Construction and Application of Extended Ionic Models'

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Construction and Application of Extended Ionic
Models.

• Mark Wilson

CECAM 17.10.05
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Introduction.

• Develop simple ionic models.
• Allows long time- and length-scales.
• Move from responsive to predictive mode.

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Background.

• Ionic materials.

• strong environmental dependence.
• many-body effects significant.

• Predictive models require

• transferable
• physically-transparent
• computationally-tractable.

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Outline.

• Extended ionic models.
• Obtaining potential parameters.

• well-directed ab initio
• force-fitting.

• Example simulations

• filling carbon nanotubes
• oxides (Li2O).

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Extended Ionic Models.

• Start from the pair potential

• Extend as required.

• polarizable-ion model (PIM).

- induced moments.

• anisotropic-ion model (AIM)

- ions change in size and shape.
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Obtaining Parameters.

• Electronic structure calcs.

• HF, MP2, DFT

• Well-directed - derive specific parameters.
• Force-fitting - derive all together.
• Establish physically transparent relations.

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Obtaining Parameters.

• Electronic structure calcs.

• HF, MP2, DFT

Well-directed
Force-fitting
Specific parameters
All parameters together

• Establish physically transparent relations.

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Example polarizabilities.
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Example polarizabilities.
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Induced Dipoles.
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Induced Dipoles.
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Dipolar distortions Cation identity change.
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Quadrupolar distortion.
Dipolar distortions at high pressure.
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Force-fitting.

• Obtain parameters together.
• Density-functional calcs.

• forces fi.
• cell stresses h.
• multipole moments mi,qi.

• Retain physical meaning.

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An oxide - Li2O.

• super-ionic conductor.
• oxides difficult.
• full AIM required.

- force-fitting used.

• phonons
• Cp(T).

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Dynamics.
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An oxide - Li2O.

• super-ionic conductor.
• oxides difficult.
• full AIM required.

- force-fitting used.

• phonons
• Cp(T).

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Dynamics.
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Li2O Static properties
A2C44/(C11-C12) D(C12-C44)
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Experimental Observation.

• Interpreted w.r.t wurtzite (bulk crystal).

Sloan et al, JACS, 124, 2116, 2002.
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Inorganic nanotubes
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Phase diagram
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Filling Carbon Nanotubes
Sloan et al, Chem. Phys. Lett., 329,
61,2000 Meyer et al, Science, 289, 1324, 2000.
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Filling Carbon Nanotubes - why?

• Unique low-dimensional environment.

• Potential applications

• nanowires
• nanomoulds (templates)
• catalysis.

• Ionic materials well-suited.

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Filling Carbon Nanotubes - how?

• Simple model.

• pair-potential polarization
• Lennard-Jones ion-carbon
• carbon tube held rigid.

• Observe direct filling.
• Energy minimisations - Phase diagrams.

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Filling with KI.

• rocksalt (B1, 6-coordinate) bulk.
• explains expt. HRTEM. (responsive)
• predicts a filling mechanism.
• explains why crystals form.
• predicts new morphologies. (predictive)

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Filling Mechanism.
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Filling with KI.
- twisted crystals.
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Why does the crystal form?
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Why do twisted crystals form?
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twisted crystal
Predicted HRTEM
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Inorganic nanotubes
Blende
Rocksalt
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Inorganic nanotubes
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Inorganic nanotubes
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INT morphologies.
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INT morphologies.
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INT morphologies.
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INT morphologies.
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Experimental Observation.

• Interpreted w.r.t wurtzite (bulk crystal).
• Equivalent to a (2,2).

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Applied pressure.
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Applied pressure.
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Chiral Information Transfer ?
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LaCl3 Insertion.

• Effect of change in stoichiometry ?
• Experiment ? non-space-filling.

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screengrab_linettrace_lacl3_18_3_p2_11
For comparison my modelling from bulk LaI3
LaI3_my_model_comparison2
LaI3_my_model_comparison
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An oxide - Al2O3.

• intermediate ? Al.
• complex T,p morphology.
• pressure marker Cr3.

- force-fitting used.

• study pressure transitions

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ab initio calculations and experiments
corundum stable up to 100 GPa
Rh2O3(II), stable up to 220 GPa (?)
orthorhombic perovskite, high pressure phase
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Al2O3 U-V curves of high pressure phases(static
and dynamic) from MD simulation
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corundum
Rh2O3(II) structure
orthorhombic perovskite
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Rh2O3-(II) ?corundum transformationtime
evolution of cell angles
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Comparison to X-ray diffraction pattern
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Summary.

• Construct extended ionic models.
• Parameters from electronic structure calcs.
• Allows long time- and length-scales.

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Thanks to .

• Professor Paul Madden
• Dr. Sandro Jahn
• Dr. Steffi Friedrichs

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Who does what ?

• Dominik Daisenberger.

• amorphous Si
• Si clathrates.
• Experiments (!)

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Who does what ?

• Bevan Sharma

• Potential model development
• Intermediate-range order.
• Crystal phase transitions.

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ZnCl2
GeSe2
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Who does what ?

• Clare Bishop

• Phase diagrams of models systems
• Potential model development.
• Filling carbon nanotubes.

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Who does what ?

• Numaan Ahmed

• Models for longer length-scales.
• Adapting force-fitting technologies.
• Polymers and glasses.

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Who does what ?

• Hitesh Bhalla

• Strontium chloride.
• Effect of homopolar bonds.