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| An atomic solid is composed of a regular array of atoms interacting through their mutual potential. Each atom behaves as a harmonic oscillator with three degrees of freedom, and the internal energy of the solid is associated with the temperature dependent mean energy of these oscillators. Each oscillator has the same natural frequency and as they are lightly coupled, the total energy is shared between them with the probability of a given oscillator having an energy E being given by the Boltzmann probability: P(E) = exp( -E/kT), where k is Boltzmann's constant (8.6 x 10-5eV/K) and T is the Kelvin temperature of the material. As this probability expression suggests, the energy of a given oscillator is time dependant as it receives and donates energy to the 'thermal bath' represented by all the other oscillators in the material. This behavior is the source of the thermal fluctuations in the lattice | ||||||