Theoretical Studies of the Selfassembly of Dilithiumphthalocyanine

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Theoretical Studies of the Self-assembly of
Dilithiumphthalocyanine

• Yingchun Zhang

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Outline

• Introduction
• Computational details
• ab initio done by Paula and Larry
• Molecular dynamics simulation
• MD results
• Conclusions
• Future work

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Introduction

• Metal phthalocyanine
• intense absorption of light in UV region
• overlap of the molecular orbitals between
  adjacent molecules
• very stable to chemical or thermal
  treatments
• polymorphism
• eg lithium phthalocyanine

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1) Different forms show different properties,
such as conductivity, magnetism, oxygen
sensitivity 2) Only x-form has a. the
presence of channels in which the dioxygen
molecules can migrate b. a strong overlap
between consecutive LiPc molecules in a stack
c. a very efficient spin diffusion
H.Yanagi, A.Manivannan, Thin Solid Films, 393
(2001) 28-33 J.J. Andre, M. Brinkmann, Synthetic
Metals 90 (1997) 211-216
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• Di-lithium phthalocyanine (Li2Pc) has been
  proposed for use as a solid electrolyte in
  lithium-ion batteries
• self-assembly ability in solid state
• lithium ion conducting channels
• single-ion transport characteristic of
  lithium ions
• The true structure of Li2Pc is still not very
  clear

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Structure of Li2Pc optimized with Density
Functional Theory
Data from Paula Alonso
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Structure of (Li2Pc)2 optimized with Hatree Fock
Theory
Data from Paula Alonso
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B3LYP/6-31G(d)
B3LYP/6-31G(d)
Data from Larry Scanlon
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Optimized energies (in Hartrees) and binding
energies (in Kcal/mol) for Li2Pc and (Li2Pc)2
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MD Simulations

• 8-molecule unit cell with atomic charge
  distribution 1
• 64-molecule unit cell with atomic charge
  distribution 1
• 64-molecule unit cell with atomic charge
  distribution 2

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MD1 8-molecule Unit Cell
1. Initial configuration
a19.5 ?, b19.5 ?, c13.2 ? Layer distance
3.45 ?
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2. Atomic charge distribution
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• 3. Simulation force field
• a. intramolecular terms
• bond potential
• valence angle potential
• dihedral angle potential

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b. 12-6 Lennard-Jones (LJ) potential c. long
range Coulombic potential Ewald Sum
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4. Simulation details the microcanonical
ensembles (NVE) simulation time 1200 ps
equilibration time 300 ps timestep 0.001 ps
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• 4. Three unit cell structure after simulation

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MD2 64-molecule Unit Cell
Initial configuration

• a39.0 ?, b39.0 ?, c26.4 ?
• T273K,300K,373K, and 473K

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Lithium Ions Conducting Channel

L.G. Scanlon, L.R. Lucente, W.A. Feld, G. Sandi,
D.J. Campo, A.E. Turner, C.S. Johnson, R.A.
Marsh, Proceedings - Electrochemical Society
(2001), 2000-36(Interfaces, Phenomena, and
Nanostructures in Lithium Batteries), 326-338
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Ion Conducting Channel at 300K without Addition
of External Electric Fleld
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Intermolecular Distance between Li Atoms from two
Adjacent Layers Obtained after MD
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Negative Electrostatic Potential Contours for
Li2Pc
P. R. Alonso, Project Report
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Side View of Ion Conducting Channel at Different
Temperature without Addition of External EF
300K
273K
473K
373K
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Top View of Ion Conducting Channel at Different
Temperature without Addition of External EF
300K
273K
373K
473K
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A closer look at the SAXS data of Li2PC at
several temperatures
This peak becomes a broad shoulder at 198 C.
This peak disappears at 198 C.
Data from Dr. Giselle Sandí, Argonne National
Laboratory
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Pair Radial Distribution Functions
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Atomic Structure Factors
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Velocity Autocorrelation Functions of Lithium
Atoms
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Diffusion Coefficient

• mean squared displacement (MSD)
• velocity antocorrelation function (VAF)

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Diffusion Coefficient of Li Ions
Unit cm2/s
V. Kuppa, E. Manias, Chem. Mater., 2002, 14,
2171-2175
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Temperature Dependence of Li Diffusion
Coefficient
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MD3 64-molecule Unit Cell
Atomic charge distribution
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Top View of Ion Conducting Channel at Different
Atomic Charge Distribution at 300K without
Addition of External EF
MD3
MD2
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Side View of Ion Conducting Channel at Different
Atomic Charge Distribution at 300K without
Addition of External EF
MD3
MD2
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Pair Radial Distribution Functions
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Atomic Structure Factors
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Velocity Autocorrelation Functions and Diffusion
Coefficient of Li Ions
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Conclusions

• An optimized Force Field for molecular dynamics
  calculations was obtained that reproduces the
  desired planar structure of Li2Pc crystalline
  arrangement.
• Both ab initio calculation and molecular dynamic
  simulation agree to show an optimized shifted
  structure for the stacking of two Li2Pc
  molecules.
• MD shows that a lithium ion channel could be
  realized in the simulated structure that can be
  identified as the responsible for ionic
  conduction.
• The self-diffusion coefficient from our
  simulation confirms our lithium ion transport
  mechanism, which is different from PEO. Li2Pc has
  the expected advantage of the single-ion
  transport characteristics for use as electrolyte
  in lithium-ion batteries.

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Future Works

• To get the total structure factor I(Q) or the
  x-ray from simulation and compared to experiment
  data
• To study the temperature dependence for MD3
  series
• To study EF dependence for MD2 and MD3 series
• With additional Li ions to the unit cell