Atom Energy in Crystals: Gibbs Free Energy

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Discussion Overview

The discussion revolves around the energy of atoms at the surface of a crystal compared to those in the bulk, specifically in relation to Gibbs free energy. Participants explore the implications of surface energy and the characteristics of surface atoms versus bulk atoms.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that surface atoms are under-coordinated, leading to a higher average potential energy compared to bulk atoms.
  • One participant notes that surface atoms have a higher electrical potential energy due to the inward electric force acting on them.
  • There is a question about whether surface energy can be considered simply as the excess energy of surface atoms due to unsaturated bonds.
  • A later reply distinguishes between "unrelaxed" surface energy and other forms of surface energy, indicating a complexity in the concept.

Areas of Agreement / Disagreement

Participants express differing views on the nature of surface energy and its relationship to Gibbs free energy, indicating that multiple competing perspectives remain without a clear consensus.

Contextual Notes

The discussion highlights ambiguities in defining energy per atom in solids and the potential dependence on various factors such as coordination and bond saturation. There are unresolved aspects regarding vibrational free energy and stress-volume energy related to surface atoms.

aaaa202
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Does atom at the surface of a crystal have more or less energy than those in the bulk? And how does this relate to their Gibbs free energy?
 
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The notion of energy per atom in a solid is a bit ambiguous.
The surface atoms are under-coordinated (less number of bonds), thus it is expected that the average potential energy on the surface should be higher compared to the bulk.
I do not recall any general conclusion about the vibrational free energy of the surface or its stress-volume energy.
 
At atom at the surface has a higher electrical PE than an atom in the bulk. This is because the electric force on the atom is inward.
 
So is the surface energy simple the excess energy that the surface atoms have due to unsaturated Bonds?
 
aaaa202 said:
So is the surface energy simple the excess energy that the surface atoms have due to unsaturated Bonds?

This is the "unrelaxed" surface energy.
 

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