1. Computational Nanotechnology
By: Dr. Ralph C.Merkle
Presented by:
Roshan P.Harjani

2. Introduction to Nanotechnology
About the Author
B.A., Computer Science, U.C. Berkeley
M.S., Computer Science, U.C. Berkeley
Ph.D., Electrical Engineering, Stanford University
Scientist at Xerox PARC
Vice President, Technology Assessment, Foresight Institute
Current research interest, Molecular Nanotechnology
February 15, 2019
Introduction to Nanotechnology

3. Introduction to Nanotechnology
Agenda
Introduction to Molecular Nanotechnology
Design and modeling of molecular machines
Modeling Techniques
Sufficiency of Current Modeling Methods
Molecular Compilers
Conclusion
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Introduction to Nanotechnology

4. Introduction History of computation
“Universal Computer”
Dates back to 19th century
“Universal Constructor”
More recent
Well understood by von Neumann in the 1940's
“Assembler”
Recognized by Drexler
Analogous to von Neumann's Universal Constructor
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Introduction to Nanotechnology

5. Basic Design of Drexler's Assembler
A molecular computer
One or more molecular positioning devices
Robotic arms
A well defined set of chemical reactions
Takes place at the tip of the arm
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Introduction to Nanotechnology

6. Claims of Computational Nanotechnology
Fabricate molecular machines with atomic precision
Fabricate a wide range of molecular structures
Reduce the time frame for developing
Fabricate devices with decreasing costs
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Introduction to Nanotechnology

7. High payoffs arise some Questions
What???
What such systems will look like?
How???
How will they work?
How will we be building them?
If???
If its feasible or not?
Will???
Will the current understanding of chemistry and physics be sufficient?
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Introduction to Nanotechnology

8. Computational Nanotechnology
Design and Modeling of molecular machines
Molecular machines specified in atomic detail
Modeled using the tools of computational chemistry
Two modeling techniques of particular utility
Molecular Mechanics
Ab Initio Methods
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Introduction to Nanotechnology

9. Molecular Mechanics Introduction
Computational modeling of the positions of the nuclei of individual atoms
Current packages on
PC - can handle systems with thousands of atoms
Supercomputers - can handle systems with hundreds of thousands of atoms or more
Concept
The individual nuclei are usually treated as point masses
Potential Energy (E), as a function of the distance between the nuclei
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Introduction to Nanotechnology

10. Example: The H2 molecule
Involves 2 nuclei
E is a simple function of the inter-nuclear distance r
Function E(r) takes into account
Inter-nuclear repulsion
Interactions between the electrons and the nuclei
Two hydrogen nuclei will adopt a position that minimizes E(r)
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Introduction to Nanotechnology

11. Introduction to Nanotechnology
The H2 molecule…
As, r  larger
Potential Energy of the system increases
Nuclei experience a restoring force that returns them to their original distance
As, r  smaller
Two nuclei are pushed closer together
Restoring force pushes them farther apart
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Introduction to Nanotechnology

12. Introduction to Nanotechnology
Summary
If we know the positions r1, r2, .... rN of N nuclei
E(r1, r2, .... rN) gives the potential energy of the system
Knowing the potential energy as a function of the nuclear positions
Determine the forces acting on the individual nuclei
Compute the evolution of their position over time
Potential energy E is a Newtonian concept
Particular values of E at particular points are determined by Schrodinger's equation
Many atomically precise stable structures can be modeled with an accuracy adequate to determine the behavior of molecular machines
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Introduction to Nanotechnology

13. Example: A Molecular bearing
This style of design has been called "Molecular Bridge Building"
Ripping apart bonds
Considering the stability
Class of bearings
Members of this class perform the desired function
The Computational tools that are capable of creating and modeling most of the members of a broad class of devices
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Introduction to Nanotechnology

14. Introduction to Nanotechnology
Ab Initio Methods
Problem with “Molecular Mechanics”
Do not provide sufficient accuracy to deal with chemical transitions
Impose severe constraints on the number of atoms that can be modeled
Provide an accuracy sufficient to analyze the chemical reactions
Analyze the addition or removal of atoms from a specific site on a work piece
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Introduction to Nanotechnology

15. Sufficiency of Current Modeling Methods
It is quite possible to adequately model the behavior of molecular machines that satisfy two constraints
They are built from parts that are sufficiently stable
The synthesis of the parts is done by using positionally controlled reactions
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Introduction to Nanotechnology

16. Can we model Drexler's Assembler?
Fundamental purpose of an assembler is to position atoms
Molecular mechanics
Second fundamental requirement is the ability to make and break bonds at specific sites
Higher order Ab Initio Methods
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Introduction to Nanotechnology

17. Introduction to Nanotechnology
Drexler's Assembler…
The Molecular Computer
Possible to model electronic behavior with some degree of accuracy
Molecular mechanical computation is sufficient for the molecular computer
Molecular mechanical proposals are better understood than Electronic designs
Using our current approaches and methods
Drexler's assembler can be modeled
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Introduction to Nanotechnology

18. Introduction to Nanotechnology
Molecular Compilers
Tools to specify such Molecular Machines
Input
High level description of an object
Output
Atomic coordinates, atom types and bonding structure of the object
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Introduction to Nanotechnology

19. A simple Molecular Compiler
Already been written at PARC
The Specifications set consists of
“scale 0.9”
shrink the size of the structure by 10% compared with the normal size
“tube…”
tells the program to produce a tubular structure
“grid…”
specifies that a grid is to be laid down on the surface
“delete…”
specifies that the point at coordinates “…” is to be deleted
“change O_3 to S_3…”
causes all oxygen atoms to be changed to sulfur
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Introduction to Nanotechnology

20. Introduction to Nanotechnology
Conclusion
Derive detailed description of the behavior of proposed systems
Substantially reduce the development time for complex molecular machines
It is possible to debate how long it will be before we achieve a robust molecular manufacturing capability.
We'll get there sooner if we develop and make intelligent use of molecular design tools and computational models
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Introduction to Nanotechnology

21. Topics of Interest / References
A simple Molecular Compiler written at PARC
The C source code is available at URL
ftp://ftp.parc.xerox.com/pub/nano/tube.c
Links to internet Computational Chemistry resources
Potential Energy for modeling molecular machine
Chemical Reactions Mechanisms
Computational Nanotechnology
February 15, 2019
Introduction to Nanotechnology