MoleculeMolecule Intermolecular Potentials on a Gold Surface

1
Molecule-Molecule Intermolecular Potentials on a
Gold Surface

• By Jacob Harvey, RPI
• In partner with Howard Mayne and Greg Bubnis

2
Introduction

• Molecules on gold surface pivot around center
  point
• Each atom on the rotor induces a potential on the
  atoms of the neighboring rotors

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Morse Potential

• Potential is calculated using the Morse Equation
• Parameters B tightness factor
• Re Optimal distance
• R actual distance
• D energy parameter

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Graph of Morse Potential Energy

• Two particle system with one being stationary
• Parameters D 10000
• Re .7
• B 5

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Quick Look at Parameters

• Larger B value tightens the well
• Smaller B value widens the well

B10 Re.7
B1 Re.7
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Quick Look at Parameters

• A larger Re value shifts the graph right
• A smaller Re value shifts the graph left

Re.2 B5
Re1.0 B5
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Two Rotor System

• Each rotor is allowed to spin on central point
  and is affected by other rotors
• Therefore each atom feels a potential from two
  other atoms
• What are the optimal orientations?
• What parameters lead to these orientations?

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Adjusting value of Re

• What happens when you adjust the value of Re?
• The parameter B is set equal to 5 and is held
  constant
• When 0ltRelt.8
• Optimal orientations exist when rotors exist at
  an angle of 0 or any multiple of 180

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Adjusting Value of Re

• When Regt.8
• Optimal orientations now exist when both rotors
  are at 90

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Adjusting Value of Re

• What about when Re .8, B5?
• Here the system appears to be in a transition
  state with many minimums

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Re .8

• Where are the optimal orientations for Re.8?
• They can be found using the process called
  Simulated Annealing

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Adjusting the Parameter of B

• The parameter B can also be adjusted to obtain
  various orientations. Re is set equal to .7 and
  is held constant.
• When Bgt1.5 the optimal orientation is 180

Bgt1.5
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Adjusting the Parameter B

• When Blt1.5 the optimal orientation is 90

Blt1.5
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B 1.5

• Again the system appears to be in transition

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B 1.5

• Using the same process as before the optimal
  orientations can be found

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Adjusting the length of Rotor

• Finally the last parameter to adjust is the
  length of the rotor
• Is it optimal to have a long rotor?
• Is it optimal to have a short rotor?

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Short Rotor

• What does the system look like for a short rotor?
• Parameters B5, Re.7, Rotor Length.25

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Long Rotor

• What does the system look like for a longer
  rotor?
• Parameters B5,Re.7,Rotor Length1.0

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Long or Short?

• The minima for longer rotors actually yield a
  lower energy
• It is more practical to have the rotors form a
  line
• Lower Energy More
  Practical

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Which Parameter Drives the System

• What happens when a B value that is favorable to
  a 180 orientation is used with a Re value that
  is favorable to a 90 orientation?

B5 Re1.0
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Big Picture

• How can this research be used?
• More Rotors
• Rotors can potentially be aligned to form
  pseudo nano-wires

Work by Greg Bubnis
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Organic Rotors

• What might a rotor look like?
• Molecule can potentially rotate in its position
  on a gold surface
• Potential created by the polar ends of the
  molecule

Fullerene compound synthesized by Miller group