Invalidity of Molecular Dynamics in Heat Transfer


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Invalidity of Molecular Dynamics in Heat Transfer

  • Thomas Prevenslik
  • QED Radiations
  • Discovery Bay, Hong Kong
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • 1

Introduction

  • Molecular Dynamics (MD) is commonly used to simulate heat transfer at the nanoscale in the belief:
  • Atomistic response using L-J potentials (ab initio) is more accurate than macroscopic finite element (FE) programs, e.g., ANSYS, COMSOL, etc.
  • In this talk, I argue:
  • FE gives equivalent heat transfer to MD, but both are invalid at the nanoscale by Quantum Mechanics (QM)
  • And ask the question:
  • How to make MD and FE at least consistent with QM?
  • 2
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012

MD and FE Restrictions

  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • 3

Validity

  • Historically, MD simulations of the bulk performed in submicron computation boxes under periodic boundary conditions (PBC) assume atoms have heat capacity
  • In the macroscopic bulk being simulated, all atoms do indeed have heat capacity
  • (Computation box taken from bulk for analysis)
  • MD is therefore valid for bulk PBC simulations
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • 4

Problem

  • Today, MD is not made for bulk simulations, but rather for the atomistic response of discrete nanostructures
  • Problem is MD programs based on SM assume the atom has heat capacity that I will show is the cause of the unphysical results
  • Conductivity in Thin films depends on thickness
  • Nanofluids violate mixing rules, etc
  • Why is this so?
  • 5
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • Heat Capacity of the Atom
  • 6
  • Nanostructures
  • kT 0.0258 eV
  • SM, MD and FE (kT > 0)
  • QM
  • (kT = 0)
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • In nanostructures, the atom has no heat capacity by QM

Conservation of Energy

  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • Lack of heat capacity by QM precludes EM energy conservation in discrete nanostructures by an increase in temperature, but how does conservation proceed?
  • Proposal
  • Absorbed EM energy is conserved by creating QED photons inside the nanostructure - by frequency up or down - conversion to the TIR resonance of the nanostructure.
  • QED = Quantum Electrodynamics
  • TIR = Total Internal Reflection
  • 7
  • QED photons create charge or emitted to surroundings

TIR Confinement

  • If the refractive index of nanostructure is greater than that of surroundings, the proposed QED photons are confined by TIR
  • ( Tyndall, 1870 )
  • NPs have high surface to volume ratio.
  • EM energy is absorbed almost totally in the NP surface.
  • The NP surface is the TIR wave function shape of QED photons.
  • QED photons are created upon EM energy absorption.
  • f = c/  = 2nD E = hf
  • 8
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012

QED Heat Transfer

  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • 9
  • QED Photons
  • Phonons
  • Charge
  • T = 0

MD - Discrete and PBC

  • Akimov, et al. “Molecular Dynamics of Surface-Moving Thermally Driven Nanocars,”
  • J. Chem. Theory Comput. 4, 652 (2008).
  • Sarkar et al., “Molecular dynamics simulation of effective thermal conductivity and study of enhance thermal transport in nanofluids,”
  • J. Appl. Phys, 102, 074302 (2007).
  • 10
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • Pretty Picture v QM Correctness?
  • MD for Discrete  kT = 0, But MD assumes kT > 0
  • Car distorts but does not move
  • Macroscopic analogy,
  • FE = MD
  • Classical Physics does not work
  • QM differs
  • No increase in car temperature
  • Charge is produced photoelectric effect
  • Car move by electrostatic interaction
  • MD for kT > 0 is valid for PBC because atoms in macroscopic nanofluid have kT > 0

Thermal Gradients

  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • 11
  • Q-W Hou, B-Y Cao and Z-Y Guo,“Thermal gradient induced actuation of double-walled carbon nanotubes,”, Nanotechnology, Vol. 20, 495503 , 2009
  • MD of Concentric CNTs
  • With MD, no CNT motion found.
  • Motion by adding a thermophoretic spring, but then no need for MD
  • By QM, more QED radiation is produced at hot than cold end
  • Charge is produced
  • Outer CNT moves under charge gradient to cold end.
  • Classical physics does not produce charge

Sputtering

  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
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  • Vienna U. Technology, www. Research Group Surface & Plasma Technology -.mht
  • MD 5 keV Ar atoms Impacting Cu
  • What can be done?
  • During MD solution, use Nose-Hoover thermostat to hold temperature constant as required by QM.
  • The QED radiation emitted is the net thermostat heat.
  • Input the QED radiation in FE programs to determine effect on the surroundings..

Conclusions

  • MD heat transfer based on SM assumes atoms have kT energy which is valid only for PBC
  • MD simulations of discrete nanostructures do not produce charge and are meaningless, except for pretty pictures.
  • MD and FE provide equivalent heat transfer simulations of discrete nanostructures, but both are invalid by QM and give unphysical results
  • QM negates SM, thermal conduction, Fourier Theory, and heat current at the nanoscale
  • Recommendation
  • Estimate the time-history of QED radiation and use in FE simulations to determine the effect on macroscopic surroundings. MD may not even be necessary
  • 13
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012

Expanding Unverse

  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • In 1929, Hubble measured the redshift of galaxy light that by the Doppler Effect showed the Universe is expanding.
  • But cosmic dust of submicron NPs permeate space and redshift galaxy light without Universe expansion
  • 14
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • 15
  • Redshift without Universe expansion
  • Based on classical physics, astronomers assume absorbed galaxy photon increases temperature of dust NPs
  • Redshift in Cosmic Dust
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
  • Referring to his calculation showing acccelerated Universe expansion, Reiss is quoted as saying:
  • "I remember thinking, I've made a terrible mistake and I have to find this mistake"
  • Others said: “[Riess] did a lot after the initial result to show that there was no sneaky effect due to dust absorption“
  • Reiss did make a mistake - Redshift does occur in dust No Universe expansion, accelerated or otherwise
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  • Astronomers Schmidt, Pearlmutter, and Reiss received the 2011 Physics Nobel for discovery of an accelerated expanding Universe

Questions & Papers

  • Email: nanoqed@gmail.com
  • http://www.nanoqed.org
  • 2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
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