Classical spin system. Ising model.

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SUMMARY

The discussion centers on the energy function of the Ising model in classical spin systems, specifically the equation ##E=-S_1S_2## with a coupling constant ##J=1##. It clarifies that negative energy values arise from the relative nature of energy scales, akin to gravitational potential energy where reference levels can be adjusted. The participants emphasize that energy can be shifted by a constant, allowing for flexibility in defining energy levels, often setting ##const=0## for simplicity.

PREREQUISITES
  • Understanding of classical spin systems
  • Familiarity with the Ising model
  • Basic knowledge of energy functions and potential energy
  • Concept of reference energy levels in physics
NEXT STEPS
  • Research the implications of negative energy in the Ising model
  • Explore the relationship between spin orientation and energy states
  • Study gravitational potential energy and its reference levels
  • Investigate energy shifts in various physical systems
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Physicists, researchers in statistical mechanics, and students studying classical spin systems and energy functions.

LagrangeEuler
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Energy function ##E=-S_1S_2##. I took ##J=1##. If spin are oriented parallel energy is negative. How could energy be negative?
 
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Energy scales are often relative. The reference level in the spin system is set to zero.

It's similar to how when talking about gravitational potential energy (close to earth) we typically set our reference energy level to ground level, so that energies are positive. However, when talking about gravitational potential energies between planets, etc., we often chose our reference level to be at infinite separations, so that the energy is negative.

However, we can always shift these energies by a constant energy level (equivalent to shifting our reference level).
 
If I understand you well you can always put ##E=const-JS_1S_2##. I just sometimes say ##const=0##.
 

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