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![Page 1: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/1.jpg)
First-principles molecular dynamics studies of liquid and glasses
Carlo MassobrioInstitut de Physique et Chimie des MatériauxStrasbourg (France) (CNRS-Univ. L. Pasteur)
Old Strasbourg: "Petite France"
Short and intermediate rangeorder structural propertiesin disordered network-formingmaterials: AX2, An X(1-n)
A=Ge, Si , X=Se
Current Challenges in Liquid and Glasses ScienceCosener’s House, Abingdon, United Kingdom, 10-12/1/2007
![Page 2: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/2.jpg)
First-principles molecular dynamics studies of liquid and glasses
Carlo MassobrioInstitut de Physique et Chimie des MatériauxStrasbourg (France) (CNRS-Univ. L. Pasteur)
Liquid GeSe2 at 1100 K
Short and intermediate rangeorder structural propertiesin disordered network-formingmaterials: AX2, An X(1-n)
A=Ge, Si , X=Se
Current Challenges in Liquid and Glasses ScienceCosener’s House, Abingdon, United Kingdom, 10-12/1/2007
![Page 3: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/3.jpg)
Our model: essential featuresFirst principles molecular dynamicsDensity functional theory: best with GGA…!! (case of GeSe2)Periodic cell, Plane waves basis setsNorm conserving pseudopotentials
kmin < 0.4 Å-1 kFSDP 1 Å-1
(intermediate range order scales)
Length of equilibrium trajectories : Liquids : up to 100 ps (significant sampling ensured by diffusion) Glasses : Quench of uncorrelated liquid configurations (LC) followed by structural relaxationEx: GeSe2: for each LC, 22 ps down to T=600K and 22 ps at T=300 K
Typical size of the periodic boxes: L=15-20 Å (N=120,144)
Computer code: norm-conserving version of ultra-soft FPMD written by A. Pasquarello (Lausanne) (PRL 69, 1982 (1992), PRB 47, 10142 (1993))
How do we deal with space and time limitations..?
![Page 4: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/4.jpg)
Two issues of methodology:
1) Role of the generalized gradient approximation (GGA) within density functional theory (case of liquid GeSe2)(CM, Alfredo Pasquarello, Roberto Car, JACS 121, 2943 (1999))
2) System size and periodicity: are they compatible with IRO..?(CM, Alfredo Pasquarello, Roberto Car, PRB 64, 144205 (2001))
![Page 5: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/5.jpg)
Correlation between structure and bonding properties:role of the GGA in DFT (case of liquid GeSe2)
Ionic character of bonding enhanced:GGA brings the FSDP together with the predominant occurrence ofa tetrahedral order.
LDA
GGA
![Page 6: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/6.jpg)
Two issues of methodology:
1) Role of the generalized gradient approximation (GGA) within density functional theory (case of liquid GeSe2)(CM, Alfredo Pasquarello, Roberto Car, JACS 121, 2943 (1999))
2) System size and periodicity: are they compatible with intermediate range order (IRO) distances...?
(CM, Alfredo Pasquarello, Roberto Car, PRB 64, 144205 (2001))
![Page 7: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/7.jpg)
Total S(k) for a given L= 15.7 Å
drkr
sinkr
αβ
Rc4παβ ][ 1(r)gr1S
2
ij
)(e R jβRiik
βααβ
NNS
Two ways are available to calculate the structure factors…
Real space (solid line)
Reciprocal space (dotted line):our approach
The FSDP becomes clearly discernible for Rc in between 6 and 10 Å
Extent of correlations responsible of the FSDP
![Page 8: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/8.jpg)
FSDPFSDP
I.T. Penfold and P.S. Salmon, PRL 67, 97(1991)
Scc/cge cse = 1+cgecse(Sgege-Sgese)
+cgecse(Ssese-Sgese)
Liquid GeSe2: a prototype case
FSDP in both total andScc structure factors
Scc/cgecse = SZZ
For point charges (classical MD): no FSDP in SCC
charge-charge structure factorezz
)rr(ik ji
vji,j
vi
Total S(k)
![Page 9: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/9.jpg)
Note: LDA (dotted line) inaccurate!!!
