Invalidity of Molecular Dynamics in Heat Transfer Thomas Prevenslik QED Radiations Discovery Bay,...
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Invalidity of Molecular Dynamics in
Heat Transfer
Thomas PrevenslikQED Radiations
Discovery Bay, Hong Kong
2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
1
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?
Introduction
22nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
MD and FE Restrictions
MD and FE are restricted by Statistical Mechanics (SM) to atoms having thermal heat capacity
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
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?
Problem
52nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
Heat Capacity of the Atom
1
kT
hcexp
hc
E
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
2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
Conservation of Energy
Lack of heat capacity by QM precludes EM energy conservation in discrete nanostructures by an increase in
temperature, but how does conservation proceed?
ProposalAbsorbed 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
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
TIR Confinement
82nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
QED Heat Transfer
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).
102nd 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, 201211
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 endCharge 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, 201212
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..
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
RecommendationEstimate the time-history of QED radiation and use in FE simulations to determine the effect on macroscopic surroundings. MD may not even be necessary
Conclusions
132nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 2012
Expanding Unverse
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
15Redshift 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
16
Nobel Mistake Astronomers Schmidt, Pearlmutter, and Reiss received the
2011 Physics Nobel for discovery of an accelerated expanding Universe
Questions & Papers
Email: [email protected]
http://www.nanoqed.org
2nd Inter. Conf. Nanomaterials: Applcations & Properties - NAP, Alushta, Sept. 17-22, 201217