What is the explanation for this discrepancy?

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SUMMARY

The discussion centers on the discrepancy observed in the calculated Bulk modulus for metals using the free electron model, which yields a value twice that of experimental results. The contributor questions the absence of contributions from ion cores and bound electrons in the free electron model, suggesting these may have a negative impact on the Bulk modulus. The conversation also touches on the relationship between magnetic susceptibility and the contributions from free electron paramagnetism and diamagnetism, with the latter being attributed to ion cores and bound electrons. This raises the question of how the Bulk modulus can exhibit a negative contribution, despite the model's surprisingly accurate estimate of compressibility.

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JohanL
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When I calculate the Bulk modulus for a metall with the free electron model
I get a value that is twice the experimental value.

I find this strange.
With the free electron model i don't get the contribution from the ion cores and the bound electrons, right?
Do these have a negavite contribution to the bulk modulus.
If so, why?

The magnetic suceptibility has a positive contribution from the free electron paramagnetism and a negative from the diamagnetism. Where the diamagnetism comes from the ion cores and the bound electrons. This i can understand...but how can the bulk modulus have a negative contribution??
 
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I never worried about this difference before. To me, it is surprising that this estimate of the compressibility is so good. After all, in equilibrium the real metal does not exert any outward pressure at all, because the positive ions keep the electrons inside.
 

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