SNNStot
“…the distribution of the FSDP weigthsin the partials is different in theory andexperiments..” (PRB 64, 144205 (2001))
Reduced intensity of FSDP in SGeGe and Scc
![Page 10: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/10.jpg)
dGeGe (exp) = 2.33 0.03 Å
dGeGe = 2.7 0.1 ÅLiquid GeSe2
Theory 0.04 3.76 1.88 0.37Exp 0.25 3.5 1.75 0.23CON 0 4 2 0 RCN 2 2 1 1
CON chemically ordered networkRCN random covalent network
Ngege Ngese Nsege Nsese
Liquid GeSe2 is a highly defective tetrahedral network, withmiscoordinations and homopolar bonds
![Page 11: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/11.jpg)
![Page 12: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/12.jpg)
Amorphous GeSe2
High statistics required:about 500 ps (quench+relaxation)Results from a single quench
“true” (chain-like)homopolar Ge-Ge bondsare found
Liquid vs amorphous (dotted line)
CM and Alfredo Pasquarello, unpublished
![Page 13: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/13.jpg)
Understanding the origins of the FSDP in theconcentration-concentration structure factor Scc
Liquid (l) GeSe2
Two approaches: 1) Look for analogies and differences with other systems (SiO2, SiSe2, GeSe4)2) Exploit statistical mechanics on relevant configurations of l-GeSe2
![Page 14: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/14.jpg)
Amorphous SiSe2
Enhanced chemical order
nsisi nsise nsesi nsese
Theory 0.06 3.89 1.94 0.10CON 0 4 2 0RCN 2 2 1 1
Si(0) 26% 48% 30%
Si(1) 52% 46% 61%
Si(2) 22% 6 % 9%
Exp. CMD
Si(1)
Si(2)Si(0)
Massimo Celino and CM, PRL 64, 125502 (2003)
![Page 15: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/15.jpg)
Understanding the origins of the FSDP in theconcentration-concentration structure factor Scc
Liquid (l) GeSe2
Two approaches: 1) Look for analogies and differences with other systems (SiO2, SiSe2, GeSe4)2) Exploit statistical mechanics on relevant configurations of l-GeSe2
![Page 16: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/16.jpg)
How to calculate Scc and Szz structure factors
Scc= cacx[1+cacx((SAA-SAX)+(SXX-SAX))]
e)s()r(drdsS)sr(ik
ttzz
zi ionic charges (Ge= 4, Se =6)
)r()rr(z)r( eit ii
POINT-LIKE CHARGE (PLC) MODEL
S)cc(S ccba
PLCzz
1 ezz)rr(ik ji
vji,j
vi
i it )rr(z)r( vi
No FSDP in Szz
(charge neutralityon IRO scales)(CM and Alfredo PasquarelloPRB 68, 020201 (2003))
What is the behavior of Scc
for systems having in common the FSDPin the total S(k)..??
![Page 17: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/17.jpg)
Correlation between FSDP in Scc and chemical disorder
Case I: perfect chemical order: l-SiO2 (theory)
Case II: small deviations from chemical order: a-SiSe2 (theory)
Case III: large deviations from chemical order:l-GeSe2 (theory)
![Page 18: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/18.jpg)
Disordered networks: 3 classes of systems identified
Moderate chemical disorder (case II): Occurrence of different valence statesVariations of concentration induce FSDP in Scc
Ex: l-GeSe4, a-SiSe2, l-GeSe2 (exp)
Perfect network (case I, l-SiO2 ): charge neutrality does not require any local variation of the
concentration: FSDP absent in Scc
High chemical disorder (case III) :FSDP in the total S(k) but FSDP absent(or very small) in Scc
Ex: l-GeSe2 (theory)
Intensity of FSDP in Scc
Case I
Case II
Chemical disorder
Case III
Chemical disorder
(CM, Massimo Celino and Alfredo PasquarelloPRB 70, 174202 (2004))
![Page 19: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/19.jpg)
Understanding the origins of the FSDP in theconcentration-concentration structure factor Scc
Liquid (l) GeSe2
Two approaches: 1) Look for analogies and differences with other systems (SiO2, SiSe2, GeSe4)2) Exploit statistical mechanics on relevant configurations of l-GeSe2
![Page 20: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/20.jpg)
liquid GeSe2Idea: look at the time behavior
DFT underestimates the height of the FSDP in Scc
Average value
![Page 21: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/21.jpg)
Proposal:We select configurations belonging totwo sub-trajectories:« low » when FSDP in Scc lower than average« high » when FSDP in Scc higher than average
Intermediate range orderas expressed through the Ge-Ge structure factor: much better agreement for the trajectory « high »..!!!
![Page 22: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/22.jpg)
By using the samescheme, we comparethe two sets of Bhatia-Thorntonstructure factors
« low » « high »
Note : the NNs are very close: both sets yield very good total structure factors
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Comparing an extensive listof structural properties(coordination numbers, rings topology, g (r) )the results on the two trajectoriesare very close…
Where does the difference come from..?Number of Ge in two fourfold rings(chains of edge-sharing tetrahedra):Ge* units
The trajectory « high »has a higher numberof Ge* subunits
Warning: 1 and 2 form a Ge*, 2 and 3 do not…!!!
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Striking correlation between the number of Ge* subunitsand the height of the FSDP in Scc
Link with chemical disorder: number n of Ge and Ge* n-fold coordinated
n 1 2 3 4 5Ge 0.2 5.3 22.4 60.9 10.8Ge* 1.6 10.5 30.0 41.6 16.5
« Superatoms Ge* » aremore defective than Ge
CM and Alfredo Pasquarello, PRB 2007
![Page 25: First-principles molecular dynamics studies of liquid and glasses Carlo Massobrio Institut de Physique et Chimie des Matériaux Strasbourg (France) (CNRS-Univ.](https://reader035.fdocuments.in/reader035/viewer/2022062518/56649efd5503460f94c11819/html5/thumbnails/25.jpg)
Structural studies of disordered network-forming materials:quantitative AND predictive power of
first-principles molecular dynamics at short and intermediate range-order distances
Ge-Se based systems: challenging and stimulating for DFT approaches
Many thanks toIPCMSCNRSIDRIS (France), CINES (France) CSCS (Switzerland)Computer centers
Work in collaboration withAlfredo Pasquarello(early stages: Roberto Car)
on Si-Se systemsMassimo Celino