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

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

Introduction to Nanotechnology Agenda Introduction to Molecular Nanotechnology Design and modeling of molecular machines Modeling Techniques Sufficiency of Current Modeling Methods Molecular Compilers Conclusion February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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? February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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) February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 February 15, 2019 Introduction to Nanotechnology

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 http://www.zyvex.com/nanotech/compChemLinks.html Potential Energy for modeling molecular machine http://www.zyvex.com/nanotech/nano4/brennerAbstract.html Chemical Reactions Mechanisms http://www.zyvex.com/nanotech/CDAarticle.html#makingdiamond Computational Nanotechnology http://www.zyvex.com/nanotech/compNano.html February 15, 2019 Introduction to Nanotechnology