks, a FSDP is observed in the charge-charge structure factor S zz ͑k͒, i.e., fluctuations of charge do not occur over intermediate range distances. The constraint of charge neutrality is at the very origin of the appearance of fluctuations of concentration. These are observed when the atoms occur in configurations with different coordinations.

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Structure of liquidGexSe1−xat the stiffness threshold composition

Cited by 27 publications

References 24 publications

Intermediate-range order in glassy GexSe1−x around the stiffness transition composition

Intermediate-range order in glassy GexSe1−x around the stiffness transition composition

Absence of charge-charge correlations at intermediate-range distances in disordered network-forming materials

Charge fluctuations and concentration fluctuations at intermediate-range distances in the disordered network-forming materialsSiO2,Si
Massobrio
¹
,
Celino
²
,
Pasquarello
³

2004
Phys. Rev. B
Self Cite

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Structure of liquidGexSe1−xat the stiffness threshold composition

Cited by 27 publications

References 24 publications

Intermediate-range order in glassy GexSe1−x around the stiffness transition composition

Intermediate-range order in glassy GexSe1−x around the stiffness transition composition

Absence of charge-charge correlations at intermediate-range distances in disordered network-forming materials

Charge fluctuations and concentration fluctuations at intermediate-range distances in the disordered network-forming materialsSiO2,SiMassobrio1, Celino2, Pasquarello3 2004Phys. Rev. BSelf Cite

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Product

Resources

About

Charge fluctuations and concentration fluctuations at intermediate-range distances in the disordered network-forming materialsSiO2,Si
Massobrio
¹
,
Celino
²
,
Pasquarello
³

2004
Phys. Rev. B
Self Cite