15 simulate the motion of two atoms with your hands

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Unformatted text preview: Simulate the motion of two atoms with your hands for case Etot = -0.4ε Simulate it on the computer! (More fun ;) Atoms in Motion (written by UCD student) You can DL this for your computer! 3.2.1 - Particle model of Ebond Geometrical picture of little spheres packing closely. Each touching neighbor pair is one “bond” What if you have 100 atoms? NA atoms? You can’t count all those bonds M. Chertok, Physics 7A 14 Connect: micro to macro Macroscopic total energy: Etotal = Ebond + Ethermal [ = U = Einternal] Microscopic total energy: Etotal = PEtotal + KEtotal What happens at T=0K? T=0K means Ethermal=0 Also, T=0K means no motion, so KEtotal=0 So, at T=0K, Etotal = Ebond = PEtotal PEtotal is related to the well-depth! How? M. Chertok, Physics 7A 15 Particle Model of Ebond Model #5 Nearest neighbors Nearest neighbor pair (n-n) # of nearest neighbors Non-nearest neighbor pairs Total # of n-n pairs Bond energy Ebond = ∑all pairs (PEpair-wise) Ebond ≈ -(total # of n-n pairs) × ε M. Chertok, Physics 7A 16 DLM10 3.2.2 FNTs from DLM09 Bond energy for cluster of 6 atoms Rule of thumb: if you can count the # n-n pairs, then do so Compare Ebond predictions from model to empirical values for molecules 3.2.3 Ebond for systems of many atoms 3.2.4 Particle Model of Thermal Energy M. Chertok, Physics 7A 17 Macroscopic cluster NA is Avagadro’s number NA = 6.02 x 1023 For such a sample, can’t count bonds to “derive” Ebond Instead, need a shortcu...
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